A geothermal furnace is a heat pump that uses water instead of air as a source of heat gain or loss. Water is pumped through a closed loop of pipes buried in the ground, or pumped from a well and discharged into another well or into a pond. The condenser and evaporator coil are enclosed in one cabinet. A backup electric heating element may be installed in the supply ductwork

In heating mode, heat is extracted from water as it passes through the condenser, and released through the evaporator coil.

In air conditioning mode, heat is extracted from the evaporator coil and released into water through the condenser.

Accessories can include; an air filter, electronic air cleaner , high performance media filter, and a humidifier. The humidifier can be of the steam generating type, which will be line voltage powered, so caution must be taken to shut off power before servicing. Sometimes a condensate pump will be used to dispose of the water produce in the dehumidifying action of the air conditioning.

If the system is zoned, a zone control panel and motor actuated dampers will be installed on the unit or in the ductwork.

A filter or strainer may be installed in the supply side of the water feed to keep sediment out of the pump and condenser if drawn from a well.

Routine maintenance includes replacing the air filter or washing the electronic air cleaner grids, cleaning the humidifier, and servicing the water filter or strainer. All maintenance should be done with the system shut down.