Geothermal Heat Pumps Basics

What is a heat pump?

Heat normally flows from hot to cold just as water flows downhill from high to low. Heat pumps move heat "uphill" against this normal flow.

  • A refrigerator is a heat pump. It moves heat from inside the fridge to the surrounding room so food stays cold.
  • Air conditioners are also heat pumps, moving heat from indoors to outdoors.

What is a 'geothermal' or 'ground source' heat pump?

A geothermal or ground source heat pump heats or cools your home by moving heat to and from the ground through a series of buried loops. A "desuperheater" can be added to a geothermal heat pump to provide water heating.

Ground loop (vertical and horizontal) configurations

Illustrations of the two most commonly used group loops

What are the advantages of geothermal heat pumps?

  • Low noise - no outdoor equipment above ground.
  • Very efficient as air conditioners.
  • No on-site combustion.
  • A single system can provide heating and air-conditioning (and optional water heating).
  • If electricity generation becomes cleaner, geothermal heat pumps could have clear-cut environmental benefits compared to natural gas furnaces.
  • Available installation incentives:
    • Federal tax credits through 2016
    • Focus on Energy cash-back rewards (for most Wisconsin homeowners)

What to consider before choosing a geothermal heat pump?

  • Higher installed cost than traditional heating systems (tax credits and incentives can reduce cost).
  • Expected energy cost savings may not be achieved.
    • The price of natural gas and electricity has a big effect on savings. At $1.00 per therm for natural gas and 14¢ per hour for electricity, a 92% efficient natural gas furnace costs about the same as a geothermal heat pump to produce the same amount of heat. Heat pumps compare more favorably to propane and fuel oil because these fuels typically cost more than natural gas.
    • Compare different scenarios using this Heating Fuel Comparison Calculator from the Energy Information Administration [123 kB XLS].
    • Call MGE's Home Energy Line at 252-7117. We'll do the comparison for you.
  • Geothermal heat pumps are more complex than typical heating systems.
    • System design and installation require much more expertise and care.
    • Oversized pumps, improperly sized and installed ground loops or other installation problems can increase electricity use of a heat pump system, increasing your costs.
    • Ground loops need to be designed and installed properly.
  • If backup electric heat is installed, it can be costly to operate. To avoid high bills, understand when the electric backup heat comes on.
  • Some soil types work better than others. Wet, dense soils conduct heat better.
  • Expected environmental benefits might not be achieved.
    • Because geothermal heat pumps use electricity, the fuel used to generate your power determines the environmental impact. Most of the electricity used in Wisconsin is generated by burning coal.
    • A 2009 analysis by the Energy Center of Wisconsin found: "In the residential and community/multifamily scenarios, CO2 emissions generally remained constant or increased slightly with inclusion of a geothermal heat pump system."

MGE recommends:

  • Compare alternatives (such as a high-efficiency gas furnace), especially if natural gas is available.
  • Compare environmental claims carefully.
  • Contact the Wisconsin Geothermal Association for a list of experienced professionals.
  • Make sure your home is well insulated and air sealed, with good ventilation regardless of what type of heating system you choose. If your new home doesn't require much heat, the type of heating system you choose becomes less important.
  • If the building is new, see MGE's New Home Planner [3.1 MB PDF] for recommendations.

For more information