An article about geothermal greenhouses for the north

I’d love to have one of these.


They work best in Z4-5 climates where winters are cold and summers usually not too hot. Say KS, CO, SD and Iowa. Down here it would work very well in winter because air and soil aren’t too cold. But soil is too warm in summer to cool the greenhouse unless the underground system of pipes were huge.

I couldn’t get the chilling I do now using this system. Days would be too warm unless the greenhouse were heavily shaded in winter.

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A few of the cottages on Russell Island where my cottage is have the geothermal systems. They work well! Reading the article it seems the systems on the Island are lot more sophisticated providing air conditioning in the summer as well as heat in the winter. If I were to build such a beast, I would use the systems being used around here.

You’d have to dig pretty deep up here to catch heat from the ground.

These are current soil temps around Wisconsin. My guess is the differences are due to snow cover.

Talking with a guy who has a greenhouse near Milwaukee…the biggest issue is cloudiness…especially in Nov/Dec. We can go 20-25 days without sunshine in Dec. I have a small tunnel up and i was inside there this afternoon (teens F) and it must have been in the 70Fs or better, but it’s very sunny. It was below 0F last night.

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Very interesting! I live in Nebraska and didnt know this even existed. My brother brought up the idea of a underground green house last year, but he was talking about having the roof even with the ground. I said there was no way that system would provide enough light during the winter months to support growing plants then. However, with the 4’ depth on the south I see how you could elevate the plants enough to get adequate sunlight.

Fruitnut how much does disease and insect pressure decrease with a green house system? I am sure you have discussed it in your postings, I am just too lazy to go back through it all!

Warmwxrules I think they say the piping is buried at 8’ deep.

Disease is nearly non existent in my greenhouse. I keep the humidity as low as possible. The underground system is much more closed therefore humidity will be higher than mine. That may cause some issues. Compared to outside, I’m not sure. The only insect of real concern is spider mites.

I can tell you this my production inside is many fold outside on an area basis. There are no losses to wind, hail, freezes, birds, coon, etc etc. I grow many stone fruit inside that are hopeless outside, mainly due to spring freezes.

Yeah…it also helps that they are in Nebraska which has a more mild winter climate. Areas out there can heat into the 70Fs in Jan at any time of the winter. Around here a winter heat wave is usually mid 40Fs. I do believe there is a pit greenhouse in southern Minnesota over by Badgersett Farm…that uses no heat. Its possible even here, just need to go deep enough while still allowing in that low winter sunshine. My basement floor (concrete over soil) is around 56F to 57F right now…pretty typical for mid/late winter–no heat down. My well water runs in the low 50Fs most of the year…even in mid July.

If you want to see a good thread on pit greenhouses, check out what the banana guys do.
The guy in Kansas fruits bananas.

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FWIW- we have used a geothermal systm for our house for about 10 years now and it works well. As remarkable as it sounds, a properly designed system can extract heat from very cold ground. Remember, even at the freezing point of water it’s still 273 K above absolute zero. Our system is a Climatemaster Tranquility 27. We use water pumped from our well and drained into a dry well. No problems so far, but we do pump a lot of water in very cold weather.

Chena hot springs outside of Fairbanks Alaska has a greenhouse heated by geothermal. They also generate electrical power from it. They have been doing cutting edge work for 20 years. Here’s a bit of info from their web page.

Chena Hot Springs is working toward becoming a self-sustaining community, and an important part of making this vision a reality is to strive for greater independence in food production. Chena installed a small test greenhouse in 2004, which has operated year round and is heated entirely with water from our geothermal resource. One January, we were able to maintain the standard greenhouse temperature of 78°F while outside temperatures dropped to -56°F, which is typical for Interior Alaskan winters. This 134°F temperature differential was the largest recorded for any controlled environment production facility in the U.S.


Darn that must result in some serious ice on the greenhouse walls!!! I’d think you’d have to melt it off with a steam cleaner. Would also be a very humid structure.

There are several variations of earth tempered GH in practice today. Pit GHs do work, but from what I have seen of them and the people I spoke with about them, there is definitely some “tuning” to local conditions and what you are growing needed for them to work well. I do know some people who use them, but mostly for starting plants in the spring not as a year round thing on the plains of Colorado. They also can have issues with capturing enough sun for high light demand plants.

An interesting variant/hybrid is the SHCS GH (stands for: sub-terrain heating and cooling system, I think) design. It basically buries a grid of 4" flex drainage pipe in the subsoil of the GH and puts in a blower to push hot air thru those tubes. It cools the GH during the day, releases heat back at night and cold weather, and does so with minimal energy inputs (electricity to run the blower). It also tends to dehumidify the hot air. Unfortunately John C the inventor died a few years ago, and his website with spreadsheet calculator is no longer online. But the concept is a good one IMO. Using the soil as heat storage has 2 main benefits: First it does not take up room in the GH. Second warmer soil helps plants tolerate colder air temps. In my area, this along with some remay type covering inside is generally enough for winter growing of greens.

