Geothermal Cost Per Month: What It Actually Costs to Run

The short version: a geothermal heat pump has no fuel bill, but it does have an electric bill, and that bill is its principal routine running cost. What you pay per month is a function of three things you can actually look up: how much heating and cooling your house needs, how efficiently your unit converts electricity into that heating and cooling, and what your utility charges per kilowatt-hour. The US average residential electricity price was 18.44 cents per kWh in May 2026 (EIA, preliminary). Everything else is arithmetic — and doing that arithmetic for your own house beats any national average you will find, including ours.

"What does geothermal cost per month" resolves differently for almost every household — a single figure hides exactly the variables that decide whether the answer is good news for you. So: the calculation, not a number.

The Only Formula You Need

Monthly operating cost comes down to:

The part that requires thought is the first term. A geothermal heat pump's electricity use is its heat output divided by its efficiency, which is why the efficiency rating is the number that does the work.

A worked example. Suppose a house has a heating design load of 40,000 BTU per hour, the heat pump runs an average of 10 hours a day through a cold month, and the unit operates at a COP of 3.6 — the current ENERGY STAR minimum for closed-loop water-to-air equipment.

• 40,000 BTU/hr ÷ 3.6 = 11,111 BTU/hr of electricity input
• 11,111 ÷ 3,412 BTU per kWh = 3.26 kWh per hour of runtime
• 3.26 kWh × 10 hours = 32.6 kWh per day × $0.1844 = $6.01 per day
• Across a 30-day cold month: about $180 for heating

Two things about that number. First, it is a peak-season figure — it assumes the coldest stretch, when the system runs hardest. Shoulder months cost a fraction of it, which is why an annual average is much lower than a January bill. Second, runtime hours are the term most people guess at, and guessing wrong moves the answer proportionally: at 5 hours a day, the same house and the same unit cost half as much. The point of the example is the method — swap in your house's design load, your realistic runtime, and your actual rate.

Now the summer version, because for a lot of the country cooling is the bill that hurts. Cooling uses EER rather than COP, and EER is already expressed in BTU per watt-hour — so there is no 3,412 conversion step, which trips people up. Take a 3-ton cooling load (36,000 BTU/hr) on a unit at the ENERGY STAR closed-loop water-to-air minimum of 17.1 EER, running 8 hours a day:

• 36,000 BTU/hr ÷ 17.1 = 2,105 watts, or 2.11 kWh per hour of runtime
• 2.11 kWh × 8 hours = 16.84 kWh/day × $0.1844 = $3.11 per day
• Across a 30-day hot month: about $93 for cooling

The same caveats apply — that is a peak-month figure at an assumed runtime, and a unit rated above the ENERGY STAR floor costs proportionally less to run. But it shows why geothermal's cooling story is usually the easier sell: you are running one machine, not a furnace in winter and a separate air conditioner in summer, and the summer number is the one that arrives during the year's highest electric rates in much of the country.

For a whole-house reference point: EIA reports that the average US residential utility customer purchased 10,791 kWh in 2022, about 899 kWh per month. Applying today's average price to that usage gives roughly $166/month — an order-of-magnitude marker, not an observed bill (the price is 2026's, the usage 2022's). EIA notes that purchase figures understate consumption for households with on-site solar.

What Actually Drives Your Number

Four variables account for most of the variation between two homeowners with the same equipment.

1. Your electricity rate

This is a large lever and the one you least control. The national average is 18.44¢/kWh, but the spread between the cheapest and most expensive states is large enough to change geothermal's economic case. A system that costs $60/month to run in a low-rate state costs well over $100 in a high-rate one, with identical equipment and identical weather.

2. Your climate and your house

Heating and cooling load is a property of the building, not the system. Insulation, air sealing, window area, and square footage set how much energy has to be moved; the heat pump only determines how efficiently it gets moved. This is why efficiency upgrades to the envelope reduce a geothermal bill just as they would any other system's.

