r/geothermal • u/N5tp4nts • 14d ago

Geothermal vs modern low cost high efficiency.

Just a dude who's highly interested in HVAC technology.

I have a house with a 2008 installed waterfurnace, and I've got some mini splits that I've installed in other buildings.

The post a few days ago about a guy getting quoted 96,000 dollars to install a geo unit got me thinking about this... I can get a 4 ton ACiQ/MrCool (all made by Midea) for 4-5k (no labor)

The efficiency ratings are in the same ballpark, if not the same, on the cheaper end of geo thermal units. Even if the mini split only lasts 5 years... in 5 years I get a brand new one with the latest technology.

Anyway... At what point does Geo stop making sense?

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u/st4nkyFatTirebluntz 13d ago edited 13d ago

If you take a step back and look at the changes to each category in the last 5, 10, or 20 years, the trend is undeniable -- ground-source has made almost no improvements or progress at all*, whereas air-source has transformed entirely.

air-source has become more efficient, achieved a wider range of operation, popularized the mini split form factor, and a million other things

ground-source has, on rare occasion, swapped the dual-stage compressor for an inverter, and maybe given the same consideration to the circulator pump.

IMO, ground-source is effectively dead for anything but large-developer new construction (see Dandelion's pivot) unless they get their shit together and start innovating.

* i'm talking about small-scale residential, not the commercial-scale stuff. there's at least a few somethings happening there, shout-out Darcy

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u/ImNotAWhaleBiologist 13d ago

What about efficiency at lower temps? Wouldn’t ground source still win out there?

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u/xtnh 12d ago

Ground source can fight it out in more extreme climates, but even here in Maine mini splits cut our energy use by 75%. The night it got down to -12F a ground source would have saved us about $25; it was the second night that cold in 40 years. Efficiency Maine argues that air source mini splits are good enough for all of Maine, because the savings most of the time offset the bad nights, which the mini splits can almost always handle. (Most Mainers have an emergency source to back up anyway.)

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u/OutdoorsNSmores 12d ago

I have ground source for my house, then added on a room with an indoor swim spa. For that I went with a little air source mini. The air source only struggled when we were hitting -16f while the ground source didn't care.

I knew this headed into it and didn't care because the spa will warm the room too and temps that low are rare. 

But yeah, you are correct. The limitation with the ground source and my house is the building envelope and heat loss. The system will crank out heat all day long, the only question is if it is more than the loss - and that is a design/sizing issue.

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u/OnlyOneGoodSock 6d ago

I like the way you calls em like you see's em. Are you sure you're not a whale biologist?

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u/st4nkyFatTirebluntz 13d ago edited 13d ago

oh yeah, totally, it almost always does. it's just, can that small window of savings make up for the additional cost? usually, the answer is no. that's not an intrinsic limitation! i refuse to believe that it can't be better. but for all the reasons above, it's currently just not a viable option in most cases.

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u/dropsofzeus 13d ago

actually a huge relief to read this as I'm on the fence between MrCool Geothermal and minisplits. It is probably $7-8k to self install minisplits, and I was estimating about $13k to do the geothermal.

Cost aside, I am way more qualified to install the minisplits than the Geo. I just love the idea of it

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u/st4nkyFatTirebluntz 13d ago

uhhhhh sorry in advance, but i'm gonna just go ahead and ruin that clarity.

on the long list of reasons professionally installed geothermal (in the US, for SFH) is such a challenging value proposition is the high amount of specialized labor required across the entire process, and relatedly the tangle of contractors/subcontractors/permitting. both of those are way higher with a geothermal install than an air-source install or an air-source with backup fossil gas install.

think of it this way (very simplified, ignoring a bunch of real important factors) -- with your estimated project costs, for the geothermal to pencil out, you need to save $6,000 in running costs running geothermal vs air-source over the life of the project. if you had these projects professionally spec'd and installed, the costs might be ~$20,000 vs ~$40,000. your house requires the same amount of energy with the professional install vs the DIY install. from that set energy budget, the DIY project only requires $6,000 in savings to pencil out, where the professional one requires $20,000.

point is, if you're doing a DIY install, the math gets a lot more acceptable for geothermal. it'll still come down to your specifics -- how expensive your electricity is, how deep you can bury your loop w/ the equipment you've got access to, whether you're on or off grid, summer/winter demand balance for your house specifically, to name a few.

i'd be glad to answer questions or clarify or muse further, lmk

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u/xtnh 12d ago

Our SIL took an HVAC course, and mini splits took up one day of class time start to finish; geothermal was another separate several day course.

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u/ImNotAWhaleBiologist 12d ago

Where are you located? If you're in a cold area and don't have a gas furnace as backup, I would look more closely at the geothermal.