GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Audio Play Icon Headphones Icon Plus Icon Minus Icon Check Icon Print Icon Picture icon Single Arrow Icon Double Arrow Icon Hamburger Icon TV Icon Close Icon Sorted Hamburger/Search Icon

Community and Q&A

Geothermal house air supply

Dennis Vogt | Posted in Energy Efficiency and Durability on

I am trying to re-route my household fresh air intake to run under the ground and enter near the basement floor in order to warm it up in the winter and cool it down in the summer. I live in Wisconsin. I presently bring fresh air into the house constantly and route it to my furnace cold air return. For underground routing, I am concerned about radon gas and water getting into the tubing. I am also concerned about contamination of the air from the tubing.
Thank you,
Dennis Vogt

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. User avatar GBA Editor
    Martin Holladay | | #1

    Your concerns are appropriate. Buried earth tubes have so many disadvantages that they are rarely installed these days -- and with good reason. Here is more information: Belgian Passivhaus is Rendered Uninhabitable by Bad Indoor Air.

  2. Dennis Vogt | | #2

    Thank you Martin,
    I read the article and see at least in part how that system failed.
    I was considering running a pair of 4" diameter CPVC pipes (rated for potable water and covered with a screened rain cap) vertically downward until 6 feet deep and then running them horizontally for 15 feet except pitching them downward and then taking a 90 degree turn into the basement wall a foot above the basement floor. The CPVC joints would be glued. I was going to add a drain fitting inside the basement to drain any condensation from the summer. I was also planning on dumping some bleach/water mixture down the pipes from outside once a year to make it uninhabitable for mold. This design is affordable. Still, I share your health concerns. Assuming that water/mold is prevented, I am not sure about the CPVC being safe for the air.
    Dennis Vogt

  3. Jesse Smith | | #3

    You could run a coil through the ground and use it to pre-heat the air before it enters the return duct. Probably a little less risky, but more complicated. It might be cheaper for you to just install an HRV. Does the current system make you uncomfortable? Is the ventilation rate correct for the house? Most of the houses I see have ventilation rates set way to high...

  4. Dennis Vogt | | #4

    Thank you for the idea Jesse,
    I now see what you mean; circulate some fluid from the air intake vent to the ground. The incoming air would warm up from contacting the coil. Actually, the only thing that I don't like about it is that I need to use energy to run the pump.
    Dennis Vogt

  5. Dennis Vogt | | #5

    I measured the incoming air rate to be 75CFM, which is what I think is appropriate. The present system is working out fine. I am just trying to reduce the energy use.
    Dennis Vogt

  6. Sal Lombardo | | #6

    I was considering an "earth tube" or a version thereof as well Dennis. From what I've found websearching the issue, its not such a good idea after all. From what Jesse suggests, it sounds like a form of geothermal? I am not that knowledgable on such systems, but an underground coil that is used to heat or cool air sounds like a form of geothermal, no? If you look into it and find anything worth while let me know. At a minimum sounds like you'd be running a pump and a fan.

  7. Jan Juran | | #7

    Hi Dennis: UltimateAir makes an accesory, a 12" Water to Air Coil Module, which connects to its RecoupAerator 200DX ERV. The module can connect to a ground loop water/fluid pipe, to pre-heat and defrost in winter and to pre-cool and dehumidify in summer, the incoming air to their ERV. Check it out at: For example, 55F inlet water can pre-heat 0F outdoor incoming air to 31F into the ERV, mitigating the ERV's need to go into defrost mode. Similarly, 50F inlet water can pre-cool 95F incoming air to the 67F-72F range into the ERV (see tables pp. 5 and 6 in the link above). The Water to Air Module provides for condensate drainage. Energy savings should be weighed against the energy used by the water/fluid pump (2.5 or 5 GPM is typical) and the installation cost of the ground loop.

  8. JP Jon Pierce | | #8


    In 1995 at a county airport, 3200 ft vertical boring with 3/4 U-Paired tubing delivered not less than 7 useable TOTAL cooling tons and 4% DEHUMIDIFICATION exchanging 80-deg office air with 52 degree boreholes x 240 ft depths + headers in 5ft trenches combined, borehole static water was ~ 40ft deep in a standard grouted GEOTHERMAL 98% RENEWABLE installation. the 1.1/2hp circulator was quite less costly allowing a barely comfortable work area during construction.

    Interfacing thermal energy transfer from the Earth-Tube-Coupled-Ground-Loop-Exchanger (ECL, GLE, GTX, GL) cooled with common fancoils for chilled and HW for 23 tons heating and a little more than 17 net cooling tons (designed for 45fW x 76Air x 64rH x expected 40-44 GPM, were on site).

    TODAY: designs implementing decent energy savings at ground loops are 'well' under 22 ft TDH wtr INCLUDING the HtPump coil in the box, allowing for 1 pumping hp to work with nearly 26 "AHRI-RATED-'tons' (hah)" ~ 22+ Compressor-Tons for here to compare to ... or just getting near better-usable DIRECT GEOTHERMAL COOLING on that direct Earth-Tube-Fluid-Cooling with up to 1" sdr-11 (NOT sdr-9) ~ TWO (2) x 245ft bores per DIRECT -net-TOTAL-Cooling-Ton for through each fancoil face of about 2.1/2 sq ft fintube x 3row x ~ 500 CFM. insulated runs and cabinets and sealed ducting to SOLAR and Heat-Pump premium standards is essential. [Higher 7-9 GPM per net cooling ton is fine with WILO super variable pumps or things like 33gpm pumps that use under 500w at 25 ft TDH wtr. Swimming pool circulators by PentAir-Sta-Rite, etc, have fantastic res and comm equipment that is even better.

  9. JP Jon Pierce | | #9

    Please note any standard water in piping : Headers are for purging on occaision if your loops and headers are normally operating under 2.2ft per sec where almost all micro 'cling-ons' air bubbles clinging to smooth plastics, etc, are found that need then to be moved out of the piping at over 2.1-2.2 fps. Some 1/2" exchangers of piping coils have required over 2.2 fps.

  10. User avatar GBA Editor
    Martin Holladay | | #10

    You are the king of abbreviations.

    "ECL, GLE, GTX, GL ... HW for ... rH ...GPM ... ft TDH wtr ... AHRI ... hah ... sdr-11 ... WILO ... ft TDH wtr .... res and comm ... fps."


    (WOW is an abbreviation. It stands for "what obscure writing."

  11. User avatar
    Dana Dorsett | | #11

    If you only use phones for text rather than voice, ur styl gts prty trse. (Is it just a coincidence that "Twitter" begins with "twit"?? :-) )

    Writing for comprehension requires at least some filling in the blanks, otherwise great responses can become mere notes to ones self (GUILTY, yer honor!)

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |