The geothermal unit indoors: types, sizing and placement
The geothermal unit is the indoor cabinet that holds the compressor, the refrigerant circuit and the heat exchangers of a ground source system. It takes heat from the ground loop and passes it to the house as warm air or warm water, and in summer it runs in reverse for cooling.
What does the geothermal unit do?
A geothermal system links the ground and the home through this cabinet. On one side a heat exchanger receives the loop fluid, and on the other side a second exchanger or coil delivers heat to the distribution system. In between, the compressor and a refrigerant circuit lift the temperature, using the cycle explained in how ground-source heat pumps work. Controls, a reversing valve and a few safety devices round out the cabinet.
It looks like a furnace-sized box, but it replaces both the furnace and the air conditioner, and the geothermal system uses less energy for heating and cooling. The full list of components is in the geothermal HVAC system parts guide.
Which types of indoor unit exist?
- Water-to-air. Heats and cools the house through ducts. It suits homes with a forced-air system and often contains the blower and the air coil.
- Water-to-water. Produces warm or chilled water for floor heating, radiators or a hot water tank. It suits low-temperature hydronic systems, as described in low-temperature hydronic heating.
- Packaged and split. A packaged unit holds everything in one cabinet, while a split unit separates the air handler from the compressor section and can fit awkward spaces.
- Staging. Single-stage, two-stage and variable-speed compressors differ in comfort, noise and efficiency. Variable speed matches output to the load.
How is the unit sized?
Capacity comes from the heat loss calculation for the house, not from floor area. A geothermal heat pump that is too big cycles on and off and wastes the benefit of the ground, and one that is too small leans on backup heat in cold weather, which hurts energy efficiency. The method is in heat pump load calculation. The size of the loop and the size of the geothermal system must also match, since the loop supplies the heat the system uses. Ask the installer to show both calculations, and the cooling load as well.
Where does the unit go?
Most geothermal units are in a basement or a utility room, close to the ducts or the manifold of the floor heating, and close to the point where the loop enters the building. The room needs enough space for the unit and service clearance on the sides the manual specifies, a drain for condensate, and electrical supply of the right size for home use. The geothermal unit makes some sound from the compressor and the blower, much less than an outdoor air-source unit would outside the window, but a location away from bedrooms still helps. For a comparison, see heat pump noise levels.
Check the path for the loop pipes and the access for replacing the geothermal unit later. A cabinet squeezed into a closet is hard to service.
How long does it last and what does it need?
The indoor cabinet is the part with moving parts and wears like other heat pumps, while the buried loop is expected to last much longer. The ground source heat pump lifespan guide separates the two. Ongoing care is modest: replace the air filter, check the condensate drain, and have the geothermal system serviced on the schedule in geothermal heat pump maintenance. A desuperheater, if fitted, uses spare energy to heat water and adds a small pump and a water connection that need an annual look.
Quick answers
What is the indoor unit of a geothermal system called?
It is called the geothermal heat pump or the geothermal unit. It holds the compressor and heat exchangers and connects to the ground loop and the distribution system.
Does a geothermal unit replace my furnace?
Often yes. A water-to-air unit with a blower can heat and cool through the existing ducts, and some homes keep a small backup heater.
How big is a geothermal heat pump unit?
Residential units are commonly about the size of a furnace or a large appliance, but sizes vary by capacity and type. The manual lists the dimensions and the clearances.
Is a geothermal unit noisy?
It is generally quiet, since there is no outdoor fan. Placement away from bedrooms and good mounting reduce what you hear.