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Geothermal vs Air Source

How each system works

An air-source heat pump uses a fan and outdoor coil to exchange heat with outside air. A geothermal system circulates water or antifreeze solution through pipes buried in trenches or vertical boreholes, or through a well or pond, then uses a heat pump indoors to move that heat into the house. Ground temperature a few metres down stays fairly constant through the year, so the geothermal heat pump always works from a moderate source.

Efficiency comparison

Geothermal systems often reach COPs of 3 to 5 year-round because the source stays mild. Air-source units can match that in mild weather but drop in deep cold. In cold climates the seasonal efficiency gap is larger; in mild climates it shrinks. Geothermal ratings use different test standards, so compare carefully with a contractor. See COP explained.

Installation cost and complexity

The ground loop is the main cost. Horizontal loops need large yard areas dug to several feet deep. Vertical loops need drilling rigs and boreholes, sometimes hundreds of feet deep. Costs depend on soil, rock, access and local drilling rates and are often several times an air-source system. Drilling and loop work usually require specialized licensed contractors and permits, and some jurisdictions regulate boreholes to protect groundwater.

Lifespan

Ground loops often last for decades. The indoor heat pump unit typically lasts about as long as or longer than an outdoor air-source unit because it is sheltered. See heat pump lifespan.

Site factors

• Yard size and access for equipment.
• Soil type and bedrock depth.
• Local regulations on drilling and water use.
• Existing landscaping, septic fields or buried utilities.
• For open-loop systems, well water quantity and quality.

Where air-source wins

Lower upfront cost, simpler installation, no excavation and wide contractor availability. Modern cold-climate heat pumps narrow the efficiency gap in many regions. Air-source is also easier to retrofit in small lots and townhouses.

Where geothermal wins

Very low operating cost in cold climates, quiet operation with no outdoor fan unit, long loop life and stable output in extreme cold without much backup. Some systems can also preheat domestic hot water.

Payback thinking

Payback compares the extra installed cost with yearly operating savings. Use the operating cost calculator twice: once with an air-source HSPF2 equivalent and once with a higher seasonal efficiency representing geothermal, then divide the cost difference by the savings. Incentives may change the answer; check Canada or US guidance for where to look, without assuming any amount.

Worked example

Figures below are illustrative examples (2026-10-29), not quotes or guarantees.

A house needs 80 million BTU per heating season. An air-source unit at an average seasonal COP of 2.4 uses about 9,770 kWh; a geothermal unit at COP 3.8 uses about 6,170 kWh. At $0.15/kWh the difference is about $540 per year. If the geothermal system costs $20,000 more installed, simple payback is about 37 years before maintenance and incentives; with cheaper drilling or higher prices it would shorten.

How ground loops work

A geothermal system circulates fluid through buried pipe, either in horizontal trenches or vertical boreholes. The ground a few metres down stays near a steady temperature year-round, so the heat pump draws from a warmer source in winter and rejects heat to a cooler sink in summer than an air-source unit sees. That steady source is why geothermal COP holds up on the coldest days.

Site factors

Horizontal loops need a large area of open land that can be excavated. Vertical boreholes fit small lots but require a drilling rig, access for heavy equipment and attention to local well regulations. Rocky soil, groundwater and setbacks from septic systems all affect feasibility and cost. A site assessment should come before any price comparison.

Lifespan of the parts

The buried loop typically outlasts the indoor heat pump by decades, so a replacement later involves only the indoor unit. Air-source outdoor units are exposed to weather and usually have a shorter service life. When comparing lifetime cost, include the expected replacement of the indoor or outdoor equipment over the period you plan to own the home.

When air-source is the better choice

For many homes, a cold-climate air-source heat pump gets close enough to geothermal performance at a much lower installed cost, especially if the house is well sealed. Geothermal tends to make the most sense for larger homes, very cold climates with high heating loads, new builds where excavation is already happening, or owners planning to stay a long time. Get firm quotes for both before deciding.

Comparing quotes

Ask both contractors for the heating load calculation, expected seasonal efficiency, equipment warranty, loop warranty for geothermal, and an estimate of annual running cost using the same electricity price. Comparing on equal assumptions shows whether the higher upfront geothermal cost is likely to be recovered within your ownership period.

Noise and outdoor space

Geothermal has no outdoor fan unit, which suits tight lots and noise-sensitive neighbours. Air-source units need clear space outside and produce some fan and compressor sound, though modern variable-speed units are quiet at low speed.

Maintenance differences

Geothermal loops need little attention once installed, though the circulating fluid and pumps should be checked periodically. Air-source units need regular outdoor coil cleaning and snow clearance. Both need indoor filter changes and routine refrigerant and electrical checks by a licensed technician.

FAQ

Does geothermal work in cold climates?

Yes; it performs especially well there.

Can I add geothermal to an existing home?

Yes, if the site allows loop installation.

Is geothermal noisy?

No outdoor fan, so it is generally very quiet.

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