In winter, with the heating mode, the desuperheater heats a portion of your hot water. Desuperheaters are standard on some units, optional on others. Stand-alone systems which will heat water all year around can be purchased. Called dual systems, they can easily be added to existing furnaces for those wishing to have a dual-fuel heating system. Dual-fuel systems use the GHP system as the main heating source, and a fossil fuel furnace as a supplement in extremely cold weather should additional heat be needed.
All systems require an emergency back-up.
Heat pumps can provide all the heat necessary even in the coldest weather. An economic analysis by your contractor should dictate what portion of the heat should be provided by the heat pump and which by auxilary means. GHP systems are generally sized to meet all your cooling needs. Sizing the system to handle your entire heating needs may result in slightly lower heating costs, but the savings may not offset the added total of the larger system. Special consideration should be given to systems in the north where multiple capacity units should be considered to handle the large variation between heating and cooling loads.