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Comment by starkd | Hacker News Reader

Only a few feet deep? Maybe in select areas, but you generally have to go a lot deeper than that. It's been my understanding that the steep cost of geothermal involves the drilling. As much as $80K just to install a decent system, from what I've heard.

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A lot of it depends on how you design the system.

Using the ground as a heat source requires a relatively large installation as you need to make it big enough to draw heat from a large area, even as you use it year after year.

However, you can also use the ground as heat storage, and pump back heat during the summer. This greatly reduces the size, as you are not at risk of "exhausting" it.

Some geothermal systems use deep wells, others use coils of pipe buried a few feet down, below the frost line. If you're lucky enough to have a deep pond or lake nearby, you can put the coils of pipe in that.

In my understanding, it takes more to maintain such setups. Talking to the HVAC guys that do this for a living rather than just the scientists reveal more about the practical realities of these systems.

if you have land a horizontal trench at 7 ft will work just fine. I was going to do this on a new build but building code basically required a heat pump to start with. I was going to put in a cheap furnace for the first year or two and install a ground source heat pump myself, but with the cost of my regular heat pump it will never make sense to change over.

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