A greenhouse heater holds a minimum temperature through cold weather — protecting tender plants from frost and extending what you can grow into winter. The right heater depends on your greenhouse size, what you’re protecting and whether you have power. Here’s how to choose.
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Heater types
| Type | Pros | Cons |
|---|---|---|
| Electric fan/tube | Clean, thermostatic, dry heat, no fumes | Needs a safe power supply |
| Gas (propane) | Powerful, no mains needed | Produces moisture & fumes; needs ventilation |
| Paraffin | Cheap, simple frost protection | Moisture & fumes; low output; refuelling |
Electric heaters with a built-in thermostat are the easiest to control and keep the air dry (helping prevent disease); gas and paraffin add humidity and need ventilation.
Sizing and thermostats
Match output to your greenhouse volume and target temperature — an undersized heater won’t hold frost off in a cold snap. A thermostat (built-in or separate) is essential so the heater only runs when needed, saving running costs. For frost-free growing you only need to hold a few degrees above freezing.
Electric greenhouse heaters
Thermostats & controllers
Safety & running costs
Follow the manufacturer’s safety guidance — keep heaters clear of foliage, use outdoor-rated electrics, and ventilate fuel-burning heaters. A thermostat and good insulation (bubble wrap on the glazing) cut running costs. See how to heat a greenhouse and frost protection.
Quick questions
What size greenhouse heater do I need? Match it to your greenhouse volume and the minimum temperature you want to hold; err larger for cold climates and use a thermostat.
Choose by your heating objective
- Frost-free only — hold a few degrees above freezing to overwinter tender plants; a modest thermostatic electric heater is enough and cheapest to run.
- Active winter growth — holding a warm minimum for tropicals costs far more; size up and insulate heavily first.
Sizing and energy
Match heater output to greenhouse volume and your target minimum — there is no single wattage-per-area rule (glazing, insulation and climate all change it). Insulate with bubble wrap, run a thermostat so it only fires when needed, and heat only the zone you need.
Pair it with a thermostat/controller
An accurate thermostat/controller stops any heater running needlessly — the single biggest cut to running cost, and the difference between a steady minimum and wasted energy.