Choosing a water heater of the correct size will help you cut down on electricity bills while enjoying an ample supply of heated water for your home. How you size a water heater will depend on the type of heater that you buy.
If you plan on buying a demand or tankless water heater, you’ll first need to determine the flow rate and temperature rise required to provide sufficient water to your home. You can calculate the flow rate by making a list of all appliances in your home that use hot water and noting how many gallons of water each appliance uses per minute. Add all of these flow rates up to determine the minimum flow rate needed for your home.
Then, subtract the temperature of the incoming water from the desired water temperature. If you don’t know the input temperature, assume it is 50 degrees. Subtract 50 degrees from the maximum temperature to which you need water heated. This is the temperature rise needed for your home. Look for a water heater that meets both your flow rate and temperature rise needs. A professional plumber can easily make these measurements for you when you decide it is time to purchase or replace a water heater.
If you want to buy a solar water heater or a traditional, tank-based model, ask a plumber or HVAC contractor to help you with sizing calculations. Your contractor will be able to manipulate calculations to meet your efficiency needs.