Water Heater
In a water heater, the dip tube brings in cold water from your home’s water lines to the inside base of the tank. The heating element turns on until the water heats to your set temperature. As the water heats, it rises to the top of the tank where the hot water supply, always located at the top, will exit your water heater and flow to your faucet or whatever fixture you’re trying to get hot water from.
There four basic types of residential water heaters: tank-type, hybrid, tank-less, and point-of-use. Tank-type heaters are by far the most popular kind but tank-less water heaters are growing exponentially each year. Hybrid models are relatively new, but worth considering if you’re seeking maximum energy efficiency. And point-of-use heaters are ideal for quickly delivering hot water to faucets and appliances located far from the home’s main water heater.
- A gas powered water heater has cold water brought from the home water lines into the tank Through a dip tube, cold water is brought into the tank of a gas-powered water heater from the home’s water lines.
- The water that has arrived to the tank is heated with a “heating element,” which in this case is the gas burner.
- This heating element burns gas and therefore releases remarkably hotand also toxic air up through a chimney in the middle of the water heater tank which is the center, the focus of the circumference of the tank water heater.
- As the chimney moves this toxic air outside, it also heats the metal of the interior of the chimney. During the heating process of this chimney, the water surrounding it is also heated. The exterior is just warm because that heat is not transferred to the exterior thanks to an insulation.
- Warm water rises to the top of the water heater tank and is ready to be moved throughout the home through the heat-out pipe when it is required by a faucet or any corresponding fixture.
- As you open the faucet to request hot water, cool water is brought in through the dip tube, displacing the hot water and pushing it through the heat-out pipe.
- Homeowners can set the temperature they would like their water to be heated at by using a thermostat. The thermostat is connected to the gas line and directs the appropriate amount of gas to the burner to achieve the temperature the homeowner has set.
- There are also a number of safety features on water heaters. When the water temperature or pressure inside the tank are too high, the temperature and pressure-relief valve, or the T and P valve, will open and release water. The purpose of this is to prevent the water heater from exploding.
- Opening the drain valve will enable the homeowner to drain the water heater once a year in order to reduce sediment build up, which is an annual maintenance task.
For tankless water heater owners, the process is slightly different. Because there is no storage tank, there is a heating exchanger that is used to heat the water. It uses gas as the heat source, which allows the heat to transfer from the heat exchanger to the water. Unlike storage water heater tanks, you won’t run out of hot water and it’s a great option for homes that have several family members or for those homes that use a lot of hot water.
The most popular type of water heaters in the US is the conventional storage water heater, where water is heated to a set temperature and then stored at that temperature in a tank until a homeowner turns on the “hot” water tap.
In household and commercial usage, most North American and Southern Asian water heaters are the tank type, also called storage water heaters. These consist of a cylindrical vessel or container that keeps water continuously hot and ready to use. Typical sizes for household use range from 75–400 L (20–100 US gallons). These may use electricity, natural gas, propane, heating oil, solar, or other energy sources. Natural gas heaters are most popular in the US and most European countries, since the gas is often conveniently piped throughout cities and towns and currently is the cheapest to use. In the United States, typical natural gas water heaters for households without unusual needs are 150–190 L (40–50 US gal) with a burner rated at 10.0–11.7 kilowatts (34,000–40,000 BTU/h).
This is a popular arrangement where higher flow rates are required for limited periods. Water is heated in a pressure vessel that can withstand a hydrostatic pressure close to that of the incoming mains supply. A pressure reducing valve is sometimes employed to limit the pressure to a safe level for the vessel. In North America, these vessels are called hot water tanks, and may incorporate an electrical resistance heater, a heat pump, or a gas or oil burner that heats water directly.
A vast majority of homes have conventional tank-type water heaters, which are powered by either gas or electricity. Generally speaking, gas water heaters are more expensive to buy than electric models, but cost less to operate because gas is cheaper than electricity. However, electric water heaters are more efficient than gas models and have higher energy-factor ratings.
As its name implies, a tank-type heater has a large insulated storage tank that holds hot water until it’s needed. Here’s how it works: Cold water enters the bottom of the tank and is heated by either a gas flame below the tank or electric elements suspended inside the tank. An adjustable thermostat regulates and maintains the water temperature. A pressure-relief valve prevents an excessive buildup of pressure inside the tank.
When hot water is called for at a faucet or appliance, heated water is pumped out the top of the tank and through the home’s hot-water supply pipes. As the water level drops in the tank, it’s automatically refilled with cold water, and the whole process starts over again.
Tank-type water heaters come in various sizes, ranging from about 20 to 80 gallons, but a 40- or 50-gallon tank is sufficient for most households. If you’re shopping for a gas water heater, consider a condensing unit. It operates at higher efficiency by capturing hot exhaust gases before they exit the flue and redirecting them through a coil at the base of the unit. The incoming cold water then absorbs much of the heat from the gases.
The downside of tank-type water heaters is that they hold a limited supply of hot water and may struggle to supply enough hot water during high-demand periods. Also, tank-type heaters burn energy (gas or electricity) day and night to maintain the water temperature, regardless of whether or not anyone’s using hot water, a phenomenon known as standby heat loss.
Where hot-water space heating boilers are installed, domestic hot water cylinders are usually heated indirectly by primary water from the boiler, or by an electric immersion heater (often as backup to the boiler). In the UK these vessels are called indirect cylinders and direct cylinders, respectively. Additionally, if these cylinders form part of a sealed system, providing mains-pressure hot water, they are known as unvented cylinders. In the US, when connected to a boiler, they are called indirect-fired water heaters.
Compared to tankless heaters, storage water heaters have the advantage of using energy (gas or electricity) at a relatively slow rate, storing the heat for later use. The disadvantage is that over time, heat escapes through the tank wall and the water cools down, activating the heating system to heat the water back up, so investing in a tank with better insulation improves this standby efficiency. Additionally, when heavy use exhausts the hot water, there is a significant delay before hot water is available again. Larger tanks tend to provide hot water with less temperature fluctuation at moderate flow rates.
Volume storage water heaters in the United States and New Zealand are typically vertical cylindrical tanks, usually standing on the floor or on a platform raised a short distance above the floor. Volume storage water heaters in Spain are typically horizontal. In India, they are mainly vertical. In apartments they can be mounted in the ceiling space over laundry-utility rooms. In Australia, gas and electric outdoor tank heaters have mainly been used (with high temperatures to increase effective capacity), but solar roof tanks are becoming fashionable.
