Geothermal Myth #2: My Geothermal Unit Will Need a Backup

This myth is completely reliant upon appropriate sizing of your geothermal unit. Sizing is one of the most important factors when installing a geothermal unit which is why it is essential to use a qualified geothermal contractor. An undersized system will not only require a backup unit but it will rely heavily on the backup unit during extreme temperatures. Constant use of a backup unit will end up costing you even more than traditional heating and cooling solutions.

If you have a correctly sized unit, you do not need a backup system. Geothermal unites are equipped with an auxiliary heating unit that runs on electric. This backup system does not exist as a supplemental heat source for extremely cold temperatures; it is only in place to serve as a precaution in the rare instance that your geothermal heat pump breaks down.

By utilizing the constant temperature in the ground a geothermal heat pump does not need a backup radiator or furnace as supplemental heat on extremely cold days. Myth #2 is put to rest; geothermal heat pumps do NOT need a backup heat supply.

Myth #1: Geothermal Heat Pumps Don’t Work in the Extreme Cold

Check back for Myth #3: I can’t afford a geothermal heat pump system

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Comments (12)


  1. Jacqueline Gauvin says:

    That has not been my experience. When the temperatures drop below 20, we have to use space heaters and our fireplace insert to stay warm. Even worse, I have learned that here in Michigan, no heating contractor will work on a geothermal system unless they installed it. If the heat goes out (which it has twice in the the six years I have had the system) I have to wait until the contractor who installed the system is available to come out and work on it. I would not recommend this system to anyone else.

    • Mara says:

      My experience, sadly, has been similar to that of the other posters- we live in suburban DC and the system cannot keep up even when temps are in the 30s, let alone 32 and below. Even with the auxiliary electric heat on, which is a constant, the house is uncomfortably cold. We also rely heavily (and dangerously) on space heaters and heating pads (to warm beds before climbing in). The company that installed it cannot seem to figure it out, and others I’ve called seem reluctant to come look.

  2. Steve Radcliffe says:

    I’m glad to see this myth busted. I wonder though. I live in Chesapeake, VA and have a 5 ton, 2 stage FHP that can’t keep up in very cold weather. No one is freezing, but asking for 68 and it taking all day to get it says something is amiss. I’t 1:22 PM, 22 degrees outside and the downstairs temp is 66. Loop water temp is around 50 degrees. We began the day at 13 degrees. It’s been asking for 68 since 8 AM or so. The house is about 2400 sq. ft. Filters are all clear so what should I be looking for?

  3. Tom Barton says:

    It may well be that my geothermal system is undersized, but whatever the cause, the unit needs to go to the alternative electric heat source quite often when it is extremely cold and windy here in Iowa. This of course results in huge electric bills, negating the economies of the heat pump system. My question is whether anyone has developed a natural gas alternate heat source to be combined with the geothermal?

  4. Roger T. says:

    Hello and thank you for your blog!
    I had a closed loop geothermal system (Bosch) installed in my 3400 sq.ft. home in the middle TN area in July of 2015. The cooling for that hot month and the rest of the summer season was pretty good on the pocket book….
    Then comes our first electric bill for the month of Nov/Dec 2015 and it was twice the normal. We expected an increase due to changing from propane heat to all electric (geothermal). I woke up last night and checked the thermostat and it read “auxiliary heat”, the outdoor temp was 30 degrees F.
    Here’s the issue the I am really wondering about; my installer attached an outdoor thermostat to my unit and set it at 40 degrees, much like a air transfer heat pump. He said that it was needed for the auxiliary heat if the indoor temp fluctuated 2 degrees F. The temp in the house did not fluctuate whatsoever and remained at 68 degrees with the blower running almost non-stop. In the early morning I pulled the outdoor thermostat sensor back through the wall into my heated basement and the auxiliary heat turned itself off and the unit ran normally.
    Question is: does geothermal need this type of thermostat or did he hook it up like a conventional heat pump and is it ok to continue without it? Your observations are much appreciated.

  5. Anthony Kaiser says:

    You all need to file lawsuits with your installers, They short-sheeted your geo system, either to meet a price-point, or because they didn’t know what they were doing designing an under-capacity loop system.

  6. Mike says:

    I built a new house in 2009 which included a geothermal system. My experience has been that Michigan winters having consecutive days below 20 degrees will have the geo system calling for auxiliary heat. This only started happening once we finished off the basement where before we were able to keep the basement door closed. I will be looking into adding a boiler for hot water and supplement the geothermal system.

  7. Carol Seidlich says:

    We have 2 systems, one is a 2.5 ton operating on an open loop to heat 2nd level; one 2 ton operating on a closed loop for the 1st floor, in all @4000 sf. The closed loop is 2 yrs old. We separated units as both could not operate on the open loop and the condenser failed for 1st fl unit. Auxiliary heat comes on for 1st floor unit and shows loop is 36 degrees. A new well was dug for new unit. I experienced this with both units on open loop. By separating units I expected no auxiliary heat issues. Why would the loop temp be so low. Does the ambient water temp go down that much?

  8. Eric Makkay says:

    This is misleading. You will have one geothermal unit for both heating AND cooling. Depending on where in the country you live, it is highly unlikely your geothermal unit will be perfectly sized for BOTH heating and cooling. You will inevitably be some combination of correctly sized/undersized/oversized. My unit is correctly sized for cooling and undersized for heating in New Jersey so auxiliary heat is needed on very cold days.

  9. Chance says:

    Jacqueline Gauvin, you’ve simply been undersized. My home’s geo unit was installed in 1992, and though it has had a few issues, I’ve not had trouble getting anyone to look at it. I’ve also not had trouble with it keeping up with demand all the way down to -30f here in Michigan as well.

  10. Bill says:

    I have a 5 ton unit with water to water radiant floor heat. I used foam spray insulation with 2×6 walls. Works well only when it gets below zero will my heat pump lock out from high pressure. I usually reset it in morning and with zones still running water my house will stay warm till then. Once the heat of the day starts the heat pump can get the house back to 68. My house is 3,200 square feet with radiant in concrete floor in basement. My contractor mentioned that I may need back up heat when we installed geo system. He was sold on the foam spray insulation. I wish too that I could have a natural gas unit to supply heat in those rare cases. It costs way to install a boiler for those once in a great while incidents. Geo heat works best as radiant floor heat because of the lower water temperature in colder climates.

  11. Jason says:

    We have a water furnace geo thermal unit in our house . To let all know it will not keep house warm in winter when it gets cold! Very efficient and works great for cooling but until they come up with a natural gass back up stay away! We have a wood burning insert and also a natural gas infared floor heat we use! Also geothermal heat will take moisture out of air! We have to run a whole house humidifier that keeps humidity at a safe comfotable level! Thats my two cents worth cents! Dual fuel heat pump would be the way to go. I have had rep from water furnace at our house and they claimed everything was right with system! If it want heat your house and raise temp in your house it aint worth shit!

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