What Does It Cost To Heat Your Water?
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).
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 a 80°F rise.
Heating a gallon of water thus requires 8.33 x 80 = 667 Btu’s, at 100% efficiency.
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 of water!
Cost To Heat Water Using Electricity?
A typical electric water heater is 90.4 to 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!