Tiny point-of-use (POU) electric storage water heaters with capacities ranging from 8–32 L (2–6 gallons) are made for installation in kitchen and bath cabinets or on the wall above a sink. They typically use low power heating elements, about 1 kW to 1.5 kW, and can provide hot water long enough for hand washing, or, if plumbed into an existing hot water line, until hot water arrives from a remote high capacity water heater. They may be used when retrofitting a building with hot water plumbing is too costly or impractical. Since they maintain water temperature thermostatically, they can only supply a continuous flow of hot water at extremely low flow rates, unlike high-capacity tankless heaters.
Parts Of A Water Heater
Let’s take a quick look at the components that work together in your water heater to make your morning shower so satisfying:
Tank
The inner shell of a water heater is a heavy metal tank containing a water protective liner that holds 40 to 60 gallons (151 to 227 liters) of hot water at around 50 to 100 pounds per square inch (PSI), within the pressure range of a typical residential water system. The exterior of the tank is covered in an insulating material like polyurethane foam. Over that, there’s a decorative outer shell and possibly an additional insulating blanket.
Most water heaters found in homes throughout the US feature large, insulated tanks which store your hot water. These water heater tanks come in different sizes, typically holding between 20 and 80 gallons. The size of the tank should correspond with the number of people in the home needing hot water, and the average household tank has a 40-60 gallon capacity.
This style of water heater features a tank that holds water to be heated. This means that the capacity of the tank determines how much hot water you have available at once. The tank is insulated so that when the water heats up, it remains warm until it is needed.
Dip tube
The dip tube is where cold water from your home’s municipal supply, well, or another water source, enters the tank. Your main water line splits just before the water heater. When you turn on the cold water tap, the water is piped from the main valve through the cold water service line. The water that comes through the hot water tap passes through the dip tube into the tank. This is before the water travels through the hot water service line. The dip tube is located at the top of the tank. The cold water enters here and is then heats from the bottom of the tank.
This is the tube where water enters into the tank to replenish the hot water being used. It’s located at the top of the tank and goes down to the bottom where the water is then heated.
Water enters the water heater through the dip tube at the top of the tank and travels to the tank bottom where it’s then heated.
Shut-off valve
Outside of the water heater is a shut-off valve. This shuts off the flow of water into the tank.
The shut-off valve stops water flow into the water heater. It’s a separate component from the heater located outside and above the unit.
Heat-out pipe or Hot supply
This is the pipe that brings hot water out of the tank to the hot water service line. It’s located at the top. As hot water has less density than cold water, and heat rises by nature, the hottest water rises to the top of the tank.
This is located inside the tank at the top; this port allows the hot water to exit the tank and flow through your home’s pipes to whatever appliance you want hot water from.
Suspended toward the top of the tank’s interior, the heat-out pipe allows the hot water to exit the water heater.
Thermostat
This is a thermometer- and temperature-control device. Some electric water heaters have a separate thermostat for each element.
This serves as the temperature control device to determine how hot the water will get. You should be able to adjust the thermostat to meet your needs.
The water heater’s thermostat controls the temperature of the water inside the tank. The recommended water temperature setting by most manufacturers is between 120 to 140 degrees Fahrenheit. 120-140 degrees is a great range because it’s hot enough for household use without the risk of scalding. If you have children in your home, you may want to keep it at a lower temperature.
Additionally, setting your water heater to a lower temperature also saves energy and you can even turn down the temperature before you go on vacation to save energy. Look at the bottom of the tank and you’ll find a dial or knob to adjust the temperature. For an electric water heater, you’ll have to pull a protective cover off to access the dial.
While standard tank water heater devices have a thermostat on the exterior surface that enables the homeowner to measure and adjust the temperature of the water, mobile water heaters have to be non-adjustable, as per legal requirements from federal agency HUD. This fact, is one of the main differences between a standard water heater and a mobile water heater, but not the only difference. Therefore I invite you to read our article about it.
Heating element
Electric water heaters have heating elements inside the tank to heat the water. Gas water heaters use a burner and chimney system instead.
Gas water heaters use a flame underneath the tank to heat the water, while electric water heaters use a heating element. Both are located at the bottom of the tank.
Drain valve
The drain valve is located near the bottom, outside of the tank. As its name suggests, the drain valve is used to drain out sediment that builds up inside the tank.
This valve is not a part of your water heater’s daily use, but was created to easily empty the tank to replace the elements and remove sediment or to move the tank to a new location. This is located near the bottom of the tank on the outside.
Located near the bottom of the exterior housing, the drain valve makes it easy to empty the tank to replace the elements, remove sediment or move the tank to another location.
Pressure relief valve
The water inside of the tank is highly pressurized. The pressure relief valve prevents pressure from building up to a dangerous extent.
The pressure release valve opens to lower the pressure when it reaches about 150 psi.
This safety device keeps the pressure inside the water heater within safe limits.
Temperature control valve
The temperature control valve opens to release heat and moderate temperature when the water reaches, for example, over 120 degrees Fahrenheit.
Sacrificial anode rod
This is a rod made of a metal that rusts faster than the metal making up the water heater tank. This anode rod prevents the water heater tank from rusting, as long as it is replaced every 1-2 years after rusting away.
The anode rod is another safety measure. It prevents the tank from rusting through electrolysis. This means that the metal-coated steel rod (generally coated in aluminum, zinc, or magnesium) rusts instead of the steel lining of the tank’s interior.
Made of magnesium or aluminum with a steel core, the sacrificial anode rod is suspended in the water heater tank to help retard corrosion.
This rod is suspended in the water tank to help keep your tank from corroding. This acts similar to a magnet by attracting corrosive minerals in the water to the rod instead of eroding the tank. It’s usually made of magnesium or aluminum with a steel core. This should be replaced about every 1-2 years, depending on how hard your water is.
That is the reason why it is called “sacrificial”. The anode rod “sacrifices” itself so your water tank does not rust and only a cheap anode rod has to be replaced.
Process For Heating The Water
Let me put it in one phrase for you, and then we will go in more detail to explain the process that takes place inside the water heater in one paragraph, below.
The dip tube brings in cold water from your home’s water lines to the inside base of the tank. The heating element turns on until the water heats to your set temperature. As the water heats, it rises to the top of the tank where the hot water supply, always located at the top, will exit your water heater and flow to your faucet or whatever fixture you’re trying to get hot water from.
