Choosing a greenhouse heater comes down to three things: how cold it gets where you live, how big and well insulated your greenhouse is, and how safely you can power the heater. This guide explains the main ways to heat a winter greenhouse, how to compare each type of greenhouse heater, and which safety checks matter most, with links to browse current options on Amazon.
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Last updated: November 5, 2026
How this guide works
This is a buying and safety guide, not a test report. We explain what each heater type does and what to check, then link to Amazon searches so you can compare current listings, prices and reviews yourself. Always follow the manufacturer’s instructions for any heater you buy. If you are new to growing in winter, start with our guide to the best greenhouse for winter.
Greenhouse heater types compared
| Heater type | Best suited to | What to check before you buy |
|---|---|---|
| Electric fan heater | Small to medium greenhouses with a safe, protected power supply | Rated for damp or greenhouse use, built-in thermostat, overheat and tip-over protection |
| Electric panel or radiant heater | Small spaces where you want steady, quiet warmth | Wattage against greenhouse size, mounting options, protection from water |
| Gas or propane heater | Greenhouses with no power supply | Must be designed for enclosed or greenhouse use; ventilation needs; carbon monoxide alarm |
| Seedling heat mat | Warming trays and pots, not the whole space | Waterproof rating and a separate thermostat |
| Passive heat (water barrels, thermal mass) | Any greenhouse, as a free supplement | Space for barrels; works best in a sunny spot |
How much heat does your greenhouse need?
Start with your coldest realistic night and the lowest temperature your plants can handle. Hardy crops such as many leafy greens tolerate cool conditions, while tender plants need far more protection. A small, well-sealed greenhouse needs much less heat than a large, drafty one.
A minimum and maximum thermometer shows what really happens overnight, and a thermostat lets a heater run only when it is needed. Both are cheap compared with losing a crop, and both help you choose a heater of the right size.
Greenhouse heater safety checklist
- Use equipment designed for greenhouse or damp-location use, and follow the manufacturer’s instructions.
- Power electric heaters from a ground-fault circuit interrupter (GFCI) outlet, and use an outdoor-rated extension cord that suits the heater’s power draw. For permanent wiring, ask a qualified electrician.
- Keep plants, pots, covers and plastic sheeting away from the heater by at least the distance given in the instructions.
- Never run a heater that is not designed for enclosed spaces in a closed greenhouse. Fuel-burning heaters need ventilation and a carbon monoxide alarm.
- Do not leave a heater running unattended unless it is designed for that and has overheat and tip-over protection.
- Check the heater and its cord regularly for damage, moisture and wear.
Ways to need less heat
- Choose a sunny, sheltered spot so the greenhouse gains heat during the day and loses less to wind.
- Seal gaps around the door, vents and base.
- Add inside insulation such as bubble wrap on the covering, without blocking the vents.
- Store heat in water barrels that warm up during sunny hours and release it overnight.
- Cover plants on the coldest nights with frost cloth or row cover.
- Open vents on sunny days and close them at dusk, so the greenhouse does not overheat or lose its stored warmth.
For seasonal jobs outside the greenhouse, see our winter gardening tips and the end-of-season garden cleanup checklist.
What to browse on Amazon
These buttons open Amazon searches so you can compare current listings. They are not product endorsements. Read the full listing, the safety information and recent reviews before you buy.
Which option suits you?
- Small greenhouse with safe power nearby: a thermostat-controlled electric heater designed for greenhouse or damp use is usually the simplest start.
- Mostly seedlings and cuttings: a heat mat with its own thermostat warms the pots without heating the whole space.
- No power supply: focus first on insulation, water barrels and covers; consider a gas heater only if it is designed for enclosed spaces and you can ventilate and fit a carbon monoxide alarm.
- Mild winters: you may need only a thermometer, covers and good venting.
Frequently asked questions about greenhouse heaters
What is the best heater for a greenhouse?
There is no single best greenhouse heater. The right choice depends on your greenhouse size, your coldest nights and your power supply. For many small greenhouses with safe power, a thermostat-controlled electric heater made for greenhouse or damp use is the simplest option. Check the listing for the size or area the maker recommends.
Can I heat a greenhouse without electricity?
You can reduce the cold with a sunny, sheltered position, insulation, water barrels and covers over plants. Gas heaters designed for enclosed spaces exist, but they need ventilation and a carbon monoxide alarm. In a hard freeze an unheated greenhouse can still drop to freezing.
How warm should a greenhouse be in winter?
It depends on what you grow. Hardy crops tolerate cool conditions, while tender plants need protection from freezing. Look up the minimum temperature for each plant and set your thermostat above it.
Is it safe to leave a greenhouse heater on overnight?
Only if the heater is designed for continuous or unattended use, has overheat and tip-over protection, is powered safely and is used exactly as the manufacturer describes. If you are unsure, do not leave it running.
Do I need a thermometer in my greenhouse?
Yes. A minimum and maximum thermometer shows the real overnight low, which tells you whether you need more insulation or a heater at all.