a pool heater is probably about the same as what you are talking about and basicly they work very much like an A/C/system only in reverse. a heat pump to cool/heat a home has a valve (reversing valve) that does just that when in coolong mode you will feel hot air blowing out of the condenser (outside unit) and when in heat mode you will feel cold air from that unit. there is all the things that are in an A/C/ system, just all contained in one pkg. i think it going to depend on how cold the water is to start because you usually only get about a 20 degree f difference at best??
