How to Calculate the Best Size for a Water Heater
- 1). Determine the number of people that will be living in the house.
- 2). Add one to the number of people living in the home.
- 3). Multiply the number found in step two by 12. For example, if you had five people in the home, you would add one to get six, and then multiply by 12 to get 72. This is the minimum FHR that your water heater should have, according to the National Appliance Energy Conservation Act.