Older house with geothermal

[Alaska_Skeeter]

We are moving and downsizing.
Some homes on the market have geothermal heating/cooling (Montana),
and they are typically older than 25 years.
What type of major issues may be of concern in older geothermal systems?
Or is most of the high cost up-front in installation and issues relatively minor in terms of potential repairs?

[desiderium]

A significant chunk of the up front cost is the underground pipe. That part shouldn't be such a concern. If the heat pump unit is older, you could consider having someone who installs and repairs these units to inspect for you; the seller is obliged to supply a functioning heating system. Replacing the heat pump unit is not going to be cheap, and if you buy an older one you should factor in the replacement cost at some not too distant time. Geothermal is a big advantage overall, so it will still be worthwhile compared to other technologies.

[Valuethinker]

We are moving and downsizing.
Some homes on the market have geothermal heating/cooling (Montana),
and they are typically older than 25 years.
What type of major issues may be of concern in older geothermal systems?
Or is most of the high cost up-front in installation and issues relatively minor in terms of potential repairs?

A relative had one on their farm in Ontario, Canada. (So similar climate but less extreme temperatures mostly than yours). They installed in the early-mid 1990s (there was a utility subsidy at that time). Sub surface but not vertical bore (I think trenches about 2-3' down).

There was a problem that the routine maintenance (this was after 7? or 10? years) used the wrong fluid (citric acid?). Their water was very hard & so scaling of the pipes was an issue. That damaged the thing and the unit needed replacement.

Other than that in 25 years of ownership they reported no problem. They were disappointed when they moved into a condo in town and had to switch to natural gas (their unit had its own furnace).

Given the age, you probably will have to replace the unit within 5 years. It's something to budget for.

Air Source Heat Pumps have improved heating efficiency by leaps and bounds - getting close to geothermal levels. I don't know if geothermal HPs have also improved technologically - but I would imagine they have (better Coefficient of Performance) even if not to the same extent. Certainly with the Russia/ natural gas supply crisis in Europe, HP installations (both types) are growing by leaps and bounds.

I imagine, given this is Montana, that the backup heating system is wood? Presumably your electric power does go out - when there are bad winter storms. And it can take many hours (or days?) for it to get restored?

[ralph124cf]

I believe that it is incorrect to call ground source heat pumps "Geothermal", although I know that it is common.

I believe that geothermal heating terminology should be reserved for naturally occurring hot springs, or hot water that can be reached by drilling a few hundred or a few thousand feet deep. This type of "Geothermal" does not need any type of heat pump, the hot water is simply pumped to wherever heat is needed. The entire city of Reykjavik in Iceland is heated this way. My understanding is that the lodge in Yellowstone National Park is also heated like this. Note: The hot water available a few hundred to a few thousand feet down is not suitable for direct use. It is usually a few hundred degrees, very acidic, and with a high sulpher content. Like a ground source heat pump, a loop has to be driven, and water is then circulated to transfer the heat up to where it can be used by transfer to a hot water supply.

[snic]

I believe that it is incorrect to call ground source heat pumps "Geothermal", although I know that it is common.

I believe that geothermal heating terminology should be reserved for naturally occurring hot springs, or hot water that can be reached by drilling a few hundred or a few thousand feet deep. This type of "Geothermal" does not need any type of heat pump, the hot water is simply pumped to wherever heat is needed. The entire city of Reykjavik in Iceland is heated this way. My understanding is that the lodge in Yellowstone National Park is also heated like this. Note: The hot water available a few hundred to a few thousand feet down is not suitable for direct use. It is usually a few hundred degrees, very acidic, and with a high sulpher content. Like a ground source heat pump, a loop has to be driven, and water is then circulated to transfer the heat up to where it can be used by transfer to a hot water supply.

I agree, it's confusing. Got to come up with a less clunky term than "ground-source heat pump", though.

(Stayed in a vacation rental house in Iceland in which hot spring water came out of the hot water tap, smelling like the devil and just about as hot as his residence. To take a shower you had to turn the cold water on first, then add a tiny bit of hot water to the stream, or you risked scalding yourself. Not sure how far down they drilled to get the water, but I'm guessing not too far. There are hot springs everywhere in Iceland.)

[TomatoTomahto]

I believe that it is incorrect to call ground source heat pumps "Geothermal", although I know that it is common.

I believe that geothermal heating terminology should be reserved for naturally occurring hot springs, or hot water that can be reached by drilling a few hundred or a few thousand feet deep. This type of "Geothermal" does not need any type of heat pump, the hot water is simply pumped to wherever heat is needed. The entire city of Reykjavik in Iceland is heated this way. My understanding is that the lodge in Yellowstone National Park is also heated like this. Note: The hot water available a few hundred to a few thousand feet down is not suitable for direct use. It is usually a few hundred degrees, very acidic, and with a high sulpher content. Like a ground source heat pump, a loop has to be driven, and water is then circulated to transfer the heat up to where it can be used by transfer to a hot water supply.

