Pools can be heated with a GHP and in very warm climates, this makes a good match with a space conditioning GCHP. In cooling dominated climates, the space conditioning heat pump rejects much more heat to the ground than it absorbs from the ground. As a result, there is the potential for a gradual increase in ground temperature to occur over a period of years, where a ground-coupled system is used. Removing this excess heat and delivering it to a swimming pool reduces (or eliminates) the problem.
Pool heating will require a separate heat pump for the pool. Beyond this, the heating capacity of the heat pump will likely be less than that of a typical gas-fired heater in the same application. This is a result of the fact that heat pumps cost about five times what gas-fired pool heaters do per unit of heating capacity. The smaller heat pump would not affect the ability to maintain pool temperature, but would result in a longer time required to bring the pool temperature from cold up to usable temperatures at the beginning of the season.
The pool heating unit would be of the water-to-water type rather than the water-to-air design used for home heating and air conditioning. The impact of the pool heating upon required loop length would depend upon the size of the pool and the amount of the year it is in operation.