Trenches or boreholes for a ground loop

What is the difference in one paragraph?

Both designs bury the same plastic pipe and circulate the same fluid. A horizontal loop lays pipe in trenches a little below the frost line, often in several runs or coils. A vertical loop drops a U-shaped pipe into a drilled borehole and fills the gap around it with grout so heat can flow between pipe and rock. The heat pump does not care which you pick. The site does.

When does a horizontal loop make sense?

It fits rural and large suburban lots with open, diggable soil and room for trenches that stay clear of trees, septic fields and buried services. Excavation equipment is easier to find than a drill rig, so the install can cost less per unit of loop. The weak points are the land requirement and seasonal swings: shallow ground follows the air temperature more closely, so loop fluid can run colder late in winter than it would from deeper ground.

Wet clay or sandy soils change how well the soil conducts heat, so the designer needs a soil description, not just a lot plan. Re-landscaping after trenching is part of the real cost.

When does a vertical loop make sense?

Vertical loops suit small urban lots, retrofits where gardens must survive, and sites where bedrock or poor soil makes trenching awkward. Because boreholes reach depths where temperatures hardly move through the year, performance is steady. The costs are a drilling contractor, a mobile rig on the property, and local rules about drilling and grouting that vary between municipalities and provinces. Ask the installer which authority needs to be notified. The cost reasoning behind this is in geothermal heat pump cost in Canada.

How deep and how far apart?

Vertical boreholes must be spaced so neighbouring holes do not rob each other of heat. For an ordinary house that usually means several metres between holes and a design that sizes total length from the heat load; the working details are in borehole depth and spacing. A storage project plays by different rules. Drake Landing packed 144 boreholes at about 2.25 m centres into a field roughly 35 m across, because the goal was to hold heat in a compact block of ground instead of drawing steadily from it. The full layout is on the borehole storage page.

Other options worth knowing

Some sites use a pond or lake loop, or a slinky coil in a wider trench. Open-loop designs that pump groundwater exist but depend on water quality, quantity and local approval. For most homes the practical choice is between the two main types, and the surrounding trade-offs, such as running cost and lifespan, appear in air source vs ground source.

What does the loop do for the next 30 years?

Whatever type goes in, the loop is a long-lived piece of the property, and the choice has consequences. A horizontal field limits what can be built or planted above it. A vertical field has a small footprint but a hidden geometry that future owners should know about. In both cases the as-built drawing, the pipe diameter, the fluid type and the pressure test results belong in the house file.

Loop design also determines how the system behaves in year ten, not just year one. A loop sized with some margin lets the fluid stay warmer, which helps efficiency (see how ground source heat pumps work), and a tight design leaves little room for the ground to recover. Ask the designer to show the predicted lowest fluid temperature across a multi-year run, not just the first winter.

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