I agree, but in real life, people refer to it as geothermal. You want a house with GSHP on Zillow? Type geothermal into the search criteria.

Having 5 year old GSHPs at my house (vertical wells in Massachusetts), I’m following this thread with interest. Fwiw, the first 5 years have been wonderful, here’s hoping for another 20+.

[Alaska_Skeeter]

Do most ground-source-heat pumps use 100 percent glycol?
If so, then mineral deposits would not be an issue, but how would domestic hot water be heated?

If water is used, would not the system eventually become clogged due to mineral deposits?

Is the heat pump technology specialized such that it might be difficult to find an expert to inspect
and/or repair? The closest city over 25,000 people is 80 miles away.

Thanks for all the replies!

[Cruise]

I believe that it is incorrect to call ground source heat pumps "Geothermal", although I know that it is common.

I believe that geothermal heating terminology should be reserved for naturally occurring hot springs, or hot water that can be reached by drilling a few hundred or a few thousand feet deep. This type of "Geothermal" does not need any type of heat pump, the hot water is simply pumped to wherever heat is needed. The entire city of Reykjavik in Iceland is heated this way. My understanding is that the lodge in Yellowstone National Park is also heated like this. Note: The hot water available a few hundred to a few thousand feet down is not suitable for direct use. It is usually a few hundred degrees, very acidic, and with a high sulpher content. Like a ground source heat pump, a loop has to be driven, and water is then circulated to transfer the heat up to where it can be used by transfer to a hot water supply.

Thanks for clarifying the OP’s situation. I’m familiar withe the Icelandic system, and wondered whethe I missed something about the geology of Montana.

[Valuethinker]

I believe that it is incorrect to call ground source heat pumps "Geothermal", although I know that it is common.

I believe that geothermal heating terminology should be reserved for naturally occurring hot springs, or hot water that can be reached by drilling a few hundred or a few thousand feet deep. This type of "Geothermal" does not need any type of heat pump, the hot water is simply pumped to wherever heat is needed. The entire city of Reykjavik in Iceland is heated this way. My understanding is that the lodge in Yellowstone National Park is also heated like this. Note: The hot water available a few hundred to a few thousand feet down is not suitable for direct use. It is usually a few hundred degrees, very acidic, and with a high sulpher content. Like a ground source heat pump, a loop has to be driven, and water is then circulated to transfer the heat up to where it can be used by transfer to a hot water supply.

It was a marketing thing. "Heat Pump" in American-ese means Air Source Heat Pump. Ground Source HP was felt to be too technical.

I don't know about other languages (Sweden & the Germanic countries HPs are a very popular technology) but outside USA in the Anglosphere, I think Ground Source Heat Pump still predominates (not sure about Canada, to be fair).

You are pushing water uphill on this one. The common parlance is what it is. We don't say Thou or Thee any more either .

[Valuethinker]

Do most ground-source-heat pumps use 100 percent glycol?
If so, then mineral deposits would not be an issue, but how would domestic hot water be heated?

A heat exchanger-- that's how most European systems work ("indirect system" - the furnace is a "boiler" which provides hot water & hot water for the rads, on separate circuits). Or a separate HW system w its own heater (electric induction typically, could be propane or even wood)-- that's more the North American practice.

If water is used, would not the system eventually become clogged due to mineral deposits?

An open circuit system using water is relatively rare, I believe. For precisely this reason. But it can be cleaned.

Is the heat pump technology specialized such that it might be difficult to find an expert to inspect
and/or repair? The closest city over 25,000 people is 80 miles away.

Thanks for all the replies!

Repair would be an issue. But the local installer is also often the supplier of repair & maintenance.

After all, for *any* system, the closest city over 25k is 80 miles away. So propane or wood systems also break down.

[Valuethinker]

I should note poster talzara seems to know an enormous amount about heat pumps.

Mostly our discussions are about Air Source HPs. But if you do a search on their posts.

[TomatoTomahto]

Do most ground-source-heat pumps use 100 percent glycol?
If so, then mineral deposits would not be an issue, but how would domestic hot water be heated?

If water is used, would not the system eventually become clogged due to mineral deposits?

Is the heat pump technology specialized such that it might be difficult to find an expert to inspect
and/or repair? The closest city over 25,000 people is 80 miles away.

Thanks for all the replies!

I believe that my system uses “food grade” glycol mixed with water. Domestic hot water is heated separately in my system, but some systems provide domestic water preheated by the heat pump as input to a water heater for winter use (see desuperheater).