- A gas powered water heater has cold water brought from the home water lines into the tank Through a dip tube, cold water is brought into the tank of a gas-powered water heater from the home’s water lines.
- The water that has arrived to the tank is heated with a “heating element,” which in this case is the gas burner.
- This heating element burns gas and therefore releases remarkably hotand also toxic air up through a chimney in the middle of the water heater tank which is the center, the focus of the circumference of the tank water heater.
- As the chimney moves this toxic air outside, it also heats the metal of the interior of the chimney. During the heating process of this chimney, the water surrounding it is also heated. The exterior is just warm because that heat is not transferred to the exterior thanks to an insulation.
- Warm water rises to the top of the water heater tank and is ready to be moved throughout the home through the heat-out pipe when it is required by a faucet or any corresponding fixture.
- As you open the faucet to request hot water, cool water is brought in through the dip tube, displacing the hot water and pushing it through the heat-out pipe.
- Homeowners can set the temperature they would like their water to be heated at by using a thermostat. The thermostat is connected to the gas line and directs the appropriate amount of gas to the burner to achieve the temperature the homeowner has set.
- There are also a number of safety features on water heaters. When the water temperature or pressure inside the tank are too high, the temperature and pressure-relief valve, or the T and P valve, will open and release water. The purpose of this is to prevent the water heater from exploding.
- Opening the drain valve will enable the homeowner to drain the water heater once a year in order to reduce sediment build up, which is an annual maintenance task.
For tankless water heater owners, the process is slightly different. Because there is no storage tank, there is a heating exchanger that is used to heat the water. It uses gas as the heat source, which allows the heat to transfer from the heat exchanger to the water. Unlike storage water heater tanks, you won’t run out of hot water and it’s a great option for homes that have several family members or for those homes that use a lot of hot water.
Let’s take a close-up look at what’s going on inside a water heater’s tank to see how simply and elegantly it does its job.
Gas water heaters use a flame underneath the tank to create heat, while electric water heaters use a “heating element” to warm the water.
Each tank has inlets that enters and exits the tank to move the water to where you need it (i.e. shower, dishwasher, etc.). There’s also a thermostat to monitor the temperature and a pressure relief valve to help ensure the heating process doesn’t produce unsafe levels of water pressure.
Gas and electric water heaters are both tank-type water heaters. These are the most common types of water heaters found in homes. They operate largely on the same principle, differing mainly in their respective sources of heat. The following process applies, regardless of the heating mechanism.
Water travels through the main water line into your home. Just before the water heater, the line splits into two separate pathways which make up your home’s water intake system.
You turn on the hot water tap. Cold water that is still not hot passes the shut-off valve, travels through the dip tube and enters the water heater tank.
The heating mechanism at the bottom of the tank heats the water according to the thermostat setting. The water that just entered is displaced to the bottom of the tank, and the hottest water rises to the top.
So, you turned on the hot water tap, and more water entered the tank through the dip tube. Under immense pressure, hot water at the top of the tank is displaced as new cold water enters the tank. This hot water travels up through the heat-out pipe to the hot water tap.
How The Parts Of A Water Heater Are Working Together
A water heater’s thermostat controls the temperature of the water inside the tank. Normally, you can set the temperature anywhere between 120 and 180 degrees Fahrenheit (49 to 82 degrees Celsius). The water temperature setting recommended by most manufacturers is between 120 to 140 degrees Fahrenheit (49 to 60 degrees Celsius). This is hot enough to be efficient for household use, but not so hot that it can pose a scalding risk. If there are children living in your home, it’s wise to stay closer to the lower end of the range.
Setting your water heater to a lower temperature saves energy, too, and if you remember to dial back the heat when you go on vacation, you’ll experience even more energy savings. Usually, the thermostat is located underneath a protective cover plate and has a knob or dial you can turn to set the temperature.
The dip tube feeds cold water from your home’s water lines to the bottom of the tank’s interior, where the water starts to warm up. The heating mechanism, either a burner or an element, stays on until the water reaches temperature. As the water heats, it rises to the top of the tank. The heat-out pipe is located near the top of the tank. Water exiting the water heater at the top is always the hottest in the tank at any given moment because it’s the nature of hot water to rise above denser, cold water.
The secret to a water heater’s design for separating cold, incoming water from hot, outgoing water is that it relies on the principle that heat rises to do the hard part. The position of the heat-out pipe at the top of the tank does the rest.
The Recovery Time In The Tank Water Heater
It’s important to mention a hot water heater’s recovery time. For every gallon you draw out, you’re putting cold water back into the tank that needs to get re-heated. So if all the water in your tank starts at 120 degrees, but you’re adding 50-degree water into the mix, the temperature will slowly go down as you’re consuming hot water. Unfortunately, with tank-style water heaters, they will never heat the water as fast as you can use it. The thermometer uses a differential where you’re heater won’t fire up as soon as the temperature drops below your set point, otherwise it would constantly be turning on. This helps conserve energy.
You can do things like install a low-flow showerhead or a recirculating pump, which reduce the amount of water you use and helps extend the amount of time you have hot water. Plus, it helps you save money on your gas bills.
Tank Water Heater Maintenance
This is the maintenance plan for a water heater that I will recommend to you.
- Set the thermostat on the water heater on a safe temperature. Most manufacturers recommend around 120 degrees to save money on heating bills.
- Flush out sediment from your tank annually. Otherwise, a water heater can stop working prematurely.
- Check and change the anode rod. This rod keeps your tank from rusting, by “sacrificing” itself and rusting.
- Test your pressure relief valve by cooling the water, putting a bucket under the pipe, and opening the valve.
Because the tank works to store water constantly, you will need to clean it out regularly to increase the lifespan of your water heater. You should clean your water heater tank up to twice a year to remove sediment and mineral scale and help reduce corrosion. This is not necessary and your water heater will usually work without being cleaned, but it may not last as long. The typical lifespan of a conventional storage tank water heater is around twelve years.
Water Heater Buying Guide: User Requirements To Consider
1. Warranty:
Water heater warranties can vary greatly both in cost and length. Because your water heater is such an integral part of your family’s day to day life, you should always pay close attention to the warranty terms when choosing a new water heater. In the event that it is damaged, you may be able to get a new one without shelling out thousands of dollars on demand. Warranty ranges are typically around 2–10 years, but you can find manufacturers who offer up to a 12-year warranty. If you own your home, you might consider a longer warranty, even if you must pay a bit extra, to avoid any surprise costs in the future. Because water heaters can break, and they are so important, we suggest you choose the longest warranty available.
