Heat pumps are simply air conditioners that can go in reverse. A standard air conditioner pumps heat from inside your house to outside. Heat pumps have the ability to do that as well as pump heat from outside into your home. In Wisconsin these systems can be useful in the transitions between seasons in the spring and fall when heating and cooling may be necessary. However, it is usually required to have some sort of back-up heat for those real nasty winter days and nights.