Geothermal Heat Pumps
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
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.
- Call MGE's Home Energy Line at (608) 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."
Before you buy a heat pump
- 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 for recommendations.
Why is further geothermal heat pump research needed in cold climates?
The measured performance of geothermal heat pumps in cold climates in studies that we are aware of suggests that heat pump systems don't work as efficiently as people would expect. We also have heard from customers who have geothermal heat pumps and are unhappy because they see higher heating costs than they expected.
Help MGE learn more
Know of a house that's switched from a natural gas to a geothermal heat pump in MGE's service area? Please call us at (608) 252-7117 with the address! We're particularly interested in comparing heating costs before and after the geothermal heat pump was installed.
Resources and further reading
- These two cold-climate field studies found that measured performance is lower than the performance ratings published by manufacturers. (Similar to the way real-world mileage differs from the mileage-rating stickers on cars).
- Energy Center of Wisconsin analysis says modeled dollar savings and environmental benefits are small for residential geothermal heat pumps.
- Building Science Corp. Digest #113: "This digest provides some basic information and definitions, offers advice on how to compare the carbon emissions, and defines the climate regions and operating conditions for which (geothermal heat pump) systems are best suited." And, "There has been a recent surge of interest in Ground Source Heat Pump (GSHP or "geothermal" or GeoExchange™) systems for residential projects. Outrageous claims and misunderstandings about how they work are common."
- Green Building Advisor article.
- Minnesota Sustainable Housing Initiative article.
- Dept. of Energy Geothermal Heat Pump information.
- A geothermal heat pump "survival kit" including economic comparisons. Published in 2001, it still has useful information.
- The Wisconsin Geothermal Association promotes ground source heat pumps and publishes "How to Choose a Pro."
Federal tax credits may be available.