2. Drain Valves: Plastic or Brass?
The drain valve is located near the bottom of your water heater and is used to drain the water heater before maintenance or to make it easier to lift while moving it. This valve is typically either made of brass or plastic. In the event that you need to replace your water heater drain valve, or you are purchasing a new water heater, you will need to decide which type to use. Both plastic and brass are particularly cost-efficient options. Plastic may be less reactive, although neither material is corrosive. Brass is much more durable than plastic, and also more malleable, so it will take more damage. Brass is not affected by temperature change like plastic may be. This is not a huge decision, but it is still one you will need to make.
3. Anti-Scale Devices:
Mineral scale can cause damage to your water heater and other water-consuming appliances. Certain manufacturers include anti-scale devices in their water heater. This device moves the water at the bottom of the tank. The constantly moving water is less prone to mineral build-up, which can increase the lifespan of your water heater. This feature may work, but there are other factors besides mineral build up that can damage your water heater. It is not necessary to purchase a water heater with an anti-scale device and, with a lengthy warranty, you probably don’t need one.
4. Glass-Lined Tanks:
You may notice that some water heaters include a glass lining inside them. This lining is actually porcelain enamel and the coating helps to protect the water heater (which is usually made from steel) from corrosion. The enamel coating can do wonders in extending the life of your water heater but, due to the coating process, areas of steel are most often still left exposed. The ceramic enamel coating is becoming more and more popular and may even be a standard design for some manufacturers today. Again, this is not a necessary inclusion, but it could definitely slow down the corrosion process inside your water heater tank.
5. Digital Displays:
Water heaters with digital displays are convenient because you can easily adjust your water heater settings to fit your personal needs. You can easily adjust the output of your water heater, the water temperature, and some models even have a scheduling feature, which allows you to input the hours your house is occupied in order to increase the energy efficiency of the water heater by shutting off when you’re away. Water heaters without the digital display will often only show basic readings, like overall temperature and water pressure. The digital display is definitely a modern water heater feature you want.
6. Capacity:
Determining the capacity of your water heater tank depends solely on the number of people using water in your house. It can be difficult to determine how large of a tank you will need since each person’s water usage may vary greatly. You can use the first-hour rating (FHR) to help determine the water heater size your family needs. To calculate your family’s FHR, count the number of people in your home and multiply by twelve. This means that a family of four has an FHR of 48 gallons. You can check the FHR of your water heater to determine if it will heat enough water for your home. Here is another good rule of thumb:
If your home only has one or two people, a 30-gallon tank should be sufficient.
- If your home has two or three people, you may need a 40-gallon water heater tank.
- If your home has three to four people, you should opt for something larger, around 40–50 gallons.
- For more than five people, you should consider a tank that holds 55 gallons or more.
- For eight people or more, you may need two water heaters to supply enough hot water to your home.
Of course, for tankless water heaters, you will need to use your FHR to determine what size to buy.
Reasons To Replace An Existing Water Heater
1. Your Warranty is Out
One good way to know that it may be time for an upgrade is when you’ve surpassed your 12-year warranty by a few years. Not only do you no longer have coverage for fixing your water heater if any sudden damages occur, but chances are your water heater’s design is pretty outdated and is using way more energy than necessary. This could be costing you tons of excess money every month without you noticing. If your water heater has lived long past its life expectancy, it may be time to toss it out and replace it with an upgrade.
2. Your Water Heater is Leaking
Usually, when your water heater is leaking, you’ll need a plumber to fix the issue. This can be really costly and time-consuming. Sometimes, water heater leaks can be hard to find, and a lot of water damage can occur before the issue is fixed. If you have a leak, you can have a plumber look at it. If it’s bad enough, you’ll probably be better off buying a new water heater instead of paying to fix the leak.
3. You Run Out of Hot Water When You Need It
If you find that you are frequently taking lukewarm showers or running out of hot water while doing the dishes, you may not have a water heater big enough to surmount the hot water volume your family uses. This means you may need an upgrade to a water heater with a bigger tank.
4. Your Building Codes Changed
Another reason you may need a new water heater is if it no longer fits your community’s building codes. You should check your local building codes regularly and, if you’ve moved states, you may have different building codes than before. If your building codes have changed, your water heater may need to as well.
Tankless Water Heater
A tankless water heater, as you can probably guess, has no tank. Instead, there are super-heated coils that fill with water and heat water in a flash as you need it, which is why it is alternatively known as an on-demand water heater. This is great for heating water quickly, even for large families who need a large amount of hot water at once. This style of water heater comes in different sizes, and you do need to ensure that you have the right size for your household, as a smaller tankless water heater will not be able to keep up with your water usage otherwise and it will result in lukewarm or cold water. These models work well in homes that use natural gas to power their water heater, but larger models require a larger gas line and more gas to run correctly. Larger tankless hot water heaters that run on electricity may require you to increase the electricity capacity of your home, which could be costly.
These high-power water heaters instantly heat water as it flows through the device, and do not retain any water internally except for what is in the heat exchanger coil.
Tankless water heaters are incredibly energy efficient because they only heat water on demand instead of holding heated water all day, even when it is not being used. Assuming you get a model large enough for your household, you will have unlimited hot water all the time.
Instead of storing hot water in a perpetually-heated tank, tankless water heaters only heat water when it’s needed.
When you turn on a hot water tap, a flow sensor in the tankless water heater unit activates. If the tankless unit is gas-powered, this sensor turns on a fan inside of the unit, drawing in air, opens the gas valve, and ignites the burner.
With an electric tankless unit, the sensor activates an electric heating unit. In either case, the heat exchanger inside the unit is warmed, which heats the water to a preset temperature. The water passes through the unit to the tap. This bypasses the process of storing a tank full of hot water and the energy needed to maintain a high temperature on a constant basis.
Tankless water heaters save energy, reduce the risk of leaks, and are not constrained by a finite supply when hot water is in high demand. You can’t run out of hot water with a tankless unit, as there is no tank to be depleted. Tankless water heaters are also safer and longer-lasting. However, these advantages come with a higher price tag upfront than with a conventional hot water heater.
Although tank style water heaters are still very popular, especially in the U.S., tankless water heaters are gaining in popularity. Where a tank-style water heater continuously heats the water to make it available when you need it, a tankless system creates hot water on demand. Although this can mean big energy savings, a tankless system can initially cost up to three times as much as a standard water heater setup.
Tank-less water heaters are compact, wall-hung units that provide hot water for the entire house—not just single faucet—and are often called instantaneous or on-demand water heaters. And as you may have guessed, this type of water heater has no bulky storage tank.
Here’s how it works: A tank-less water heater sits idle until a hot-water tap is opened in the house. Then, cold water is drawn into the unit and a flow sensor activates an electric heating element or gas-fired burner, which warms an internal heat exchanger. As the cold water passes over the heat exchanger it’s warmed to the preset temperature. Hot water then exits the heater and travels directly to the faucet or appliance—not to a storage tank. Combustion gases, produced by gas-fired units, are exhausted through a dedicated, sealed vent pipe.
When the hot-water tap is turned off, the heater shuts down, and therein lies the main benefit of tank-less water heaters: Since there’s no storage tank to keep filled, tank-less models only heat water when it’s called for. As a result, a tank-less water heater delivering 40 gallons of hot water per day uses about 34% less energy than a standard water heater.
And for even greater energy efficiency, consider a condensing tank-less water heater, which operate with an efficiency rating between 90% and 98%; non-condensing tank-less units operate at a still-impressive 80% or so.
And because there’s no storage tank, tank-less water heaters provide an unlimited supply of hot water, which is a real bonus for large families. And tank-less heaters last up to 20 years, nearly twice as long as standard tank-type water heaters. On the downside, tank-less water heaters do cost more to purchase and install than standard water heaters, and they’re often more costly to repair.
The market is moving more towards tankless water heaters due to their small size, energy savings, and long lifespan. While regular water heaters have a lifespan of about ten years, tankless versions can last more than 20.
Copper heat exchangers are preferred in these units because of their high thermal conductivity and ease of fabrication.
Tankless heaters may be installed throughout a household at more than one point-of-use (POU), far from a central water heater, or larger centralized models may still be used to provide all the hot water requirements for an entire house. The main advantages of tankless water heaters are a plentiful continuous flow of hot water (as compared to a limited flow of continuously heated hot water from conventional tank water heaters), and potential energy savings under some conditions. The main disadvantage is their much higher initial costs.
In a comparison to a less efficient natural gas fired hot water tank, on-demand natural gas will cost 30% more over its useful life.
A common arrangement where hot-water space heating is employed is for a boiler also to heat potable water, providing a continuous supply of hot water without extra equipment. Appliances that can supply both space-heating and domestic hot water are called combination (or combi) boilers. Though on-demand heaters provide a continuous supply of domestic hot water, the rate at which they can produce it is limited by the thermodynamics of heating water from the available fuel supplies.
Cons Of Tankles Water Heater Devices
The initial investment in purchasing a tankless hot water heater is significantly higher than that of the more traditional style, and it may require larger gas lines or more power capacity than your home currently has (not always), which can be an expensive renovation.
Tankless Water Heater Maintenance
Although there is no tank, you should still clean your tankless water heater at least once a year to remove mineral scale and avoid corrosion. Cleaning may be more difficult as the parts are smaller and more difficult to access.
The lifespan of this style of water heater is more than ten years
Electric Shower Heads
An electric shower head has an electric heating element which heats water as it passes through. These self-heating shower heads are specialized point-of-use (POU) tankless water heaters, and are widely used in some countries.
Electric showers have a simple electric system, working like a coffee maker, but with a larger water flow. A flow switch turns on the device when water flows through it. Once the water is stopped, the device turns off automatically. An ordinary electric shower often but not always has three heat settings: high (5.5 kW), low (2.5 kW), or cold (0 W) to use when a central heater system is available or in hot seasons. Higher power (up to 7.5 KW) and lower power (up to 3.2 KW) versions are also made, as well as versions with 4 heat settings or a variable heat setting.
Heating Process In An Electric Water Heater
An electric water heater works essentially the same way as a gas water heater. It brings cold water in through the dip tube and heats it using the electric “heating element“ inside of the tank. The hot water rises in the tank and is moved throughout the home through the heat-out pipe .
As with the gas water heater, an electric water heater has a thermostat, temperature and pressure relief valve, a drain valve, the tank is insulated, and it has an anode rod.
Energy Utilization Of Electric Showers
The power consumption of electric showers in the maximum heating setting is about 5.5 kW for 120 V and 7.5 kW for 220 V. The lower costs with electric showers compared to the higher costs with tank boilers is due to the time of use: an electric shower uses energy only while the water flows, while a tank boiler works many times a day to keep a quantity of standing water hot for use throughout the day and night. Moreover, the transfer of electric energy to the water in an electric shower head is very efficient, approaching 100%. Electric showers may save energy compared to electric tank heaters, which lose some standby heat
Safety Issues With The Electric Shower Heads
There is a wide range of electric shower heads, with various designs and types of heating controls. The heating element of an electric shower is immersed in the water stream, using an often replaceable nichrome resistive heating element which is often not sheathed and electrically isolated, in which case isolation is provided by earthing electrodes that directly touch the water before it exits the head.
Due to electrical safety standards as well as cost, modern electric showers are made of plastic instead of using metallic casings like in the past. As an electrical appliance that uses more electric current than a clothes washer or a hair dryer, an electric shower installation requires careful planning, and generally is intended to be wired directly from the electrical distribution box with a dedicated circuit breaker and ground system. A poorly installed system with old aluminum wires, bad connections or an unconnected earth wire (which is often the case) may be dangerous, as the wires can overheat or electric current may leak via the water stream through the body of the user to earth.
Difference Between A Tank Gas Water heater And An Electric Water Heater
The difference between a tank water heater and an electric water heater is that in an electric water heater, the water that entered through the dip tube to fill the tank is heated through an electric resistance that heats the water through joule heating process as it is plugged to the power supply, while in a gas tan the heating element is a gas burner.
Heat Pump Water Heater (Hybrid Water Heater)
This water heater hybrid can help save money on electricity because it doesn’t directly generate heat.
