Here is a way to determine how long it will take your heater to heat your pool water, and how much it will cost you if you are using an electric heater.
This of course won't tell you how much it costs to keep the temp at a certain level once warm, but it will give you an idea as to how long it will initially take to heat the pool.
This is based on my in-ground pool, but you can figure in the parameters of your individual pool to get your correct numbers.
Be advised .. This is only an estimate .. These calculations only reflect the required heating of the water, and do not take into consideration the heating of the cold pool walls or any associated equipment in the pool.
If you don't agree to these calculations, please feel free to respond.
9,000 Gal. Gunite Pool
104,000 BTU Electric Heat Pump (5.5 KwH power consumption)
Determine Time Required to Increase Water Temp 1 Degree F:
1. Multiply the total gallons of water in the pool by 8.3
This will give you the total weight of the water
(9,000 gal x 8.3 = 74,700 lb)
2. Divide the weight of the water by your heater's BTU
This will give you the hours it takes to raise the water temp 1 degree F
(74,700 lb / 104,000 BTU = .72 hrs)
Determine Total Time Required to Increase Water Temp the Desired Amount:
1. If the current water temp is 65 degrees and you want to raise it to 80 degrees (15 degree increase) ..
Multiply 15 degees by the time it takes to raise the temperature 1 degree F
(15 degrees x .72 hrs = 10.8 hrs)
Determine the Cost of Electricity you Will Use:
1. If your heater uses 5.5 KwH, and with a 10.8 hr run time, it will use 59.4 KwH of electricity
(5.5 KwH x 10.8 hrs = 59.4 KwH)
2. Using 59.4 KwH, and a cost of electricity in your area of 12 cents per KwH, it would cost $7.13
(59.4 KwH x .12 cents = $7.13)