Heating a greenhouse in colder months protects tender plants from frost and opens up winter growing. Because energy isn’t cheap, here’s an A–Z of simple, cost-effective tips to keep things efficient.
26 Simple Ways to Heat a Greenhouse (A–Z)
A — Automatic Temperature Control
Use a greenhouse heater with a built-in thermostat for set-and-forget control. Some electric models (e.g., tubular heaters) need an external thermostat. Traditional paraffin heaters are manual on/off.
B — Bottled Gas (Propane)
Propane gas heaters come in sizes for domestic greenhouses, usually with thermostats and frost-stat settings, push-button ignition, and flame-failure safety.
C — Choose the Right Setpoint
Don’t overheat. For frost-free, aim ~2 °C / 36 °F. For overwintering tender plants or plugs, ~7 °C / 45 °F. Many heaters include a frost-stat to make this easy.
D — Distribute Warm Air
A fan heater helps move warm air evenly, reducing cold spots and stagnant pockets that invite disease.
E — Electric Fan Heaters
Plug-and-play, efficient, and typically thermostat-controlled. The fan quickly circulates heat around the space.
F — Frost-Stat Setting
Look for a frost-stat mode so the heater maintains a temperature just above freezing without constant tweaking.
G — Gas Heat = CO₂ Boost
Gas heaters warm the space and generate plant-friendly CO₂ as a by-product.
H — Heated Trays & Benches
Use propagators, hot benches or heated trays to deliver bottom heat to seeds/seedlings without heating the whole house.
I — Insulate the Structure
Proper insulation can cut heat loss dramatically. Use UV-stabilised bubble insulation (e.g., Heatsheets) rather than household bubble wrap.
J — Just Plug It In
Electric heaters are the easiest to control. Built-in thermostats cycle on/off automatically; fans spread heat evenly.
K — kW Matters
kW (kilowatts) = power draw. 1 kW = 1000 W. Use it to estimate running costs from your electricity tariff.
L — Low-Wattage Background Heat
Electric tubular heaters provide gentle background warmth; pair with a thermostat for control. Use single or multiple in rows.
M — Mend Before Winter
Fix cracked panes and gaps before insulating to prevent draughts (all-weather tape can temporarily seal cracks).
N — Natural Gas Heaters
Natural gas heaters are thermostatic, odour-free and suitable for greenhouse environments.
O — Only Heat What You Use
Group plants and create a partition “zone” with bubble insulation. Heating a smaller zone saves energy.
P — Paraffin Options
Paraffin heaters work where there’s no mains power and add CO₂. Monitor ventilation and moisture.
Q — Quiet Fans
Most electric fan heaters run quietly enough for conservatories or attached garden rooms.
R — Roof Vents Still Matter
Even in winter, occasional venting refreshes air and limits condensation. If insulated, cut neatly around vents so they still open.
S — Save with Fleece
On very cold nights, cover crops with garden fleece to gain a few degrees without cranking the heater. Remove by day for light.
T — Thermometers (Max/Min)
Use a max/min thermometer to see lows/highs and adjust your settings intelligently.
U — Use a Thermostat
Set the heater to kick in only below your chosen threshold — fewer spikes, less waste.
V — Ventilation vs. Condensation
Warm, humid air = fungal risk. Crack a louvre or vent during the day to clear moisture; close again in the evening.
W — Winter Crops
With heat, you can germinate and harvest through winter: try new potatoes for Christmas, lettuce in grow bags or beds, and potted herbs indoors.
X — X Marks the Spot
Place heaters centrally and away from foliage. Floor-level for bench-grown plants, or suspended units in busy houses — avoid blasting plants directly.
Y — Year-Round Use
The same heater that keeps plants frost-free in winter can raise temps for spring seed sowing and propagation.
Z — Zero Degrees = Frost
Frost hits tender growth hardest in spring. Keep things frost-free with insulation, garden fleece, or a heater on frost-stat.