How Does a Geothermal Heat Pump Actually Work?
A geothermal heat pump moves heat instead of making it. Water circulates through pipe buried in your yard, picks up heat from the ground in winter, and dumps heat into the ground in summer. A refrigerant cycle inside the house concentrates it.
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That is the whole machine in four sentences. The part that trips people up is the word geothermal, so let me clear that up first, because it is the most common mixup I get on the phone.
This is not volcano heat. Power plants in Iceland drill miles down to reach the heat of the earth itself. Your house does nothing of the kind. A residential geothermal heat pump uses shallow ground, a few feet down for a trench or a few hundred feet for a bore, and that ground is warmed by the sun, not the core. All you are borrowing is the fact that dirt has a long memory.
Why the ground beats the air in July and in January
Air temperature in central Oklahoma is violent. We swing from 110 in August to single digits in a January cold snap, sometimes with a 40 degree drop inside one afternoon. An ordinary air conditioner has to dump your home’s heat into 105 degree air, and an ordinary heat pump has to pull heat out of 12 degree air. Both are fighting.
Go down past about six feet and the daily swings stop. Go a little deeper and the seasonal swings stop too. What is left is close to the yearly average temperature for your part of the state, and in central Oklahoma that lands right around 60 degrees. In January the dirt under your yard is far warmer than the air. In July it is far cooler. The ground never gets the memo about the weather, and that is the entire advantage.
- In a January cold snap
- Air can be near zero. Ground at loop depth is near 60 degrees.
- On a 105 degree afternoon
- Ground at loop depth is still near 60 degrees.
- What the system trades with
- The ground, every day of the year, not the air.
Moving heat is not the same as making heat
A furnace makes heat. It burns gas or propane and turns that fuel into warmth. It can be very good at that, but it can never give you more energy than the fuel it burned. That is a wall you cannot climb.
A heat pump does not make heat at all. It spends a little electricity to relocate heat that already exists somewhere else. Your refrigerator has done this in your kitchen for years: it does not create cold, it moves heat out of the box and dumps it out the back. A geothermal heat pump is the same trick at house scale, with the ground as the other side of the trade.
Because it is moving heat instead of manufacturing it, the arithmetic looks wrong the first time you see it. A geothermal unit running well returns about $4.50 of heat for every $1 of electricity it consumes. No furnace can do that, no matter how efficient the burner is, because a furnace is playing a different game.
What is actually in the pipe, and what is in the box
Two separate loops, and people mix them up constantly.
- The ground loop
- Buried plastic pipe carrying water with antifreeze. No refrigerant is ever in your yard.
- The refrigerant cycle
- Sealed inside the indoor unit. It never leaves the cabinet.
- Where the equipment sits
- Inside. A closet, basement, or mechanical room. There is no outdoor unit.
The buried loop just shuttles temperature back and forth. It comes into the house slightly warmer than it left in the winter, and the machine’s job is to take that mild bump and concentrate it into air hot enough to heat a room. That concentrating step is what the compressor and the refrigerant do, and it is where the electricity goes.
In summer the whole thing runs backwards. The system pulls heat out of your indoor air and pushes it into the ground instead of into the afternoon. Same equipment, same pipe, opposite direction.
What this means, and what it does not
It means no combustion at your house. No flame, no flue, no exhaust, and nothing burning to produce carbon monoxide. It means no outdoor unit, so nothing sitting beside the house making noise or corroding in the weather. It means no defrost cycle, because there is no outdoor coil to ice up, so you never get that blast of cool air indoors while an air-source unit de-ices itself.
It does not mean free heat. It runs on electricity, and it will show up on your power bill. It does not mean the system is exempt from the rules of a good install either. Geothermal is two systems that have to agree with each other, the loop and the equipment, and a beautiful machine on an undersized loop will disappoint you every day for twenty years.
It also costs more up front than a conventional system. I sell it as a premium system, because that is what it is. See how I do geothermal, or read the honest math on whether geothermal is worth it in Oklahoma.
Common questions about how geothermal works
Does a geothermal heat pump use the earth’s core heat?
No. That is deep geothermal, the kind that runs power plants. Your system uses shallow ground warmed by the sun, from a few feet down for a horizontal loop to a few hundred feet for a vertical bore.
Is there refrigerant buried in my yard?
No. The buried loop carries water with antifreeze in it. The refrigerant stays sealed inside the unit in the house.
What does COP mean on a geothermal heat pump?
Coefficient of Performance is heat delivered divided by electricity consumed. At COP 4.5 you are getting about $4.50 of heat for every $1 of electricity. A furnace cannot exceed 1.0 by that measure, because it is burning fuel rather than moving heat.
Where does the outdoor unit go?
There is not one. All the equipment lives inside, which is why there is nothing beside the house to hear, to hail-dent, or to trip over.
Does geothermal work in an Oklahoma ice storm?
The ground does not care about ice, so the system does not lose capacity the way an air-source unit does in the cold. What it does need is electricity. If the power goes out, it stops, same as any electric system.
Is a geothermal heat pump the same as a regular heat pump?
Same principle, different partner. An air-source heat pump trades heat with outdoor air, which is brutal here in both directions. A geothermal heat pump trades with ground that sits near 60 degrees year round.
Want to know if your property can take a loop?
I look at the house and the ground together, then tell you straight whether geothermal fits. Estimates on a new system are free.
New system estimates are free. Geothermal is statewide across Oklahoma, not just my seven daily service counties.