Notes - Heat pumps do not make heat, they capture heat from the air and transfer it to the pool water using a refrigeration circuit (like Refrigerators or Home Air Conditioners). The COP or COEFFICIENT OF PERFORMANCE of the heat pump is the ratio of heat provided to the energy required. Heat pumps are an energy multiplier (eg: a COP of 6.0 means that for every watt of electricity used, 6.0 watts (or 20.472btu) of heat are transfered to the pool). The higher the COP, the lower the cost per BTU. Heat Pump COP and BTU vary with Outside Air Temperature, Outside Humidity, and Pool Temperature. Heat Pump BTU output relates to how fast it will heat a pool and how much water a given heat pump can keep warm due to heat losses. Heat Pump COP increases as ambient temperature and humidity increase. Water Flow rates and temperatures also affect the heat transfer rates.