I made a calculation last year with the rates in Ontario and my natural gas heater costs something like $3/hr to run... it's a 250k btu hayward and with a ~20k gallons pool (if I remember correctly), it raises the temperature by just a bit more than 1 degree / hour.
Here's the calculation I had sent to a friend and why a pool cover was needed:
Here's the calculation I had sent to a friend and why a pool cover was needed:
2.77m3 of gas = 100,000 btu, so roughly 7m^3 of gas every hour.. and each m^3 = ~$0.30 which means $3 / hour to operate the heater.
let's say that you need to raise the temperature of the pool by 15 degrees:
8.3 btu are needed to raise 1 gallon of water by 1F, so for 20k gallons * 15 degrees, it's a 2.5M btus needed and the heater is 80% efficient, so 3.1M btu are needed. 3.1M btu = 86m^3 of gas.. so ~$25. if you raise it by 20 degrees F it's $32. I guess that's not too bad.. but add thermal loss and I'm sure the number shoots up.
thermal loss: for low wind, ~7 btu / sq ft per hr per degrees F difference between water & air.. at night, let's assume 20 degrees (water at 85F, night = 18C). So for a 500 sq ft pool, it's 7 * 20 * 500 * 12 (12 hours) = 840k BTU every chilly night that you lose.. so $7 per day just to compensate for the loss. ouch. if it gets windy, it's even worse.