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Commercial · Greenhouses & Garden CentresGreenhouse & Garden Centre Heating
Greenhouse and garden centre heating is best done with separated-combustion gas unit heaters built with stainless steel heat exchangers, because greenhouse air is wet, carries fertilizer and pesticide vapour, and rusts through a standard heater's exchanger early. The second rule is redundancy: two heaters sharing the load protect a crop better than one large one, since a single failure on a cold night no longer means a frozen house. We install, pipe and service greenhouse heaters for growers and garden centres from Flamborough and Milton to Caledon, on natural gas or propane.
The heater has to survive the air it sits in. A separated-combustion unit pipes its combustion air in from outdoors and its flue gas back out, so the burner never breathes greenhouse air, and a stainless heat exchanger resists the condensation that forms on every cold start. This matters for the plants as well as the equipment. A corroded or cracked exchanger leaks flue products into the house, and ethylene from incomplete combustion distorts leaves and drops flowers at concentrations far too low for a person to notice.
A tight poly house also starves an ordinary heater of air. Double-layer inflated poly loses roughly a third less heat than a single layer, which is why growers use it, but it leaks so little that an open-combustion burner can run short of oxygen and start producing carbon monoxide and ethylene. Sealed combustion removes that risk. Unvented heaters that discharge into the growing space are the wrong tool for the same reason, however cheap they look in a catalogue.
Heat only works if the air is moving and the controls agree with each other. Horizontal airflow fans circulate air in a slow loop down one side of the house and back up the other, and the heater should discharge along that loop, not across it. Heating, vents and exhaust fans are staged from one controller with a dead band between them, and the heaters are interlocked off whenever a ventilation stage is open. Without that interlock, a sunny March morning has the vents cooling the house while the burners try to heat it.
Gas supply decides the schedule. A detached house 60 metres from the meter needs a line sized under CSA B149.1 for its length and total load, often run at higher pressure with a regulator at each heater, and several new heaters can exceed what the existing Enbridge meter and service will deliver. On rural lots in Flamborough, Lowville, Kilbride, Carlisle, Campbellville and Caledon where no gas main reaches, the same heaters are ordered for propane. Larger open retail areas are closer to our warehouse and industrial heating work, and the commercial HVAC hub lists the rest.
Equipment we install and service
Suspended, fan-type heaters with sealed combustion and a stainless steel heat exchanger, vented through the end wall or roof. We hang them clear of the poly, aim them down the airflow loop and pipe the intake and vent to the manufacturer's clearances. Repairs and replacements for standard models are covered on our commercial unit heater page.
Small circulation fans hung above the crop that keep temperature even from end to end and keep leaves dry. They run continuously in the heating season. A dead fan shows up as a cold corner and disease in the same spot every year.
Roof or side vents and end-wall exhaust fans, staged by temperature from one controller along with the heat. The sensor belongs at plant height in a shaded, aspirated box; a bare thermostat on a sunlit post reads high and shuts the heat off early. We wire the heater interlock and set the dead band.
Steel or approved polyethylene underground line from the meter or tank to each house, with risers, shut-offs and a regulator at each appliance. Sizing is calculated for the full connected load so the last heater on the run still sees correct pressure when every burner fires at once. See gas line installation.
What goes wrong in these buildings
- The heater in the far house fires, drops out and relights all night when everything is running.
- We replaced a rusted-out unit heater a few winters ago and the new one is already flaking.
- Tomato leaves are curling near the heater and nobody can tell me why.
- The vents were wide open and the heater was running at the same time, and I am paying for both.
- It is the first week of March, the plugs arrive Monday and one heater will not light.
- Enbridge says our meter is too small for the two houses we just put up.
How it works
We calculate heat loss from the covering, the surface area and the lowest night temperature you need to hold against, then add up connected load and measure the run to the meter or tank. If the meter or service is short, the load request to Enbridge goes in first, since that part of the timeline is not in our hands.
Heaters, venting, gas line and controls are installed and pressure-tested in fall or early winter, before the houses are full. Gas work is done by TSSA-licensed technicians. Cost follows the number of heaters, the length and size of the gas run, trenching and any service upgrade, so it is quoted in writing after a site walk; our pricing page covers the general bands.
Before the first firing we clean burners and intake screens, inspect the exchanger, check venting, test the fan and safeties, and verify gas pressure with all heaters running. Book it for January if you fire in February. For a heater down with a crop in the house, call (647) 801-1252 or reach the shop.
Common questions
What size heater does a greenhouse need?
It depends on three things: the surface area of the covering, the type of covering, and the difference between your night setpoint and the coldest outdoor temperature you plan for. Glass and single poly lose the most; double inflated poly and twin-wall polycarbonate lose less. We calculate it per house and then split the total across two heaters where the layout allows, so one failure does not cost the crop.
Can I use a standard unit heater instead of a separated-combustion one?
It will heat the house, and it will fail early. A standard heater draws humid, chemical-laden greenhouse air through the burner, which corrodes an aluminized steel exchanger and can leave the burner short of air in a tight house. The price gap between the two is small next to a replacement heater and a damaged crop. In an open, well-ventilated retail canopy the answer can be different.
When should greenhouse heaters be serviced?
Once a year, four to six weeks before you first fire them. For bedding-plant growers that usually means January. Heaters that sat idle since May collect spider webs in the burner orifices, rust flake on the burners and debris in the intake, and every one of those causes a failed ignition on the first cold night. A mid-season check is worth it if a heater has been short-cycling.
We are adding a second greenhouse. Will our gas service handle it?
Add the input ratings of every gas appliance on the meter, old and new, and compare the total to the meter's capacity; we do this as part of the quote. If the total is over, Enbridge has to upgrade the meter or service, and that request should go in months before you need heat. Long runs to detached houses are sized separately for pressure drop. On propane, the check is tank size and regulator capacity.
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