It is generally accepted that it costs about 1¢ to 2¢ to heat a gallon of water. The exact amount will depend on the efficiency of your water heater, whether you use gas or electric and exactly what your electric or gas costs are.

# Energy Required To Heat 1000 Gallons Of Water

- A BTU, or British thermal unit, is the amount of energy needed to raise one pound of water from 60°F to 61°F at sea level.
- A gallon of water weighs 8.33 lbs.
- If the incoming water is 60°F and we want to raise it to 140°F, that is an 80°F rise.
- Heating a gallon of water thus requires 8.33 x 80 = 667 BTU’s, at 100% efficiency.

# Cost To Heat Water Using Natural Gas

- A typical gas tank water heater is only 59% efficient. It takes 667 ¸ 59% = 1131 BTU’s to heat a gallon of water with gas.
- One therm is 100,000 BTU’s. One BTU is 0.00001 therms.
- 1131 BTU’s is 0.0113 therms.
- It will take 0.0113 therms to heat a gallon of water, or 0.0113 x 1000 = 11.31 therms to heat 1000 gallons.
- At $1.20/therm, it costs 11.31 x $1.20 = $13.58 to heat 1000 gallons.

# Cost To Heat Water Using Electricity

- A typical electric water heater is between 90.4% and 95% efficient or 92.7% average efficiency.
- It takes 667 ¸ 92.7% = 720 BTU’s to heat a gallon of water using electricity.
- One kWh is 3413 BTU’s. One BTU is 0.000293 kWh.
- 667 BTU’s x 0.000293 kWh/BTU = 0.195 kWh
- It will take 0.195 kWh to heat a gallon of water, or 0.195 x 1000 = 195 kWh to heat 1000 gallons.
- At $0.11/kWh, it costs 195 x $0.11 = $21.45 to heat 1000 gallons of water.