How to Size Hot Water Heaters

Properly sizing the hot water heater for your home is a crucial task that ensures that you'll have hot water whenever you need it. To do so, you'll need to take a close look at when and for how long the people in your house use hot water. Hot water is measured by the amount produced per minute. The more hot water you need at one time, such as someone showering while a load of clothes is being washed, the bigger your hot water heater will need to be.

An inproperly sized hot water heater can lead to a cold shower.
  1. Pay close attention to the tank size. The size of the hot water heater largely depends on the size of the tank. Tank size determines how much hot water is available at one time and can range from about 20 to 120 gallons.

  2. Figure out approximately which size you require for your home and hot water needs. For example, a one bathroom house might need between a 30- and 40-gallon tank, while a one and a half bath home would need at least a 40-gallon tank. A three and a half bath home needs more like a 66- to 80-gallon tank. According to Don Vandervort's Home Tips, 75- to 120-gallon tanks are usually needed for homes with four bathrooms or at least one extremely large bathtub.

  3. Research the difference between gas and electric hot water heaters. Generally, gas hot water heaters measure capacity in BTUs, and electric models measure capacity in watts. A 75 gallon gas hot water heater is approximately the same as a 120 gallon electric heater because gas heaters can heat the water more quickly.

  4. Utilize online resources to help you determine the exact size hot water tank you need by figuring out how much hot water your family needs at one time. Sizing calculators are available online (see Resources). Here, you will determine how many gallons per minute of water are produced by each appliance in your home, determine which of these appliances tend to be in used within the same time frame and combine both to produce the amount of total gallons per hour that is needed.

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