Inexpensive Home Building

Cut through the jargon and nonsense of home building and house construction by starting from zero dollars and trying to figure best-value bang-for-your-buck when choosing construction methods or construction materials. My research might answer some of your questions and at other times perhaps you have the knowledge or experience to post the answers to my questions and thereby help others too. The goal is an affordable and sustainable home for all.

Wednesday, December 13, 2006

The Myth of Geothermal Heating Efficiency?

Geothermal heat taps the Earth's heat "for free." An example of a passive system is a vertical tube driven below the frost line so the constant non-freezing temperature beneath most populated areas rises through the tube--simple to keep cattle's outside water trough from freezing. However, the typical home would use an active system:
  1. Boosting the ballpark 50-ish-degree* earth temperature to typical room temperature and hot-shower temperature requires heat pumps/compressors to add heat--so you still need some type of "furnace" *(Edit: I had already mentioned the hotspot variance but here's more detail: Geothermal temperatures vary from hotspot hot springs like Yosemite park to permafrost like Alaskan tundra--and the contiguous 48 U.S. states vary in broad bands of 37-77 degrees F from north to south; it is better if your area has "room temperature" geothermal heat but unfortunately the lowest heats generally are in the north where you need heat most).
  2. A typical home needs a vast underground radiator of tubes to "mine" the Earth's heat. This outdoor system is an additional up-front capital cost not needed by conventional heating systems (compare the vertical loop to well-digging and the horizontal loop to septic/sewer excavation to get some idea of cost).
  3. A typical home still needs some type of indoor HVAC system to circulate the geothermal heat.
One showcase geothermal-heated home includes the waste heat from electrical machinery in its "geothermal" performance rating--so much of the reported "geothermal" heat is actually electric heat. The extracted geothermal heat in mid-latitude USA (Mc Henry MD) measured 49.6 degrees F and provided 17,250 BTUH. However, all the electrical pumps required for this geothermal system create an electrical load of up to 3,502 watts, equivalent to 11,952 BTUH of electric heat. In other words, if you could run all the geothermal system's electrical equipment under load in the middle of your living room but not connected to any geothermal heat source, you would generate electromechanical heat equal to about 70% of the potential geothermal heat--without the cost of excavation and underground equipment.

I read somewhere that a syndicated home energy show designed an HVAC system with:
  • a Marathon water heater
  • a geothermal heat system
  • a heat exchanger so that the geothermal heat pump's heat would provide supplementary heat to the hot water
The owners enjoyed all the hot water they wanted for over a year before they accidentally discovered that they had forgotten to turn on the Marathon hot water heater--the entire household's hot water needs were met by the electric heat or waste heat of the heat pump for the geothermal system. That's a lot of expensive electric heat masquerading as a "free" "geothermal" heat system.

Rough comparative indicators of heating system efficiency suggest that geothermal costs 50% less than conventional annual HVAC to operate but geothermal costs 50-100% more to install. If you don't pay an extra $10,000 for geothermal installation in new construction and instead put the cash in a 5% money market account, the interest will pay $500 per year (before taxes). The $20,000- $30,000 cost of geothermal-converting an existing home instead put into a 5% Money Market would pay $1,000-$1,500 of your conventional HVAC--and you'll still have the principal cash as an emergency fund (your doctor or car mechanic might not accept geothermal tubes as payment). If you lack cash, borrowing the higher installation cost makes geothermal even less of a bargain. The government might subsidize a geothermal home system but government subsidy could be yet another telltale sign of active geothermal's inherent inefficiency.

Even though commercial geothermal systems might reach their break-even point after a decade or two (when net operating savings finally exceed the initial premium in constant dollars), I fear that the good geothermal idea fell victim to conventional, expensive thinking but with superficial appeal to gear heads, penny pinchers, and tree huggers (the new Green "Glam").

This article's title is a question, not an answer, but those are my concerns. I would like to see comparative data with a passive geothermal tube design, and also an earth-sheltered design without external tubing (with only the Earth against the walls as the passive geothermal heating system). Given a walkout-basement-style earth-sheltered design, what is the most cost-efficient heating system (initial and operating costs including risk of broken equipment) to maintain 65 degrees for room temperature?


At 3:08 PM, Anonymous Don Stephens, InA, Eco-innovator said...