Although these designs have been built in many locations, I am familiar with the ones in Colorado. Here, a SCHS GH can expect to extend the growing season roughly a month on either end with no additional heat source. Smaller GHs with additional heat storage may be able to stay above freezing year round (my smaller GH does this most of the time, 13/15 years). The SHCS will not provide enough heat in the winter without supplemental heat for year round growing, nor will it do enough cooling in the summer without shade cloth and venting in our climate. But I have read reports of it doing these (but not usually both) in other climates.

IIRC there was a college in Virginia which built a SCHS GH and took some measurements on its performance.

Anyhow, I mention this as a possible design for those that want a low energy input GH.

I graduated from U of AK in Fairbanks in 83. We used to go to the hot springs several times a winter, but that was before he had the greenhouse. You’re right about the humidity, but I don’t recall any ice on the glass. The water coming out to the ground was about 120F if I recall right. The hot tub was 106 and the swimming pool was 95. They steamed like crazy. We would soak in the hot tub then go roll in the snow and jump back in. That was one hell of a body rush. It worked great with fresh snow but with 1 month old snow at -40F, it crystallized into ice shards. It was like rolling on 80 grit sand paper. I was more selective about the snow conditions after that!

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I did something similar for my greenhouse in Anchorage. I laid concrete blocks on their sides so the holes lined up, ran cable thru the holes and post tensioned the assembly. A fan on a t’stat sucks air from the peak and blows it thru the block. The beds are framed on top of the blocks. After 25 years of frost heaves, the blocks are still level, so it worked great. Warming up the soil is critical in a cold climate like Alaska.

I agree with you, the ground does not absorb enough heat, so an exhaust fan is still required. It will hit 120 in there on a 70 deg day without the fan.

I extended the system to the veggie garden as well. A fan sucks air out of the greenhouse and blows it thru 3/4 PVC tubing buried 6" in the raised beds. The other ends of the PVC vents to open air. That made a huge increase in the productivity of the garden. The carrots literally doubled in size.



That’s an interesting idea, to use the waste heat from the GH to warm outside garden soil. Unfortunately my GHs are too far from the garden beds to make that practical.

One thing I have been meaning to try is to increase the airflow thru the underground tubes. The original SHCS calculator cranked out a number for CFM of the blower, and that’s what I put in. But there has been some discussion that those CFM numbers were pretty low, and 2-3x what they called for would help move substantially more heat into the ground. I typically see a 10-15F temp drop now, so if I could increase that it would help in several ways. Still likely need additional cooling help in the summers here.

Seems like there is quite a bit of low or minimal tech GH temp control techniques, and more that we could learn. Perhaps it will get more popular again with more folks experimenting and finding new solutions.

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That is exactly how i use my tunnels. Up here Oct-Feb are worthless for plant growth (not enough sun/days too short). By late Feb you can start to see plants move. I know Eliot Coleman in his book just shuts down for a couple months in the winter. I honestly wouldn’t waste my money trying to heat a greenhouse in the winter months. To me the money would be much rather spent buying some grow lights and use the basement/porch/etc to overwinter tender plants. At least in that case the waste heat from those fixtures can go towards heating the house.

I’d have to dig it up, but i believe i read about a family out in Idaho using geothermal water to heat a greenhouse (for tomatoes).

A guy near me i know put in a geothermal system maybe 15 years ago. His has one big loop down that is at least partly submerged in 50F ish well water. I don’t think he’s too impressed with the heating, but i wonder if his isn’t an optimal setup (not enough surface area for heat transfer) with such little amount of pipe he has in the ground (he didn’t have the area for a large field of poly pipe). I do know that his AC works very well. Not sure the COP of those systems, but they must be near 3 or better. The cost of his was considerable and he did it before there were and large rebates (my memory seems to thin it was $25K ish).

My interest the past few years have been mini split heat pumps. The newest units are pretty amazing. I just became aware of one system (below) that works down to -22F (although at that temp you got to wonder what sort of COP your going to get @17F the COP of 3…) so if you put in 1500 watts, you get out 4500 watts of heat. These units also do a great job with AC. Out east i know they build very efficient new homes and the only heat source is a mini split system. I may install one here (not sure what model). What i would do is only run it when temps are say 5F or above since the efficiency on them seems to be that much higher when the temps are more moderate. I’ll have a wood stove for temps below that.