This style of water heater is unique in that is uses heat in the air and in the ground to heat water. This means that electricity is only used to move heat from the ground or air to the water, instead of the alternative where electricity is used to generate heat. Heat pump water heaters can use up to 60 percent less electricity than traditional styles of water heaters. Because the pump is on the top, you may need quite a bit of room for this water heater, sometimes up to eight feet of vertical clearance.
A hybrid water heater is a tank-type heater that’s equipped with an electric heat pump. The pump is mounted on top of the water-storage tank and it uses a compact compressor and evaporator coil to capture heat from the room air and then transfer it to the incoming cold water. As a result, a hybrid model uses 60% less energy than a conventional water heater.
Now, you do have to pay a premium for such high efficiency: A hybrid water heater costs nearly twice as much as a standard water heater, but most families recoup that added expense within three to four years through lower electric bills. And state and local energy rebates can shorten the recoup time even more.
Pros And Cons Of Heat Pump Water Heater Devices
The benefit is that this water heater is incredibly energy efficient and, therefore, can be incredibly cost-efficient in the long run.
Because this water heater style relies on pulling heat from the ground or air around it, it will not work very well in cold spaces like basements or in climates where it is excessively cold for long periods throughout the year. It is, however, one of the most expensive styles of water heaters to purchase.
Maintenace required
This water heater has a tank and, like conventional storage tank water heaters, it needs to be cleaned regularly (up to twice per year) to prolong its lifespan.
Solar Water Heaters
A solar powered water heater allows you to draw energy from the sun. This is a great idea if you already have solar panels or are considering adding them.
This style of water heater may be the most energy-efficient of them all and relies on roof-mounted solar panels as its energy source. The energy is transferred to a closed loop system containing a heat-conductive material, which then heats the water in the tank. This can save lots of money on sunny days and works particularly well for those who live in warm, sunny climates. However, this system often requires a backup plan, such as natural gas or electricity, so that the water heater can continue to run on cloudy days.
Increasingly, solar powered water heaters are being used. Their solar collectors are installed outside dwellings, typically on the roof or walls or nearby, and the potable hot water storage tank is typically a pre-existing or new conventional water heater, or a water heater specifically designed for solar thermal.
The most basic solar thermal models are the direct-gain type, in which the potable water is directly sent into the collector. Many such systems are said to use integrated collector storage (ICS), as direct-gain systems typically have storage integrated within the collector. Heating water directly is inherently more efficient than heating it indirectly via heat exchangers, but such systems offer very limited freeze protection (if any), can easily heat water to temperatures unsafe for domestic use, and ICS systems suffer from severe heat loss on cold nights and cold, cloudy days.
By contrast, indirect or closed-loop systems do not allow potable water through the panels, but rather pump a heat transfer fluid (either water or a water/antifreeze mix) through the panels. After collecting heat in the panels, the heat transfer fluid flows through a heat exchanger, transferring its heat to the potable hot water. When the panels are cooler than the storage tank or when the storage tank has already reached its maximum temperature, the controller in closed-loop systems stops the circulation pumps. In a drainback system, the water drains into a storage tank contained in conditioned or semi-conditioned space, protected from freezing temperatures. With antifreeze systems, however, the pump must be run if the panel temperature gets too hot (to prevent degradation of the antifreeze) or too cold (to prevent the water/antifreeze mixture from freezing.)
Flat panel collectors are typically used in closed-loop systems. Flat panels, which often resemble skylights, are the most durable type of collector, and they also have the best performance for systems designed for temperatures within 56 °C (100 °F) of ambient temperature. Flat panels are regularly used in both pure water and antifreeze systems.
Another type of solar collector is the evacuated tube collector, which are intended for cold climates that do not experience severe hail and/or applications where high temperatures are needed (i.e., over 94 °C [201 °F]). Placed in a rack, evacuated tube collectors form a row of glass tubes, each containing absorption fins attached to a central heat-conducting rod (copper or condensation-driven). The evacuated description refers to the vacuum created in the glass tubes during the manufacturing process, which results in very low heat loss and lets evacuated tube systems achieve extreme temperatures, far in excess of water’s boiling
Pros And Cons Of Solar Water Heater Devices
These water heaters are super energy efficient and therefore are very environmentally friendly as well. You can save tons of money every month on electricity if you allow the sun to do most of the powering for your water heater.
These solar powered water heaters are incredibly expensive and sometimes it can take up to 40 years to see a return on your investment. In not favorable weather conditions where there is little to no sun, you may need an alternate source of power for your water heater, which can be a hassle.
Maintenance Required For Solar Water Heater Devices
Again, this system has a tank, which should be cleaned regularly to remove scale and prevent corrosion. You should also consider the necessity of maintenance on the solar panels.
Point Of Use Water Heater
Unlike the previously mentioned whole-house water heaters, point-of-use water heaters are compact, tank-less models that deliver hot water almost instantaneously to one specific location, such as a bathroom sink or shower.
This type of electric heater is most often installed at fixtures located far from the main water heater. Its biggest selling point is that it eliminates the all-to-common annoyance of opening the tap and then waiting for hot water. Such an inconvenience wastes not only time, but an immense amount of water and energy, too.
Most point-of-use units measure only about 10 in. x 13 in., so they easily fit inside of vanity cabinets and closets, and feature simple plug-in installation. Point-of-use water heaters are extremely reliable and can easily last up to 25 years. And since there’s no standby heat loss with point-of-use water heaters, all the energy consumed is delivered at the tap. Of course if there’s not a GFCI electrical outlet nearby to plug in the unit, you’ll have to hire an electrician to install one.
Point Of Use Hot Water Vs Centralized Hot Water
A locational design decision may be made between point-of-use and centralized water heaters. Centralized water heaters are more traditional, and are still a good choice for small buildings. For larger buildings with intermittent or occasional hot water use, multiple POU water heaters may be a better choice, since they can reduce long waits for hot water to arrive from a remote heater. The decision where to locate the water heater(s) is only partially independent of the decision of a tanked vs. tankless water heater, or the choice of energy source for the heat.
Water Heater Thermodynamics And Legal Requirements
Water typically enters residences in the US at about 10 °C (50 °F), depending on latitude and season. Hot water temperatures of 50 °C (122 °F) are usual for dish-washing, laundry and showering, which requires that the heater raise the water temperature about 40 °C (72 °F) if the hot water is mixed with cold water at the point of use. The Uniform Plumbing Code reference shower flow rate is 9.5 l (2.5 US gal) per minute. Sink and dishwasher usages range from 4–11 l (1–3 US gal) per minute.
Natural gas is often measured by volume or heat content. Common units of measurement by volume are cubic metre or cubic feet at standard conditions or by heat content in kilowatt hours, British thermal units (BTU) or therm, which is equal to 100,000 BTU. A BTU is the energy required to raise one pound of water by one degree Fahrenheit. A US gallon of water weighs 8.3 pounds (3.8 kg). To raise 230 l (60 US gal) of water from 10 °C (50 °F) to 50 °C (122 °F) at 90% efficiency requires 60 × 8.3 × (122 − 50) × 1.11 = 39,840 BTU. A 46 kW (157,000 BTU/h) heater, as might exist in a tankless heater, would take about 15 minutes to do this. At $1 per therm, the cost of the gas would be about 40 cents. In comparison, a typical 230 l (60 US gal) tank electric water heater has a 4.5 kW (15,000 BTU/h) heating element, which at 100% efficient results in a heating time of about 2.34 hours. At $0.16/kWh the electricity would cost $1.68.
Energy efficiencies of water heaters in residential use can vary greatly, particularly depending on manufacturer and model. However, electric heaters tend to be slightly more efficient (not counting power station losses) with recovery efficiency (how efficiently energy transfers to the water) reaching about 98%. Gas-fired heaters have maximum recovery efficiencies of only about 82–94% (the remaining heat is lost with the flue gasses). Overall energy factors can be as low as 80% for electric and 50% for gas systems. Natural gas and propane tank water heaters with energy factors of 62% or greater, as well as electric tank water heaters with energy factors of 93% or greater, are considered high-efficiency units. Energy Star-qualified natural gas and propane tank water heaters (as of September 2010) have energy factors of 67% or higher, which is usually achieved using an intermittent pilot together with an automatic flue damper, baffle blowers, or power venting. Direct electric resistance tank water heaters are not included in the Energy Star program, however, the Energy Star program does include electric heat pump units with energy factors of 200% or higher. Tankless gas water heaters (as of 2015) must have an energy factor of 90% or higher for Energy Star qualification. Since electricity production in thermal plants has efficiency levels ranging from only 15% to slightly over 55% (combined cycle gas turbine), with around 40% typical for thermal power stations, direct resistance electric water heating may be the least energy efficient option. However, use of a heat pump can make electric water heaters much more energy efficient and lead to a decrease in carbon dioxide emissions, even more so if a low carbon source of electricity is used. Using district heating utilizing waste heat from electricity generation and other industries to heat residences and hot water gives an increased overall efficiency, removing the need for burning fossil fuel or using high energy value electricity to produce heat in the individual home.
Unfortunately, it takes a great deal of energy to heat water, as one may experience when waiting to boil a gallon of water on a stove. For this reason, tankless on-demand water heaters require a powerful energy source. A standard 120-V, 15-ampere rated wall electric outlet, by comparison, only sources enough power to warm a disappointingly small amount of water: about 0.17 US gal (0.64 l) per minute at 40 °C (72 °F) temperature elevation.
The energy used by an electric water heater can be reduced by as much as 18% through optimal schedule and temperature control that is based on knowledge of the usage pattern.
US minimum requirements
On April 16, 2015, as part of the National Appliance Energy Conservation Act (NAECA), new minimum standards for efficiency of residential water heaters set by the United States Department of Energy went into effect.
All new gas storage tank water heaters with capacities smaller than 55 US gal (210 l; 46 imp gal) sold in the United States in 2015 or later shall have an energy factor of at least 60% (for 50-US-gallon units, higher for smaller units), increased from the pre-2015 minimum standard of 58% energy factor for 50-US-gallon gas units. Electric storage tank water heaters with capacities less than 55 US gallons sold in the United States shall have an energy factor of at least 95%, increased from the pre-2015 minimum standard of 90% for 50-US-gallon electric units.
Under the 2015 standard, for the first time, storage water heaters with capacities of 55 US gallons or larger now face stricter efficiency requirements than those of 50 US gallons or less. Under the pre-2015 standard, a 75 US gal (280 l; 62 imp gal) gas storage water heater with a nominal input of 22 kW (75,000 BTU/h) or less was able to have an energy factor as low as 53%, while under the 2015 standard, the minimum energy factor for a 75-US-gallon gas storage tank water heater is now 74%, which can only be achieved by using condensing technology. Storage water heaters with a nominal input of 22 kW (75,000 BTU/h) or greater are not currently affected by these requirements, since energy factor is not defined for such units. An 80 US gal (300 l; 67 imp gal) electric storage tank water heater was able to have a minimum energy factor of 86% under the pre-2015 standard, while under the 2015 standard, the minimum energy factor for an 80-gallon electric storage tank water heater is now 197%, which is only possible with heat pump technology. This rating measures efficiency at the point of use. Depending on how electricity is generated, overall efficiency may be much lower. For example, in a traditional coal plant, only about 30–35% of the energy in the coal ends up as electricity on the other end of the generator.
Losses on the electrical grid (including line losses and voltage transformation losses) reduce electrical efficiency further. According to data from the Energy Information Administration, transmission and distribution losses in 2005 consumed 6.1% of net generation.
In contrast, 90% of natural gas’ energy value is delivered to the consumer. In neither case is the energy expended exploring, developing and extracting coal or natural gas resources included in the quoted efficiency numbers. Gas tankless water heaters shall have an energy factor of 82% or greater under the 2015 standards, which corresponds to the pre-2015 Energy Star standard.
Water Heater Safety
Explosion Hazards
Water heaters potentially can explode and cause significant damage, injury, or death if certain safety devices are not installed. A safety device called a temperature and pressure relief (T&P or TPR) valve, is normally fitted on the top of the water heater to dump water if the temperature or pressure becomes too high. Most plumbing codes require that a discharge pipe be connected to the valve to direct the flow of discharged hot water to a drain, typically a nearby floor drain, or outside the living space. Some building codes allow the discharge pipe to terminate in the garage.
If a gas or propane fired water heater is installed in a garage or basement, many plumbing codes require that it be elevated at least 18 in (46 cm) above the floor to reduce the potential for fire or explosion due to spillage or leakage of combustible liquids in the garage. Furthermore, certain local codes mandate that tank-type heaters in new and retrofit installations must be secured to an adjacent wall by a strap or anchor to prevent tipping over and breaking the water and gas pipes in the event of an earthquake.
