Is A 20 Gallon Hot Water Heater Big Enough?

Is A 20 Gallon Hot Water Heater Big Enough?

Is A 20 Gallon Hot Water Heater Big Enough?

20-gallon water heaters are a unique size. They’re large enough for smaller homes that don’t require large amounts of hot water, yet they’re an excellent choice for high-demand point-of-use (POU) applications such as bathrooms with showers. 

20 Gallon Water Heater Reviews

When purchasing any water heater there’s a number of things to consider, but smaller heaters, like the 20-gallon size, are unique because of their lower capacity. Although, many of the considerations are the same, they often carry more “weight” because they may have a larger impact on the heaters performance. Here are a few of the critical things to consider:

Size and Weight

Whether you plan to use your 20-gallon water heater as a point-of-use heater or your primary water heating system, you’ll want to consider the water heater’s dimensions. If you’ll have it installed under a cabinet, in a closet, or another tight location, it’s critical to check that the water heater fits. In addition, you’ll want to take into account the added space needed for the electrical and water hook-ups.

If you’ll be installing your water heater on the ground or inside a cabinet, it’s weight won’t really matter. However, if you position it on a shelf or other platform, you’ll want to ensure that the structure will be able to support the weight of the water heater as well as the heated water. This can be easily calculated by adding the heater’s weight to the weight of water. Use this handy calculator to determine how much the heated water weighs.

Location of Water Hook-ups

Water heaters have two water hook-ups. The first is a water inlet, which allows fresh water to enter the tank, and the second is a water outlet, which is where the hot water leaves the tank.

20-gallon water heaters either have these hook-ups located on the top of the tank or the side of the tank. Although there are a few manufacturers, like the American Standard CE-20-AS that has the water hook-ups on both the top and side. This is particularly handy because you can choose which works best for your unique installation.

If you’ll be installing your water heater in a tight space such as inside a cabinet, it’s likely you’ll need a heater with the hook-ups on the side of the tank because there will be a limited amount of overhead space available. 

First Hour Rating

The First Hour Rating (FHR) tells you how many gallons of hot water the unit can provide when it starts with a full tank of hot water. As an example, the Stiebel Eltron 20 Plus has a FHR of 30. This means that you can expect to get 30 gallons of hot water during the first hour of use.

In many cases the FHR may not be a factor worth considering, but if you plan on using your 20-gallon water heater to service a shower, it’s definitely worth your attention.

Tank Lining

A water heater’s biggest enemy is corrosion. Heating elements, water lines, T&P valves, and other components can be replaced, but once the tank begins leaking the water heater will need to be replaced.

Manufacturers have several preventative measures to help protect from corrosion. The first is the anode rod, which is a round, long piece of metal that’s installed within the tank. Its role is to sacrifice itself to prevent the tank from corroding.

The second line of defense is the tank lining itself. Manufacturers use different types of linings to protect their tanks from corrosion. Two of the most common tank linings are porcelain enamel glass lining and glasslined coated, but there is also vitreous enamel coated and blue silicon enamel coated tanks.

The inner surface of the water heater’s tank is fused with a glass coating to provide protection from corrosion. As a general rule, polymer coatings tend to add better protection than glass lined tanks, but if you replace your anode rod as needed and perform regular maintenance you can help protect the lining of your tank, and ultimately the service life of your water heater.

Energy Efficiency 

Smaller water heaters, like the 20-gallon units are not as energy-efficient as larger sized units. However, that doesn’t mean you shouldn’t look for features which can help with efficiency. Insulation and the material used to manufacture the water heater can all play a factor.

Look for water heaters that use foam or fiberglass insulation. Some units will provide you with an R rating to help you determine the effectiveness of the insulation. An R-22 or higher rating for electric water heaters is ideal. But you can always wrap the heater in a water heater blanket to help reduce standby heat loss and ultimately improve its efficiency. 


Reviewing the warranty is always a good idea when shopping for a water heater. A good warranty for smaller water heaters is roughly six years, but take a look at the fine print so you know what the warranty actually covers. Most warranties have limits. It’s not uncommon to see warranties that’ll offer longer coverage on parts, and shorter coverage for labor.

As a general rule, you can expect to pay more for a water heater with a longer warranty, but you’re also buying a higher quality product. 

SIze And Water Capacity

Due to their smaller capacity, 20-gallon water heaters are used in mobile homes because they fit everywhere easily. Just remember that a mobile water heater cannot be installed anywhere and there are many differences with standard water heaters.

Because of their small size, 20-gallon water heaters are often an excellent choice for mobile homes. According to the Seattle Times, mobile homes have to use every available space, which means when it comes to a water heater, it may be behind a panel inside the wall, in a closet, under the sink, or be hanging on the wall. 

American Standard CE-20-AS

While classified as a 20-gallon water heater, the American Standard CE-20-AS actually has a 19 gallon tank. It runs on electricity and has a heavy gauge steel tank lined with Dura glass. It comes with a brass drain valve and a brass temperature and pressure relief valve which adds durability.