I'd add a comment or two:

1.) It's misleading to perpetuate that 50*F soil-temp mythg...soil temps (at depth, meaning below about 20' down) vary widely, depending on latitude, climate, slope-orientation...from below freezing to over 90* find out what they are in your area, check into local deep-well water-temps.

2.) It's much cheaper to heat by smartly superinsulating and using
Annualized Geo-Solar (AGS) than to use a heat pump... (I'm currently consulting on a prototype Zero Net Energy house for the Canadian Housing system, based on these techniques and PV... : ) - Don

At 3:13 PM, Anonymous Don Stephens, InA, Eco-innovator said...

For thos wishing to learn more about Annualized Geo-Solar (AGS) there are several pages on my website ( discussing it and/or demonstrating it's application in real-world projects... - Don

At 12:03 PM, Blogger free energy said...

The domestic hot water was being produced from the "Desuperheater" heat exchanger on the ground source heat pump. So the DHW system was simply working as designed,. The user never realized the backup system was switched off precisely because the DHW desuperheater was working very well, thank you!
That was not wasted energy, just recycled energy.
One could come to the opposite conclusion, that the desuperheat coil is an excellent way to make hot water. Superheating can cause the evaporator coil to become partially filled with Freon vapor. You want it filled with low temp. boiling Freon liquid.
So a desuperheater actually IMPROVES performance while recycling the superheat to the DHW loop!
While in may seem expensive to install a retrofit ground contact thermal loop. In new construction, the costs can be amortized over the loan period. The fuel savings allow a quicker pay down, and thus a rapid return on investment. The lifespan of the ground loop is indefinite and it could last 50-100 years or the life of the structure. The cost of the mechanical you may not equipment is not a very large portion of the install costs. The idea that the 20-30% of the energy needed pump and produce 2-4 times as much heat is penalty is not supported by the fact that ground sourced heat pumps are way more efficient than air sourced ones in common use.
Finally, if you super insulate, perhaps with polyimide foam at R-30 per inch, use large enough heat exchangers and augment geothermal with solar thermal and small amounts of solar PV you may not need any grid power at all or any electric heat pump at all to heat and cool a home synergistically.
You are spreading a myth when you assert that geothermal energy is 50°F. There are maps that show you the real temperature. There are real maps at
The Geothermal heat resource is primarily due to the Weak Nuclear Force that warms our planets interior, not solar insolation. It is safe, and has none of the disadvantages of The Strong Nuclear Force energies of fission.
This heat is available everywhere on earth and not to be confused with rare geothermal “Hot Spots”
The idea of running a compressor with no load in the living room misrepresents the actual power consumption , which would be far less than one under load pumping Freon.
I think what you have done here is set up a cynical straw-man argument without bothering to get the facts. So, when you then knock the straw man down, the result is unimpressive due to the logical straw-man fallacy of coming to a conclusion without first obtaining factual data.

f you really genuinely want to get to, and then carefully consider the actual facts, see:


Thermomax Evacuated Heat Pipe Technologies:

Heat Pipe Structure:

Energy Savers Web Sites:

Patrick Ward
15 Dec. 2006

With Best regards
Patrick Ward
Richmond VA

At 3:51 PM, Blogger J said...

Free Energy,

Hello. We mostly agree. I agree that geothermal’s operating efficiency beats conventional hot air systems. This blog does not recommend conventional fossil systems so we are on the same side there. You, Don, and I all agree on the importance of good insulation to reduce or eliminate active heating. We agree that reclamators/heat exchangers recycle “waste energy” or under-used capacity by design. The hot water was either waste heat from air-conditioning mode or “intentional” heating from the heat pump/desuperheater so we agree that and we agree that those produce a lot of electric heat. I specified “under load” in the living room so you might have misread that line (no big deal). The MD showcase measured almost exactly 50 degrees and your page also uses the 50-degree shorthand (“In winter, it's much easier to capture heat from the soil at a moderate 50 º F. than from the atmosphere when the air temperature is below zero.”) but I edited the post to clarify. Personally, I am still interested in seeing more performance comparisons of many different systems including passive geothermal (as I mentioned in the post).

Thank you for the comments and please visit again.

At 3:53 PM, Blogger J said...


Hello. I clarified the post about temperature. Your AGS is remarkably close to what I have been leaning toward so far.

Thank you for the comments and please visit again.

At 3:14 PM, Anonymous Anonymous said...

