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What I want to know is a simple setup that can heat/cool a house using hdpe or pex pipes coiled deep underground (depth of approx 13 feet or 3.9 metres) through which air is circulated and thus, utilising the constant temperature of the soil that is maintained throughout the year - which is around 22°C or 71.6°F

I have a handpump in the lawn and noticed that the water from it feels really cool to touch in summers and really warm in the winters. (The max weather temperature here in summers reach around 38°C or 100.4°F and as for winters, the minimum reaches about -10°C or 14°F).

Also, the water table is quite high in my area (approx 1.5 metre or 4.9 feet) which seems to be helpful in further maintaining the constant underground temperature throughout the year.

  1. Can the following simple set up do the job of maintaining the temperature of the house? -- a pipe (approx 8 inches/20 cm in diameter) is laid underground and air is circulated through it using exhaust fan into the house... would it be possible to maintain the temperature inside the house to some extent? Of course a single pipe would be going into the ground, but the pipe that comes out would then be insulated and then further branched out to different parts of the house.

  2. Also, if the soil is modified - as in - the bottom most layer (where the pipes are laid) would be sandy soil, and the layer in the middle is a mix of silt & loam, and the topmost layer is clayey+loamy soil (4 feet each layer)... would that further help in this set up?

  3. Also, what about the humdity/condensation? Would that cause any mold formation inside the pipes? How to prevent it?

Thanks a lot in advance for any insight/advice. I would very much prefer it to keep this setup as simple as possible.

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  • $\begingroup$ I had a vendor come to my house years ago to try to sell me a "geothermal" system some what akin to what you describe. They were going to cycle ground water through a heat exchanger with a heat pump. In my area, it would require digging a DEEP hole through rocky soil which made it cost prohibitive. The idea of using 10C water for heating and cooling all year long was good, if the ground water was not so far down, I might have it now. $\endgroup$
    – user1683793
    Commented Nov 28 at 0:59
  • $\begingroup$ @user1683793 used in many places, just need to check the details. $\endgroup$
    – Solar Mike
    Commented Nov 28 at 5:38

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A technique used for many years.

Search for "puit canadienne" - at least that was where I started when I was designing the one we put in in Switzerland.

put 30m of pipe (3 tubes 25cm diameter of 10m in parallel) 3m below the ground surface. the temperature range at that depth is 5 to 8 deg C, which provides free heat in winter when the outside air temperature is below zero and down to -14 deg C and cool air in summer when temperatures can exceed 30 deg C.

You need to design the diameter and length to match the volume flow rate so the air delivered to the house has had sufficient time to heat or cool.

Also you need to consider a slope so any moisture can get out of the pipe system.

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  • $\begingroup$ That is really helpful! Thanks a lot. Just a little clarification on your last point --- "Also you need to consider a slope so any moisture can get out of the pipe system." ---- The water table here is approx 1.5 m... and if I bury the pipes upto 3 m depth ... how to get the condensation to flow out with a slope? $\endgroup$
    – Little Shade
    Commented Nov 28 at 14:51
  • $\begingroup$ Don't go below the water table, or get the pipe joints plastic welded if the water temperature is suitable. $\endgroup$
    – Solar Mike
    Commented Nov 28 at 14:59

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