3. Your unit's actual efficiency

Not the number on the brochure — the number at your operating conditions. See the next section.

4. What else is on the meter

Geothermal moves your heating cost onto the electric bill. If you switched from gas or oil, your electric bill goes up while a different bill goes down or disappears. Comparing your new electric bill to your old electric bill is the most common mistake in judging whether geothermal is saving you money — the comparison that matters is total household energy spending.

The Efficiency Ratings That Matter

Two numbers govern operating cost, and both appear on the equipment's certification.

COP (Coefficient of Performance) measures heating: units of heat delivered per unit of electricity consumed. A COP of 3.6 means 3.6 units of heat out per unit of electricity in.

EER (Energy Efficiency Ratio) measures cooling: BTU of cooling per watt-hour of electricity.

Current ENERGY STAR minimums for residential geothermal heat pumps, from the Version 3.2 specification:

Two things to take from that table. First, open-loop systems carry higher minimums than closed-loop ones — the usual explanation is that well water arrives at a more favorable temperature than fluid circulated through buried pipe, though the spec itself doesn't say. Second, and more practically: water-to-water minimums are lower than water-to-air, so "the ENERGY STAR minimum" is not one number. Check which category your equipment falls in before comparing. Our open-loop vs. closed-loop guide covers the trade-offs, which include considerations well beyond efficiency.

The Costs That Aren't Electricity

Operating cost is not only the power bill. The recurring non-electricity costs of a geothermal system are genuinely modest, but they are not zero:

• Air filters — the same consumable as any forced-air system, on the same schedule.
• Annual service — inspection, flow check, and coil cleaning. Our maintenance guide covers what a visit should include.
• Loop fluid and antifreeze checks — infrequent, but part of the long-run picture.
• The circulating pump — a wear component with a service life shorter than the loop's.
• Eventual equipment replacement — not a monthly cost, but the indoor unit wears out while the loop does not. What that costs is covered in our replacement guide.

Nobody publishes a credible, current, nationally representative figure for what US households actually spend maintaining a geothermal system. Contractor quotes and content sites put numbers on it, but those are not survey data and they disagree with each other. The number that will govern your budget is a local service contract quote, and there is no national average that beats getting one.

Why Published Averages Mislead

Search this question and you will find confident monthly figures — "$50 to $100 a month," and similar. Treat them carefully, for three reasons.

They rarely state the electricity rate they assume. A monthly cost figure without a ¢/kWh assumption is not a result; it is a number. Rates vary enough across states that the same system produces very different bills.

They rarely state the house. Square footage, climate zone, and envelope quality change the load by multiples. An average across all US homes describes no particular home.

They often quietly compare the wrong things. A geothermal electric bill compared against a pre-geothermal electric bill will always look bad, because the heating load moved onto that meter. The comparison that answers the real question is total annual energy spending before and after.

If you want a number for your own house, the path is: pull your annual kWh from twelve months of bills, find your all-in rate, and work from your unit's performance data at your loop conditions. That is more effort than reading an average, and it is the only version that describes your house.

The Bottom Line

The operating-cost case for geothermal is real, and it rests on a simple mechanism: the system moves heat rather than making it, so it delivers several units of heating for each unit of electricity it draws. ENERGY STAR's current minimums put that ratio at 3.6 or better for closed-loop water-to-air equipment and 4.1 for open-loop water-to-air, with somewhat lower thresholds on the water-to-water side.

What that translates to in dollars depends on your rate and your house. Two homeowners with identical equipment can see bills a factor of two apart. Run your own numbers, compare total household energy spending rather than the electric bill alone, and treat any monthly figure that does not disclose its assumed rate as marketing.

For the electricity-specific deep dive — what the system draws, and how that shows up on the meter — see our guide to geothermal electricity usage. For the upfront side of the ledger, the installation cost guide covers what the system costs to put in.