how many btu to heat a pool
Rules For Sizing Your Heat Pump Pool Heater. 1  Size at 4 BTUâs per gallon or 1 BTU per litre of water. To heat in normal summer conditions when ambient air temperature average 70Â°F in a 24 hour period.  Size at 5 BTUâs per gallon or 1.3 to 1.5 BTUâs per litre of water.