On a recent "This Old House" episode a rehabbed Boston area Victorian was featured. They installed a deep-well source heat exchanger that cost $350k to install but costs only $150 a month to heat/cool almost 10,000 sq ft of living space in the main house and 4 attached condos. The wells were OVER 1000 FEET DEEP and the water a constant 57 degrees.


At 11:44 AM, Anonymous Drew Smith said...

If your goal is to have an affordable home that is inexpensive to heat/cool then you need to learn about Zero Energy Design. You can Google Zero Energy Design and learn tons! But a warning - be prepared to get very frustrated as you'll learn that with the use of 2 exterior walls (two delta T's are MUCH better than one Delta T) and the correct orientation on the Sun, Solid North Facing walls free of as many windows and doors as possible and South Facing walls with Windows and correctly designed over hangs on the south you can build a home with the need for a furnace or A/C at $100 per square foot and it DOESN'T look weird. Our country can save BILLIONS - if we just built more intelligently. Architects are mostly to blame - actually - those who teach architects are to blame the most. Just about every home you look at will look different after you learn about zero energy design. If you're looking for the key to saving energy and money in housing - that's your key. Learn more and Share your knowledge!

At 4:32 PM, Blogger J at IHB and HFF said...

Jim, thank you for the numbers (57 degrees, $350k install, I am not sure if $150 meant winter months or averaged over all 12 months).

Drew, I like earth-sheltered designs as passive geothermal to reduce delta-T.

At 5:27 PM, Anonymous Anonymous said...

I have had 2 homes now with geothermal heat and cooling both in Ohio both in rural areas retrofitted old house for about a $4000 premium over a propane powered system dropped my all electric house from $200/mo ave. to $120/mo ave. That's $80/mo. so by my calculator says I pay back on that over propane was 50 months. after that I had real savings and more consistant price of fuel vs. propane. This house was about 2200sq. ft.

New home built in 2006 average all electric home is running right at $130 to $140 per month average. For a nearly 2700sq ft. with a basement so almost 5400 sq. ft. Obviously tighter home and more insulation then old home but still I'm sold on geothermal heat.

At 1:16 PM, Blogger Mikes said...

Roughly one quarter of North America is capable of supporting any actively heated sites, such as those where hot springs are naturally found. The central and eastern part of the country are still able to use geothermal energy to heat and cool homes and businesses, but their options are limited to passive technologies such as the heat pump.

New York City Hvac contractors

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At 7:03 PM, Blogger katrina said...

if you are running a heat pump with a heat exchanger to your dhw, it is not the heat of the compressor or "waste heat" generated by electric that heats the domestic hot water. it is the heat that is being pumped from your house. in a mild climate, this could go on year round if there is a load in your house for cooling. it is your bodily heat and the waste heat of appliances in your home that is heating your dhw. so throw that argument out as an "against" and make it a "for".

that would not work year round in chicago, since sooner or later you would be in full heating mode and want to reject that superheat into your house, and probably need to supplement with electric.

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At 9:00 PM, Anonymous Dan T. Annda said...

Your argument is based on getting 5% from Money Markets. Perhaps in Ireland or Greece you can get 5% back, but in the USA, the highest Money Market Account will pay you .95%., a site which is much more trustworthy than the Federal fictions, puts inflation at 6%, so if you have your money in a MMA, you are losing 5% a year.

Now, who's the smart guy, eh?

At 6:23 PM, Anonymous Anonymous said...

We just purchased a house with geo thermal heat this summer and were very happy with everything. Until winter came around. Our power bill is about $ 1000,00 to 1300 Dollars every month. Nobody seems to be able to figure out why. HELP !!! We can't afford that. Any suggestions what could be the problem with our geo thermal system.
Thanks. Anja from Saskatchewan.

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At 10:56 PM, Blogger Heating Ontario said...

Geothermal heating provides many benefits especially to homes and buildings. The fact that the energy it uses comes from nature makes it very appealing to homeowners.

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At 9:28 PM, Anonymous Anonymous said...

So, as someone who wishes to someday build a Zero Energy home which combines several different sources, if I'm willing to pay the upfront costs of installation, is geothermal a good way to go? My dream home is a monolithic dome style, south facing with large windows, sod roofed structure. Additionally, it will be partially earth bermed. Most, if not all of my electricity needs will be supplied by solar panels, although I don't want to use them for heating and cooling the structure.

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