Best Greenhouse Heater to Get Through Winter

These three stand out in the product table above for different budgets and needs.

Best overall: the Bio Green PHX 2.8/US Phoenix Greenhouse Heater 220-240V, around $300, is our first choice from the table.

View on Amazon

Best value: the Greenhouse Heater with Thermostat, around $90, is the lowest priced of these three.

View on Amazon

Also great: the Greenhouse Heater 1500W with APP Remote Control, around $160, is another strong option with a different set of features.

View on Amazon

Heater output is measured in BTUs, and undersizing is the most common mistake, since a heater that struggles to keep up on the coldest night of the year leaves plants exposed exactly when they need protection most. As a rough starting point, a poorly insulated hobby greenhouse needs roughly 5 to 8 BTUs per square foot for every degree of temperature difference wanted between inside and outside overnight lows, though double wall polycarbonate or added insulation reduces that requirement noticeably. Simple frost protection, keeping the space just above 33 to 35 degrees, requires far less output than actively growing warm season crops through winter at 55 to 65 degrees.

Electric Heaters

Electric fan and convection heaters are the cleanest option, producing no combustion byproducts and pairing easily with a thermostat for precise control. They need a nearby weatherproof power source and cost more to run per BTU than gas in most regions, but they're the simplest choice for a smaller greenhouse already wired for electricity.

Propane Heaters

Propane heaters put out more heat for the money in larger greenhouses and don't depend on the power grid, which matters during winter storms when electricity is most likely to fail. They require proper ventilation to avoid carbon monoxide buildup and moisture accumulation, and a tank refill or exchange adds an ongoing task most electric setups don't have.

Paraffin Heaters

Paraffin heaters are a traditional option for smaller greenhouses without electrical access, burning affordably but releasing more moisture and combustion byproducts into the air than electric models, which makes ventilation just as important as with propane.

A heater with a built in adjustable thermostat cycles on and off automatically as temperatures shift, which saves fuel or electricity compared to a heater running constantly at full output. Pairing any heater with a separate min max thermometer lets a grower check the coldest and warmest points reached overnight, catching problems like a heater that shut off early or a thermostat reading inaccurately before it costs a whole bench of seedlings. Frost alarm thermometers that trigger a visible or audible warning below a set temperature add an extra layer of security for anyone not checking the greenhouse daily through the coldest months.

Fuel burning heaters need real ventilation, since carbon monoxide and excess moisture both build up quickly in a sealed greenhouse, and condensation on glazing can drip onto plants and encourage fungal disease. Position any heater away from direct contact with plant foliage, hanging plastic, or water sources, since electric models in particular need a genuinely waterproof rating given how much humidity a greenhouse holds even in winter. A basic carbon monoxide detector is worth the small cost for any greenhouse running a gas or paraffin heater, especially one attached to or near a home. Safety features like this matter as much as raw output when judging the best greenhouse heater for an enclosed growing space, since a unit that isn't safe to run unattended overnight isn't a practical option no matter how well it warms the air.

Bubble wrap insulation applied to the inside of glazing panels cuts heat loss significantly for very little cost, and thermal mass like water filled barrels absorbs daytime heat and releases it slowly overnight, reducing how hard a heater needs to work. Sealing gaps around doors and vents stops a surprising amount of heat loss that has nothing to do with the heater itself. A timer or thermostat that only runs the heater when temperatures actually drop near the danger point, rather than on a fixed schedule, avoids paying to heat a space that doesn't need it yet.

What is the cheapest way to heat a greenhouse?

Improving insulation with bubble wrap glazing and thermal mass like water barrels reduces heat loss enough that a smaller, less expensive heater can maintain the same temperature that would otherwise need a much larger unit.

What temperature should I keep my greenhouse at in winter?

Simple frost protection only needs the space kept above 33 to 35 degrees, while actively growing tender crops through winter usually calls for maintaining somewhere between 55 and 65 degrees.

Is electric or gas better for heating a greenhouse?

Electric heaters are cleaner and easier to control precisely, while gas and propane heaters generally cost less to run in larger spaces but require proper ventilation to manage moisture and combustion byproducts safely.

How many BTUs do I need to heat a small greenhouse?

A rough starting estimate is 5 to 8 BTUs per square foot for each degree of difference wanted between inside and outside temperatures, adjusted down for a well insulated structure.

Do I need a thermostat with my greenhouse heater?

A built in or separate thermostat is strongly recommended, since it prevents overheating during milder nights and saves significant fuel or electricity compared to running a heater at a constant fixed output.

Can I use a regular space heater in a greenhouse?

Standard indoor space heaters usually aren't rated for the high humidity and moisture a greenhouse holds, so a model specifically rated for damp or outdoor adjacent use is the safer choice.

How do I know if my greenhouse heater is working properly on the coldest nights?

A separate min max thermometer left in the greenhouse overnight shows the actual lowest temperature reached, which is the most reliable way to confirm a heater and thermostat are keeping up during a hard freeze.

Heating a greenhouse doesn't have to mean running a large unit at full power all winter. The best greenhouse heater for most home growers is sized correctly for the space, paired with a working thermostat, and backed up by simple insulation upgrades that reduce how hard it has to work. Whether that means an electric heater for a small backyard structure or a propane setup for a larger space, matching output and fuel type to the actual goal, frost protection or active winter growing, keeps plants alive without an oversized heating bill.