For older houses where the water heater is part of the space heating boiler, and plumbing codes allow, some plumbers install an automatic gas shutoff (such as the “Watts 210”) in addition to a TPR valve. When the device senses that the temperature reaches 99 °C (210 °F), it shuts off the gas supply and prevents further heating.
In addition, an expansion tank or exterior pressure relief valve must be installed to prevent pressure buildup in the plumbing from rupturing pipes, valves, or the water heater.
Scalding
Scalding is a serious concern with any water heater. Human skin burns quickly at high temperature, in less than 5 seconds at 60 °C (140 °F), but much slower at 53 °C (127 °F) — it takes a full minute for a second degree burn. Older people and children often receive serious scalds due to disabilities or slow reaction times.
In the United States and elsewhere it is common practice to put a tempering valve on the outlet of the water heater. The result of mixing hot and cold water via a tempering valve is referred to as “tempered water”.
A tempering valve mixes enough cold water with the hot water from the heater to keep the outgoing water temperature fixed at a more moderate temperature, often set to 50 °C (122 °F). Without a tempering valve, reduction of the water heater’s setpoint temperature is the most direct way to reduce scalding. However, for sanitation, hot water is needed at a temperature that can cause scalding. This may be accomplished by using a supplemental heater in an appliance that requires hotter water. Most residential dishwashing machines, for example, include an internal electric heating element for increasing the water temperature above that provided by a domestic water heater.
Risk Of Incubation Of Bacteria Colonies
Two conflicting safety issues affect water heater temperature—the risk of scalding from excessively hot water greater than 55 °C (131 °F), and the risk of incubating bacteria colonies, particularly Legionella, in water that is not hot enough to kill them. Both risks are potentially life-threatening and are balanced by setting the water heater’s thermostat to 55 °C (131 °F). The European Guidelines for Control and Prevention of Travel Associated Legionnaires’ Disease recommend that hot water should be stored at 60 °C (140 °F) and distributed so that a temperature of at least 50 °C (122 °F) and preferably 55 °C (131 °F) is achieved within one minute at points of use.
If there is a dishwasher without a booster heater, it may require a water temperature within a range of 57–60 °C (135–140 °F) for optimum cleaning, but tempering valves set to no more than 55 °C (131 °F) can be applied to faucets to avoid scalding. Tank temperatures above 60 °C (140 °F) may produce limescale deposits, which could later harbor bacteria, in the water tank. Higher temperatures may also increase etching of glassware in the dishwasher.
Tank thermostats are not a reliable guide to the internal temperature of the tank. Gas-fired water tanks may have no temperature calibration shown. An electric thermostat shows the temperature at the elevation of the thermostat, but water lower in the tank can be considerably cooler. An outlet thermometer is a better indication of water temperature.
In the renewable energy industry (solar and heat pumps, in particular) the conflict between daily thermal Legionella control and high temperatures, which may drop system performance, is subject to heated debate. In a paper seeking a green exemption from normal Legionellosis safety standards, Europe’s top CEN solar thermal technical committee TC 312 asserts that a 50% fall in performance would occur if solar water heating systems were heated to the base daily. However some solar simulator analysis work using Polysun 5 suggests that an 11% energy penalty is a more likely figure. Whatever the context, both energy efficiency and scalding safety requirements push in the direction of considerably lower water temperatures than the legionella pasteurization temperature of around 60 °C (140 °F)
Legionella pneumophila has been detected at the point of use downstream from horizontally-mounted electric water heaters with volumes of 150 Liters.
However, legionella can be safely and easily controlled with good design and engineering protocols. For instance raising the temperature of water heaters once a day or even once every few days to 55 °C (131 °F) at the coldest part of the water heater for 30 minutes effectively controls legionella. In all cases and in particular energy efficient applications, Legionnaires’ disease is more often than not the result of engineering design issues that do not take into consideration the impact of stratification or low flow.
It is also possible to control Legionella risks by chemical treatment of the water. This technique allows lower water temperatures to be maintained in the pipework without the associated Legionella risk. The benefit of lower pipe temperatures is that the heat loss rate is reduced and thus the energy consumption is reduced.
Improvements In Water Heater Technology
Other improvements to water heaters include check valve devices at their inlet and outlet, cycle timers, electronic ignition in the case of fuel-using models, sealed air intake systems in the case of fuel-using models, and pipe insulation. The sealed air-intake system types are sometimes called “band-joist” intake units. “High-efficiency” condensing units can convert up to 98% of the energy in the fuel to heating the water. The exhaust gases of combustion are cooled and are mechanically ventilated either through the roof or through an exterior wall. At high combustion efficiencies a drain must be supplied to handle the water condensed out of the combustion products, which are primarily carbon dioxide and water vapor.
In traditional plumbing in the UK, the space-heating boiler is set up to heat a separate hot water cylinder or water heater for potable hot water. Such water heaters are often fitted with an auxiliary electrical immersion heater for use if the boiler is out of action for a time. Heat from the space-heating boiler is transferred to the water heater vessel/container by means of a heat exchanger, and the boiler operates at a higher temperature than the potable hot water supply. Most potable water heaters in North America are completely separate from the space heating units, due to the popularity of HVAC/forced air systems in North America.
Residential combustion water heaters manufactured since 2003 in the United States have been redesigned to resist ignition of flammable vapors and incorporate a thermal cutoff switch, per ANSI Z21.10.1. The first feature attempts to prevent vapors from flammable liquids and gases in the vicinity of the heater from being ignited and thus causing a house fire or explosion. The second feature prevents tank overheating due to unusual combustion conditions. These safety requirements were made in response to homeowners storing, or spilling, gasoline or other flammable liquids near their water heaters and causing fires. Since most of the new designs incorporate some type of flame arrestor screen, they require monitoring to make sure they do not become clogged with lint or dust, reducing the availability of air for combustion. If the flame arrestor becomes clogged, the thermal cutoff may act to shut down the heater.
A wetback stove or back boiler, is a simple household secondary water heater using incidental heat. It typically consists of a hot water pipe running behind a fireplace or stove (rather than hot water storage), and has no facility to limit the heating. Modern wetbacks may run the pipe in a more sophisticated design to assist heat-exchange. These designs are being forced out by government efficiency regulations that do not count the energy used to heat water as ‘efficiently’ used.