We have sufficient geothermal techs around us, and our installer is a thriving business, but I can’t speak to Montana. The technology has progressed recently, with variable speed pumps and smart thermostats, but the basic technology of heat pumps has been around for a while. We chose a high end WaterFurnace installation for our home with 4 zones in 3 units.

[Valuethinker]

I believe that it is incorrect to call ground source heat pumps "Geothermal", although I know that it is common.

I believe that geothermal heating terminology should be reserved for naturally occurring hot springs, or hot water that can be reached by drilling a few hundred or a few thousand feet deep. This type of "Geothermal" does not need any type of heat pump, the hot water is simply pumped to wherever heat is needed. The entire city of Reykjavik in Iceland is heated this way. My understanding is that the lodge in Yellowstone National Park is also heated like this. Note: The hot water available a few hundred to a few thousand feet down is not suitable for direct use. It is usually a few hundred degrees, very acidic, and with a high sulpher content. Like a ground source heat pump, a loop has to be driven, and water is then circulated to transfer the heat up to where it can be used by transfer to a hot water supply.

Thanks for clarifying the OP’s situation. I’m familiar withe the Icelandic system, and wondered whethe I missed something about the geology of Montana.

10-15 years ago the industry agreed to move to "geothermal" as a descriptor. At least in North America.

GSHPs are a thing in Canada since the energy crisis of the 1970s. There was a Federal subsidy for them, I think, in the early 1990s. It is not a new technology (been around in Scandinavia since the 1960s I believe).

[chazas]

I had a home with a ground source heat pump. There was a leak in the loop. It was cheaper to keep refilling it than try to find and repair.

[Valuethinker]

I had a home with a ground source heat pump. There was a leak in the loop. It was cheaper to keep refilling it than try to find and repair.

I am guessing it had water in the loop?

Otherwise leaking a contaminant could be a major league nightmare: both on resale of the home and on groundwater contamination (which could lead to lawsuits by your neighbors).

[TravellingTechOnFire]

Do most ground-source-heat pumps use 100 percent glycol?
If so, then mineral deposits would not be an issue, but how would domestic hot water be heated?

If water is used, would not the system eventually become clogged due to mineral deposits?

Is the heat pump technology specialized such that it might be difficult to find an expert to inspect
and/or repair? The closest city over 25,000 people is 80 miles away.

Thanks for all the replies!

Distilled water eliminates mineral deposit issues, and some anti-freeze for insurance against freezing. You'll need to know how deep the lines are. If they are quite deep for your area, less anti-freeze will be needed. The less the better in terms of heat transfer AFAIK. If the lines are a bit on the shallow side, making them more susceptible to freezing in a cold snap, you'll want more freeze protection i.e. more anti-freeze.

[andypanda]

You know what they say about fighting city hall:

www.energy.gov/energysaver/geothermal-h ... emperature.

"Geothermal heat pumps (GHPs), sometimes referred to as GeoExchange, earth-coupled, ground-source, or water-source heat pumps, have been in use since the late 1940s. They use the relatively constant temperature of the earth as the exchange medium instead of the outside air temperature. "

[TomatoTomahto]

We are moving and downsizing.
Some homes on the market have geothermal heating/cooling (Montana),
and they are typically older than 25 years.
What type of major issues may be of concern in older geothermal systems?
Or is most of the high cost up-front in installation and issues relatively minor in terms of potential repairs?

You are lucky to be seeing many geothermal listings. I won’t buy another house that doesn’t have geothermal or an easy enough retrofit. We installed ours 5 years ago and it’s a delight.

[London]

When I purchased my house in 2015, there was a barely functioning geothermal system with loop issues. In addition, the inside units were aging. While I like the technology, we replaced with traditional furnace/AC units. Going forward, they will cost more to run but much less to repair.

[Valuethinker]

When I purchased my house in 2015, there was a barely functioning geothermal system with loop issues. In addition, the inside units were aging. While I like the technology, we replaced with traditional furnace/AC units. Going forward, they will cost more to run but much less to repair.

And Air Source Heat Pumps are much closer in performance to GSHPs than they once were.

OP is buying in Montana in a rural area, so:

- ASHP may just not cope with the climate extremes
- propane and/ or wood are probably the furnace options? (I am guessing no one out there uses heating oil, which itself has a minimum temperature?)

[chazas]

I had a home with a ground source heat pump. There was a leak in the loop. It was cheaper to keep refilling it than try to find and repair.

I am guessing it had water in the loop?

Otherwise leaking a contaminant could be a major league nightmare: both on resale of the home and on groundwater contamination (which could lead to lawsuits by your neighbors).

I had no idea. Sold it - it took a couple years to sell, but for other reasons.