Swimming Pool Heat Losses
In order to maintain a heated pool at a given temperature, a heater must replace as much heat as the pool loses. Pools lose heat in four ways:
EVAPORATION - for every gallon of water that is evaporated, approximately 8000 BTU is taken with the water vapor from the pool. This usually amounts to 50 to 95% of ALL losses. 50% IF COVERED AND UP TO 95% IF UNCOVERED
CONVECTION- heat is lost to the air as it passes over the pool - this can usually account for 10 to 50% of the total heat loss.
RADIANT COOLING- heat is lost by the warm water as it gives off infrared radiation back to the sky especially at night. Cloud cover will reduce this effect but the atmosphere will still absorb and scatter this thermal energy like light waves. This may account for 5 to 15 % of all heat loss.
CONDUCTION- heat lost directly to the ground. Initially when a cold pool is being brought up to temperature, the ground and concrete or vinyl liner walls will absorb some heat. After they warm up, the soil around the pool actually insulates it slowing down the heat transfer to a minimal amount compared to total heat losses. Usually ground losses are negligible or less than 2% of all heat loss.
HEAT SIPHON FAST FACTS - In the typical 15 x 30 foot pool (450 sq ft) an inch of water has a volume of approximately 280 GALLONS so for every inch of water that evaporates your pool will lose 2.25 MILLION BTU's. One BTU (British Thermal Unit) is the amount of heat it takes to raise the temperature of 1 pint of water by 1°F.