Not free heat from the centre of the earth. A stable temperature a few metres down, and a machine that exploits it far better than one fighting February air.
Below roughly six metres, ground temperature stops following the weather. In southern Ontario it settles around 8 to 10 °C and stays there, summer and winter.
A heat pump's efficiency depends almost entirely on the gap between the temperature it draws from and the temperature it delivers to. An air-source machine on a −20 °C morning is working across an enormous gap. A ground-source machine on the same morning is drawing from 9 °C. That is the whole idea, and it is why the efficiency gap widens exactly when you need heat most.
This is not geothermal power. There is no volcanic heat involved and no free energy. The system runs on electricity — it simply uses much less of it than any alternative, because it has been given an easier job to do.
| Type | How it is built | Suits | The risk |
|---|---|---|---|
| Vertical closed | Boreholes, typically 100–180 m, U-bend pipe, grouted | Constrained sites, commercial and institutional. The default. | Drilling cost and rig access |
| Horizontal closed | Trenched or slinky pipe, 1.5–2.5 m down | Rural and low-rise with land | Needs real acreage; shallower means more seasonal swing |
| Pond or lake | Coiled loop submerged and anchored | Sites with a suitable body of water | Approvals, and the water body must be deep enough not to freeze through |
| Open loop | Groundwater drawn, used, and returned | Good aquifer and a discharge route | Water chemistry, fouling, and the heaviest regulatory burden |
This is the part that separates a designed field from an estimated one.
A loop field is not a heat source. It is a heat battery. Every winter you withdraw heat from the ground, and every summer, if the building also needs cooling, you put heat back. If the withdrawals and deposits roughly balance over the year, the ground returns to where it started and the system performs the same in year twenty as in year one.
A heating-dominated building with an undersized field draws more heat out each winter than the summer puts back. The ground cools, season over season, by a fraction of a degree at a time.
Nothing appears to be wrong for years. Then one cold week the source temperature is low enough that capacity falls short, and the building cannot be heated. The remedy at that point is more boreholes, on an occupied site, at a cost nobody budgeted.
This is the single most common failure mode in Canadian geothermal, and it is entirely a design problem, not an equipment problem.
Buildings with simultaneous heating and cooling — a hotel, a hospital, a mixed-use block with a cold core and a warm perimeter — are the best candidates of all, because the loop moves heat between zones rather than dumping it outside.
Water-to-water or water-to-air heat pumps, a circulating pump set, a buffer tank where the load profile calls for one, and controls. Commercial installations often use distributed units on a common loop, which lets one zone's rejected heat serve another's demand directly.
It can, if the field is undersized for the building's annual balance — heat is withdrawn faster than it is replenished, and the ground cools season over season. A correctly designed field does not have this problem, which is why the design work matters more than the equipment choice.
Vertical bores are typically 100 to 180 metres, and the number is set by the load and the measured thermal conductivity of the ground, not by a rule of thumb.
There is no outdoor unit, which is one of the underrated advantages. The mechanical noise is inside, in a plant room, and neighbours hear nothing at all.
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