Heating a small greenhouse through a Canadian winter is one of the most consequential decisions a backyard grower makes, because it determines both what can be grown and how much it costs to grow it. A structure that works fine in October becomes expensive to maintain in January in northern Alberta, and the heating approach that suits a grower in coastal British Columbia may be impractical in Quebec.
The options below cover the most common approaches used in non-commercial backyard greenhouses across Canada, with notes on how each performs at different temperature extremes.
Passive Solar and Thermal Mass
Before adding any active heat source, it is worth considering how much heat a greenhouse can retain and generate on its own. A well-oriented greenhouse — long axis running east to west, with the main glazed wall facing south — can collect substantial solar gain during daylight hours even in midwinter.
Thermal mass amplifies this. Water barrels, large containers filled with water, stone flooring, or concrete block interior walls all absorb heat during the day and release it slowly at night. A greenhouse in southern Ontario with 200 litres of water in dark-coloured barrels can stay several degrees above outdoor nighttime temperatures through passive means alone, which may be sufficient for storing root vegetables or overwintering dormant perennials.
Passive solar alone is not sufficient for growing warm-season crops or for climates where overnight temperatures drop below −15°C regularly. It reduces heating costs when combined with active heating and is worth prioritising during the design phase.
Orienting a greenhouse with its ridge running east to west and the main glazed face towards true south (not magnetic south) can increase passive solar gain by 20 to 35 percent compared to an arbitrary orientation.
Electric Heating
Electric heaters — either forced-air fan heaters or radiant panel heaters — are the simplest heating option for small greenhouses. They require only a weatherproof electrical connection, have no combustion exhaust to manage, and are straightforward to wire to a thermostat.
The problem in most of Canada is cost. Electricity rates in Ontario, Nova Scotia, and British Columbia range from roughly $0.14 to $0.20 per kWh. Running a 2 kW heater continuously costs $0.28 to $0.40 per hour. A small greenhouse in a cold winter might require 12 to 16 hours of heating per day, which adds up quickly over a four-month winter.
Electric heating makes more financial sense in provinces where electricity is inexpensive — Manitoba and Quebec are notable examples, with rates around $0.07 to $0.08 per kWh. Growers in those provinces can often heat a small greenhouse for less per season than growers in Ontario using propane.
Propane Heaters
Vented propane heaters are widely used in hobby greenhouses across rural Canada where natural gas is not available. A 30,000 BTU propane heater is a common size for a greenhouse between 15 and 30 square metres. Propane is energy-dense, the heaters are reliable, and refilling a 100-pound cylinder is straightforward in most areas.
Venting is important. Unvented propane heaters produce combustion byproducts including carbon dioxide and water vapour. In a sealed greenhouse, CO2 concentration can rise to levels that, while potentially beneficial for plant growth at moderate levels, cause condensation problems and, at high concentrations, health risks for anyone working inside. Vented units — which draw combustion air from outside and exhaust directly out — avoid this issue entirely and are the recommended option.
Approximate operating cost: a 30,000 BTU propane heater running eight hours a day at 2025 propane prices (roughly $1.10 per litre in most of Canada) costs $15 to $20 per day, or $1,800 to $2,400 over a 120-day heating season.
Natural Gas
Where natural gas is available, it is typically the most cost-effective fuel for greenhouse heating. Natural gas heaters for hobby greenhouses work identically to propane units and many are dual-fuel capable. The challenge is extending a gas line to a detached backyard structure, which requires a licensed plumber or gas fitter in most provinces and involves permit costs. This one-time expense is worth considering if the greenhouse is a permanent structure.
Wood and Biomass
A small wood stove can heat a greenhouse effectively and is sometimes used by growers who have reliable access to firewood. Wood heat requires more active management than other options — a stove needs reloading every few hours — and fire safety considerations in a structure with dry plant material and potentially plastic glazing are real.
Pellet stoves with large hoppers partially address the reloading issue, with some models capable of running 48 to 72 hours between fills. They also burn more cleanly and predictably than cord wood. In areas where wood pellets are reasonably priced, this approach is worth considering for growers who are comfortable with the maintenance requirements.
Geothermal and In-Ground Heating
The Walipini or pit greenhouse design takes the geothermal approach to its logical conclusion by locating the growing area below ground level, where soil temperature remains relatively stable at roughly 8 to 12°C throughout the winter across most of Canada. This design is more common in regions with very cold winters and modest snowfall.
For conventional above-ground greenhouses, in-ground heating pipes — either hydronic tubing buried under the floor connected to a heat source, or a simple earth tube ventilation system — can be added at construction time. The soil thermal mass under the floor acts as a slow-releasing heat buffer. This approach works best as a supplement to another heat source rather than the sole source in climates with sustained cold.
Heat Pumps
Cold-climate heat pumps have improved substantially. Models from manufacturers such as Mitsubishi and Daikin now operate efficiently down to −25°C or −30°C outdoor temperatures, making them viable for greenhouse heating in all but the coldest Canadian locations. A mini-split heat pump delivering 9,000 BTU of heat typically draws about 700W of electricity to do so — a coefficient of performance of around 3.5 to 4, meaning it produces several times more heat per electricity unit than a resistance heater.
The upfront cost of a heat pump system is higher than a simple heater, but in provinces with moderate electricity rates it often has the lowest operating cost over a five-year horizon compared to other options.
Thermostat and Temperature Monitoring
Regardless of which heat source is chosen, a quality thermostat is essential. Analog dial thermostats are adequate; programmable digital thermostats allow nighttime setbacks that reduce operating costs significantly since most crops tolerate lower night temperatures than day temperatures. Wireless temperature sensors with smartphone alerts are available for under $50 and are worth installing to notify growers if the heating system fails overnight.
Environment and Climate Change Canada publishes historical temperature data for most regions through the Climate Data portal, which can be used to estimate how many degree-days of heating a greenhouse in a specific location requires.