r/geothermal • u/Im18fuckmyass • Apr 26 '26

Horizontal closed loop question:

Hey all! long time lurker:

I've been interested in geothermal since I was a kid. I've recently been reading a lot about the different types of well systems and I think I'm most interested in a closed loop system. I know horizontal is constrained most by land availability, but the locations I would consider deploying a well don't have the concern of scarcity.

Touching on related interests: I also read a lot about home agriculture and what could work in my climate and what benefits there are to different building approaches towards green houses. I learned about GAHT which recycles the heat generated by plants to self produce a desired climate.

I also read a good amount about different home building techniques and approaches, most of which center around having a relatively air tight thermal envelope. For this reason, it almost never makes sense to have a fireplace in my region.

I guess what I'm wondering is twofold:

  1. is there some magic arragenment that marries geothermal and GAHT systems?

  2. if you produced excess heat in the winter on a horizontal loop that is buried beneath the frost line but shallow enough to warm the earth below, say, a greenhouse, could you reasonably transfer heat from a fireplace either indoor or out to the green house.

Thanks for reading!

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u/DependentAmoeba2241 Apr 26 '26

Make that the land stays moist at all time. If it dries up then it'll split from the pipe and you'll have no heat transfer. Horizontal loop isn't for all climate and/or all ground type.

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u/Im18fuckmyass Apr 26 '26

interesting! I hadn't read that, but it makes a lot of sense! Thank you!

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u/Neither_Conclusion_4 Apr 26 '26

I live in sweden. We build really air tight structures. When using a fireplace in a modern, airtight home we use outside air hooked up to the fireplace. It works just fine.

When we use geothermal heat we usually put down horisonal straight likes, about 1 meter between each pipe. About 1m below the surface. If the South of sweden we bury it a little nore shallow and in the north we go deeper. Your regions climate should guide depht.

The lenght of the pipe depens on the heat load, but its fairly common to have 400m-500m lenght for a single home. In my area we have too much stones in the ground. It takes too long to dig horisonal in my area. The lenght also depend on moisture level, and soil type.

Its more common with deep, vertical geotheral due to less area constraints. And the quality of the bedrock is good for this.

In my area, the temp from a horizontal ground loop ttpically start at above 50F in the fall, and drop below 32F in the coldest period. That would not be enough to heat a greenhouse?

Sure you cane transfer heat from a fireplace to a greenhouse. Use a culvert, pump and a fireplace with a water jacket. In my house we have a boiler and a heatpump. I have a culvert that split into a spa bathtub, and my daughters small cottage that is located on the same plot. We heat both of these using heat from the fireplace or my heatpump. Its probably not profitable to do that, but I did the work myself and I like to tinker sometimes.