The CE-20-AS is one of the best selling American Standard water heaters, and it’s a perfect size to fit into small tight spaces. It uses 110 volts of electricity and can regenerate hot water in about 30 minutes.

One helpful feature about this heater is the water hook-ups. The hot and cold water hook-ups are located on both the side and top of the unit, which gives you the option to use the set that works best for your unique installation set-up.

American Standard is a well-known and respected name in the water heating industry, and takes great pride to ensure their products meet the highest quality standards. The CE-20-AS comes with a six-year limited tank and parts warranty.

  • Steel tank with Dura glass lining
  • Brass valves
  • Energy cut-off system
  • Adjustable thermostat control up to 160°F
  • Side and top water hook-up options
  • Dimensions: 18.5″ x 18.5″ x 24.88″

A.O.Smith EJCT-20

The compact A.O. Smith EJCT-20 has side-mounted plumbing and electric connections for easy installation. It also features a tamper-resistant brass drain valve to prevent accidents, and has a Coregard anode rod to help protect against corrosion.

The heater has an R-rating of 8, which is on the low side, but it’s capable of producing 11 gallons of hot water per minute. The tank is glass lined and the unit runs on 120 volts of electricity and comes with a limited six-year warranty.

A.O. Smith is a top name in the industry and is known for efficient and reliable products. The company has been around since 1874 which makes it one of the oldest companies in the hot water heating industry.

  • Side-mounted plumbing
  • Brass drain valve
  • Coregard anode rod
  • Dimensions: 16″ x 16″ x 31-5/8″

Rheem PROE20 1 RH POU

The Rheem PROE20 1 RH POU water heater uses an electric 120 volt power source and has an optional wall mounting bracket for additional installation options. The unit meets or exceeds the requirements of the National Appliance Energy Conservation Act

Rheem uses their proprietary Rheemglas tank lining to add durability and improve the heaters energy efficiency. In addition, the unit comes with a stainless-steel heating element, brass drain valve, and premium grade anode rod, all of which will add to the durability of the water heater.

An over-temperature protector cuts off power should the water heater reach excessive temperatures, and an automatic thermostat ensures your water is always the right temperature.

The Rheem 20 gallon water heater produces an impressive 17 gallons of hot water per hour and comes with a six-year warranty on parts and a one-year warranty for labor.

  • Rheemglas tank lining
  • Brass valves
  • Side connections 
  • Optional wall-mount
  • Dimensions: 16″ x 16″ x 20″

Stiebel Eltron 20 Plus PSH Wall Mounted, Tank, Water Heater, White

The Stiebel Eltron 20 Plus is a wall-mounted electric water heater that’s designed to save space. It has a sleek, quality finish that looks great even when installed in a visible location. The control knob is located on the front of the unit to allow for easy operation.

 It’s an electric water heater that runs on 240 volts, with a first-hour rating of 30 gallons. This among other things, make this one of the best performing water heaters of it’s size on the market.

The 20-gallon water heater comes with an optional drain pan that can be mounted on the wall under the unit. Operating on 240 volts of electricity, the water heater has an impressive FHR of 30 gallons, which means you can expect 30 gallons of hot water during the first hour of usage.

The Stiebel Eltron 20 Plus features a CoPro glass enamel lining and polyurethane insulation, and has a magnesium anode rod. It regenerates hot water in less than 30 minutes so you’ll always have hot water available.

Stiebel Eltron is known for quality workmanship and the company backs this water heater with a six-year limited warranty.

The Stiebel Eltron 20 Plus has a CoPro glass enamel coating that helps improve it’s efficiency, which is essential in these smaller units in order to provide a continuous flow of hot water, while minimizing heat loss. The company backs this up with a built-in polyurethane insulation to boost heat retention even more.

One of the unique features of this water heater is the fact that its designed to be mounted on a wall. If you want to save space, mounting your water heater on the wall is the way to go. It even has a stylish finish that makes it look sharp where ever you have it installed.

  • Wall mounting saves floor space
  • Quality finish. Elegance to suit every environment and decoration
  • Powerful electric element provides plenty of hot water and long service
  • Factory installed adjustable temperature control for safety and comfort
  • Temperature control located in front for easy access
  • Magnesium anode rod
  • CoPro glass lining
  • FHR 30 gallons
  • Included drain pan
  • Dimensions: 20.5″ x 20.5″ x 34.25″

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BY M. Kogan

Hello, I am Marcio. I am an architect and designer, alma mater is Mackenzie. Retired in theory, but an architect never retires completely. Along with architectural projects, I am a filmmaker and have completed some short documentaries. Filmmaking and design are my passions. In HomeQN I write about home decoration and foundations. The goal is to teach homeowners to DYI as much as possible, and when this is not possible, enable them through knowledge, to evaluate service quotations and choose the best service technicians.

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