Best Greenhouse Heaters to Beat Frost (2026 Buying Guide)
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For most small hobby greenhouses with power, the Bio Green Palma is the best heater: a 1,500-watt fan heater with a built-in thermostat and splash-resistant design. The Dr Infrared Greenhouse Heater is a strong alternative, the Mr. Heater Big Buddy works where there is no electricity, and a seedling heat mat is the cheapest way to keep young plants warm.
An unheated greenhouse protects plants from wind and light frost, but a single clear, cold night can still kill tender seedlings, citrus and overwintering cuttings. A small heater with a reliable thermostat keeps the air just above freezing, which is often all you need.
Greenhouses are humid, so ordinary space heaters are not a good idea. Look for models built for damp spaces, with a thermostat and tip-over or overheat protection, and size the heater to your greenhouse instead of guessing.
We compared popular greenhouse heaters on power, safety features, suitability for humid conditions and the kind of greenhouse each one suits.
By NovaAgri Team · Updated November 2026 · Researched from manufacturer specs and owner feedback
Our quick picks
- Best overallBio Green Palma Greenhouse Heater
- Best alternativeDr Infrared Greenhouse Heater
- Best without electricityMr. Heater Big Buddy
- Best for seedlingsVIVOSUN Seedling Heat Mat
Comparison at a glance
| Product | Best for | Power source | Output | Thermostat | |
|---|---|---|---|---|---|
| Bio Green Palma Greenhouse Heater Best overall | Small to medium hobby greenhouses with an outlet | Electric | Up to 1,500 W | Yes, built in | Check price → |
| Dr Infrared Greenhouse Heater Best alternative | Greenhouses, garages and workshops | Electric | Up to 1,500 W | Yes, digital | Check price → |
| Mr. Heater Big Buddy Best without electricity | Off-grid greenhouses and emergency backup | Propane | 4,000 to 18,000 BTU | No (3 heat settings) | Check price → |
| VIVOSUN Seedling Heat Mat Best for seedlings | Seed starting and rooting cuttings | Electric | About 17 W | Add-on controller | Check price → |
The best greenhouse heaters, reviewed
Best overall
Bio Green Palma Greenhouse Heater
Best for: Small to medium hobby greenhouses with an outlet
The Palma is designed specifically for greenhouses, with a splash-resistant housing and a thermostat that can hold a frost-free minimum or a warmer setting for tropical plants. Its fan spreads warm air evenly, which reduces cold spots near the glazing.
It is ideal for lean-to and freestanding hobby greenhouses up to roughly 100 to 120 square feet in mild to moderate winters. In very cold climates, pair it with bubble-wrap insulation or a second heater.
What we like
- Built for humid greenhouse conditions
- Thermostat with frost-protection setting
- Fan helps circulate air and reduce disease
Watch out for
- Needs a safe outdoor-rated power supply
- Not enough alone for large or poorly insulated houses
Best alternative
Dr Infrared Greenhouse Heater
Best for: Greenhouses, garages and workshops
Dr Infrared’s greenhouse model is a sturdy fan heater with a digital thermostat and a design intended for damp spaces. It can be hung or placed on the floor, which is handy in tight greenhouses.
It is a good choice if you want one heater that can also move to a garage or shed. Keep it away from direct spray and run its cord through a ground-fault protected outlet.
What we like
- Digital thermostat is easy to read and set
- Can be mounted or used on the floor
- Doubles as a garage or shed heater
Watch out for
- Fan noise is noticeable up close
- Electric running costs add up in long cold spells
Best without electricity
Mr. Heater Big Buddy
Best for: Off-grid greenhouses and emergency backup
The Big Buddy runs on propane and offers three heat settings, so it can protect a greenhouse that has no power. It includes an automatic shut-off if tipped over and a low-oxygen sensor.
Burning propane releases moisture and combustion gases, so leave a vent cracked and never seal the greenhouse completely. It is best as a backup for the coldest nights rather than a heater left running for days.
What we like
- Works anywhere, no outlet needed
- High output for cold snaps
- Tip-over and low-oxygen safety shut-offs
Watch out for
- Needs ventilation while running
- No thermostat, so you must manage it manually
Best for seedlings
VIVOSUN Seedling Heat Mat
Best for: Seed starting and rooting cuttings
If your goal is germinating seeds or rooting cuttings, warming the root zone is far cheaper than heating the whole greenhouse. A standard heat mat fits under a 10 x 20 inch tray and keeps the soil several degrees warmer than the air.
Pair it with a thermostat controller and a probe in the soil to avoid overheating. It will not protect mature plants from frost, so treat it as a seed-starting tool.
What we like
- Very low running cost
- Speeds up germination for peppers, tomatoes and more
- Waterproof and easy to clean
Watch out for
- Does not heat the air
- Best used with a separate thermostat controller
How to choose and size a greenhouse heater
Work out how much heat you need
A quick way to estimate heat loss is: total glazing area in square feet × the temperature difference you want to hold (in °F) × a glazing factor. Use roughly 1.1 for single-layer glass or film and about 0.7 for twin-wall polycarbonate. The answer is in BTU per hour; divide by 3.41 to get watts.
For example, a small greenhouse with 200 square feet of single glazing, held 20°F above a cold night, needs about 200 × 20 × 1.1 = 4,400 BTU per hour, or roughly 1,300 watts.
Electric or propane?
Electric heaters are clean, simple and easy to control with a thermostat, but need a safe outdoor-rated circuit. Propane heaters work anywhere and give more heat, but need ventilation and more attention. Many growers use electric as the main heater and keep propane as a backup.
Insist on safety features
Choose heaters designed for damp locations, with a thermostat, tip-over protection and overheat cut-off. Plug electric heaters into a ground-fault protected (GFCI) outlet, keep cords off wet floors and keep the heater away from plastic and dry plant debris.
Insulate before you heat
Bubble-wrap insulation on the inside of the glazing, sealing gaps around doors and vents, and adding thermal mass such as water barrels can cut your heating needs significantly.
- Measure the glazing area and coldest expected nights
- Choose a heater with a thermostat
- Use a min-max thermometer to check night temperatures
- Add bubble-wrap insulation for winter
- Keep a fan running for air circulation
Pro tip: Place the thermostat or a separate thermometer at plant height, away from the heater. Readings taken right next to the heater make the greenhouse seem warmer than it really is.
Frequently asked questions
What temperature should I keep my greenhouse in winter?
For overwintering hardy plants, keeping the air just above freezing (about 40°F / 4°C) is usually enough. Seedlings and tropical plants need warmer minimums, often 50 to 60°F (10 to 15°C).
Can I use a regular space heater in a greenhouse?
It is not recommended. Greenhouses are humid and often wet, so use a heater designed for damp locations and plug it into a GFCI-protected outlet.
Is propane safe for greenhouse heating?
It can be used with care. Propane combustion releases moisture and gases, so keep some ventilation, use a heater with low-oxygen and tip-over shut-offs, and avoid running it for long periods in a sealed space.
How many watts do I need to heat a small greenhouse?
Many small hobby greenhouses need roughly 750 to 1,500 watts to stay frost-free, depending on size, glazing and how cold it gets. Use the heat-loss formula in this guide for a better estimate.
Do seedling heat mats heat the whole greenhouse?
No. Heat mats warm the soil in trays, which helps germination, but they do not raise the air temperature enough to protect plants from frost.
Final verdict
Choose the Bio Green Palma for most hobby greenhouses, the Dr Infrared if you also want a workshop heater, the Mr. Heater Big Buddy where there is no power and a VIVOSUN heat mat for seed starting.
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