For most new backyard homes in Toronto, the best answer to garden suite heating is a cold-climate heat pump: one system that heats in January, cools in July and keeps the suite independent of the main house. Electric baseboard costs less to install and more to run, and a line from the main house only makes sense on certain lots. As a garden suite builder, we settle this early, because the choice affects the electrical panel, the trenching and your servicing costs. It also decides how much room the mechanical equipment takes inside our garden suite models.
The table below compares the systems Toronto homeowners usually consider for a suite of roughly 250 to 650 sq. ft.
| System | Install cost | Running cost | Cooling included? | Best fit |
|---|---|---|---|---|
| Ducted cold-climate heat pump | Higher | Low | Yes | Suites with room for a small air handler and short duct runs |
| Ductless mini-split heat pump | Medium | Low | Yes | Compact suites and open layouts |
| Electric baseboard | Lowest | Highest | No | Very small suites with little use, or as backup |
| Electric in-floor radiant | Medium | High | No | Bathrooms, or comfort for older occupants |
| Gas or hydronic line from the main house | Varies with distance | Low to medium | No, unless added | Short, clear routes and a main system with spare capacity |
Cold-climate heat pumps for garden suite heating
A heat pump moves heat rather than making it, so it delivers two to three units of heat for every unit of electricity on a typical Toronto winter day. Older models struggled in deep cold. Current cold-climate units are rated to keep heating well below -20°C, which covers Toronto’s design temperature of about -18°C. Most installers still add a small electric backup for the coldest nights.
Sizing matters more in a small building than in a house. The Ontario Building Code requires heating systems to be sized from a room-by-room heat loss calculation (CSA F280), not a rule of thumb. A well-insulated 500 sq. ft. suite can need less heat than the smallest model some manufacturers sell. An oversized unit short-cycles, which wastes energy, leaves cold corners and wears out the compressor sooner. Ask your installer for the calculation and for a unit whose minimum output is close to the suite’s actual load.
Ductless mini-splits work well in compact, open layouts such as a studio. One wall head can handle the main space, with a small electric heater in the bathroom. In a one-bedroom suite with a closed bedroom door, a compact ducted system usually gives more even temperatures, and you do not see a unit on the wall.
Plan where the outdoor unit goes before the drawings are final. It should sit on a stand or wall bracket above typical snow depth, away from the drip line of the roof so ice does not fall on it, and on a side of the suite where its fan will not bother a neighbour or your own bedroom window. A short, direct line set to the indoor unit also keeps efficiency up and installation costs down.
Electric baseboard and radiant floor heating
Electric baseboard is the cheapest system to install and the simplest to maintain. Each room gets its own thermostat, and there is nothing outdoors. The catch is the bill, because baseboard turns one unit of electricity into one unit of heat, so it uses roughly two to three times the electricity of a heat pump for the same warmth. It also does nothing for summer cooling, and a garden suite with large windows can get hot.
Electric radiant floor heating sits between the two in comfort and cost. It is ideal under bathroom tile and pleasant for occupants who feel the cold. As the only heat source for a whole suite it runs about as expensive as baseboard, so most people use it as a comfort layer alongside a heat pump.
Running heat from the main house to a garden suite
Extending the main house’s heating across the yard sounds efficient, but it rarely is. A gas line to a separate furnace needs a trench, a licensed gas fitter and a check that the existing meter and piping can carry the extra load. A hydronic loop from an existing boiler needs insulated buried piping, and the boiler must have spare capacity. Both options tie the suite’s comfort to equipment inside the main house. If you rent the suite, that also means sharing a heating bill with a tenant.
If you are using one of the City of Toronto’s pre-approved garden suite plans, check the mechanical version before you decide. Those plans come in heat pump and forced-air versions, and changing the HVAC design means the plan no longer counts as pre-approved. Picking the version that matches your heating choice at the start avoids a redesign.
Garden suite heating costs, insulation and ventilation
A new garden suite is a new home under the Ontario Building Code, so it must meet the energy efficiency requirements in Supplementary Standard SB-12. In practice that means well-insulated walls and roof, good windows, an airtight envelope and mechanical ventilation, usually through a heat recovery ventilator (HRV). An airtight suite without proper ventilation gets stuffy and damp, so treat the HRV as part of the heating system rather than an extra.
Here is a rough way to estimate what heating will use. Assume a 500 sq. ft. suite built to current code needs about 5,000 kWh of heat over a Toronto winter, based on roughly 3,500 heating degree days. Electric baseboard would use about 5,000 kWh of electricity to deliver that. A cold-climate heat pump with a seasonal efficiency of about 2.5 would use around 2,000 kWh. Multiply each figure by the all-in rate on your Toronto Hydro bill to compare annual costs, and remember that the heat pump also cools in summer. If you plan to rent the suite, ask about a separate meter so the tenant pays for the energy they use. Most Ontario heat pump rebates target existing homes, so check eligibility for a new suite before counting on one.
For a garden suite that someone will live in all year, a correctly sized cold-climate heat pump with an HRV is usually the system that costs the least over its life and keeps the suite independent. Baseboard still makes sense for a tiny suite with light use, and a line from the main house can work on the right lot. Book a free consultation and we will look at your panel, your yard and the route for services before you choose.