What Size Water Heater Do I Need (Expert Q&A)


It is important to understand what size of water heater you need because they consume around 25% of your energy costs. Do you want tankless or tanked? Do you want an electric water heater or a gas water heater? Standard electric heaters are often less expensive than gas but as a benefit, gas heaters remain on if there is an outage.

Traditional Tank Water Heaters

Also called “storage” tank water heaters, traditional tank water heaters are installed in most residential homes. As its name applies, storage tank water heaters include an enclosed tank that heats the waters and stores it for use later. The heated water, when needed, flows out of a delivery pipe that extends out of the top of the heater.

Storage water heater tanks are equipped with a pressure-relief valve and a temperature valve. Here are storage and capacity data for the storage tank:

  • Water storage: between 30 and 100 gallons of hot water
  • Water capacity: 70% usable capacity (i.e., if your water heater is a 50-gallon tank, then you will be using 30-35 gallons of hot water.

The storage tank water heater fits perfectly in large appliance-active residential homes. The life span for an electric water heater can last up to 13 years. The life span for a gas water heater is close to the same number of years.

Traditional storage water heater tanks average 5′ or taller and around 2′ wide or wider. If your storage water heater will be located in a basement, then yes you have the space for its installation. Uncle Sam has not helped to decrease the size of storage water heaters.

The federal energy regulations have required that new tanks use more insulation. Storage hot water heaters that hold less than 55 gallons are the smaller sized tanks and tanks that hold 55 gallons or more will be larger, depending on the energy-saving model you choose.

Tankless Water Heaters

Tankless water heaters are “on-demand” water heaters because they provide instantaneous hot water as you need it. Unlike traditional or storage tank water heats, the tankless water heaters do not hold or store water.

Instead, tankless water heaters are designed with heating coils or gas burner that heats the water. They can supply 2 to 3 gallons of hot water per minute which means the tankless water heater will deliver an unlimited supply of hot water.

Tankless water heaters save you money and are the most energy-efficient model of water heater because they restrict the water output allowing them to handle high-demand water usage. Tankless water heaters have a lifespan of more than 20 years. They are also available in an electric model, a gas model, and a propane model.

An electric tankless water heater is of a different design than the gas models. The gas water heater models can burn both natural gas and propane. Choosing gas, electric or propane tankless water heaters will depend on how much hot water your home needs, your budget, and your installation options.

They are small enough to fit into any space or they can install on a wall. Tankless water heaters are a popular style for residential homes, laundry facilities, hot tub users, public restrooms, eco-friendly, and they support today’s solar water heating environments.

Electric tankless water heaters do not require venting, but the gas tankless water heaters do require venting installation. Gas tankless water heaters should have an annual maintenance check, but electric tankless heaters do not require annual maintenance.

Point-of-Use or Utility Water Heaters

Point-of-Use water heaters are small or boutique style storage tank water heaters that range from 2.5 to 19 gallons of water. They are small enough to be mounted on a wall very close to the fixtures where hot water is needed in the immediacy like a sink, a shower/bath, a hot tub, or a restroom that may be in a garage or a basement.

Point-of-Use or utility water heaters are not your central water heater models. However, they are best used close to where the hot water supply is required. Utility or point-of-use water heaters use less than 20 gallons per day and as an extra hot water device, it will save you money and energy.

For utility water heaters and its water usage at limited locations, you will probably only need the amount of hot water that it stores within its tank. Many homeowners enjoy matching their point-of-use water heaters in-line with their main water heater system so that there is no wait time for hot water within the plumbing system.

How Many Gallons Do You Use?

For a good guestimate about what size water heater you may need. Plumbers and electricians provide the following simple capacity data based on the number of people in a home and their water usage:

  • 23 – 36 gallons: 1 to 2 persons
  • 36 – 46 gallons: 2 to 3 persons
  • 46 – 56 gallons: 3 to 4 persons
  • 56 and more: 5 and more persons

Remember that the more hot water your household needs, the more BTUs and capacity you’ll need.

Wash, Brush, Flush

There is a common data thesis that is provided by utility companies and institutions that give you a quick idea of household water usage. Here are daily living factors that will help you decide what size hot water heater that you will need:

  • a dishwasher uses 6 gallons or less for each use
  • showering uses around 5 gallons per minutes
  • bathing in a full tub uses around 36 gallons
  • shaving the face and other body parts uses about 1 gallon if you don’t keep the water running
  • washing your hands uses from 1 to 2 gallons with water running
  • cooking uses 4 gallons
  • a washing machine uses around 7 gallons

Now for the best feature in a restroom – the toilet. Most of the toilets use approximately 1.5 gallons of water for each toilet flush. However, today’s toilet water tanks can be adjusted as follows:

  • ultra low flush toilets: 1.6 gallons per flush which is a federal law
  • high-efficiency toilets: 1.3 gallons per flush
  • dual-flush toilets: an average flush is 1.1 gallons or less for both a full flush and a half flush

Final Note

As you can see, determining a water heater size for your home is a math quiz. We haven’t even gotten to first-hour rating and peak hour demands. I guess what I am saying is that your friendly plumbing professional can help you make the determination as to what size water heater is best for your household and your budget.

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