Greenhouses lose heat fast on cold nights, so the right setup is usually a mix of insulation, thermal mass, and a heater sized to the space.
If you need the cheapest fix first, stop drafts and cover bare glass before you spend money on a bigger unit; the heater can’t outwork a gap in the door.
Greenhouse Heater Comparison
| Model | Best for | Heat output | Controls and safety | Best for | Price |
|---|---|---|---|---|---|
| DR. INFRARED HEATER 1500W Portable Infrared Heater | Top Pick | 900W to 1500W | Tip-over and overheat protection, timer | Small to medium greenhouses | Why it is here |
| NICETOWN Thermal Insulated Door Curtain | Draft Blocker | — | No electrical controls, draft blocking design | Reducing heat loss at doors | Why it is here |
| Duraflame Electric Fireplace Stove Heater | Decor & Heat | Infrared heat for up to 1,000 sq. ft. | Adjustable thermostat and flame controls | Medium greenhouses with decor needs | Why it is here |
| ThermoMate CZ422NG Natural Gas Tankless Water Heater | Gas-Powered Heat | 113,000 BTU (water heater) | Multiple gas safety protections | Large greenhouses with natural gas radiant systems | Why it is here |
| COSTWAY 24000 BTU Mini Split Air Conditioner & Heater | Large Space Heat | 24,000 BTU | Wifi, remote, voice, timer, child lock | Large greenhouses with 208/230V power | Why it is here |
Best Greenhouse Heating Picks for Winter
DR. INFRARED HEATER 1500W Portable Infrared Heater
NICETOWN Thermal Insulated Door Curtain
Duraflame Electric Fireplace Stove Heater
ThermoMate CZ422NG Natural Gas Tankless Water Heater
COSTWAY 24000 BTU Mini Split Air Conditioner & Heater
Which Way Does Heat Energy Flow In A Greenhouse?
Heat energy always moves from warmer to colder areas, which means your greenhouse loses warmth to the night air, the cold ground beneath, and through its glazing. Understanding this flow is key to choosing the right heating method.
The best way to keep a greenhouse warm starts with controlling these losses. Air leaks around doors and vents let heat escape fast. Cold glazing—single-pane glass or plastic—conducts heat out just like a window. Even the floor can soak up warmth unless it’s insulated or covered.
Infrared heaters work well because they warm the plants and soil directly. Instead of just heating the air, they send heat to objects that then radiate it back, creating a stable environment for your plants. On the other hand, heat pumps shine when you need to keep the whole air volume at a steady temperature, using less electricity to move heat around rather than generate it.
Passive solar heating relies on sunlight’s angle and greenhouse orientation. South-facing exposure catches the low winter sun best. Thermal mass—like water barrels or stone—stores that heat during the day and releases it slowly at night. Draft control seals gaps so warm air doesn’t vanish.
How To Size Heat For Your Greenhouse
An infrared heater can effectively warm a small greenhouse, but sizing matters a lot because heat energy must cover the whole volume and offset losses.
Electric heaters convert nearly all their electrical input into heat. What changes is how that heat reaches your plants: infrared heaters send warmth directly to objects and people, not just the air.
That direct radiation feels stronger near plants and surfaces, especially in drafty spaces where warm air escapes quickly. But infrared won’t warm a large volume effectively by itself—it’s more about targeted comfort than bulk air heating.
As a rule of thumb, small hobby greenhouses up to about 150 square feet usually suit a 1,500-watt plug-in heater, like the DR. INFRARED HEATER 1500W Portable Infrared Indoor and Outdoor Heater. Larger greenhouses need a dedicated heating system that can deliver more power, often requiring 208/230 V electrical service.
| Greenhouse Size | Heater Type | Power | Notes |
|---|---|---|---|
| Up to 150 sq ft | Plug-in infrared heater | 1,500 W | Good for small, insulated greenhouses |
| 150 to 500 sq ft | Mini split or dedicated system | 2,000 to 24,000+ BTU | Needs 208/230 V power; better for permanent setups |
| Over 500 sq ft | Commercial heaters or boilers | Custom sizing | Often uses gas or hydronic systems |
Say your greenhouse is 12 by 14 feet with an 8-foot ceiling—that’s 1,344 cubic feet. On a cold night dropping to 30°F outside, you want to keep it at 50°F, a 20-degree temperature gap. Using roughly 10 watts per square foot for basic insulation, you’d need about 1,680 watts. A 1,500-watt plug-in heater comes close, but adding insulation and a thermostat helps avoid running at full power constantly.
The DR. INFRARED HEATER 1500W excels in compact spaces without needing special wiring. The COSTWAY 24000 BTU Mini Split Air Conditioner & Heater, on the other hand, suits larger greenhouses where permanent installation and higher output matter, using a 208/230 V circuit.
Having a thermostat matters more than raw wattage once your greenhouse is insulated. It prevents wasted energy by switching the heater on only when air temperature drops too low, which is more efficient than running a bigger heater nonstop.
How Long A 20 Lb Tank Lasts Is The Wrong Question Here
The cheapest way to heat a greenhouse depends more on controlling heat loss and using the right power level than on how long a propane tank lasts.
Running cost boils down to a simple formula: for electric heaters, multiply watts by hours and your electricity rate; for fuel heaters, multiply burn rate by hours and fuel price. For example, a 1,500-watt heater running 8 hours a night at 17 cents per kWh uses 12 kWh daily, costing about $2.04.
| Heater | Watts | Per hour | Per day (8 h) | Per month (30 days) |
|---|---|---|---|---|
| 1,500 W heater | 1,500 W | 26¢ | $2.04 | $61.20 |
| 750 W heater | 750 W | 13¢ | $1.02 | $30.60 |
Small fixes can save more energy than switching fuel types. Bubble wrap on walls adds R-3 insulation, cutting radiant heat loss through glass. Sealing door gaps and adding thermal curtains reduce drafts and stop warm air from escaping at night.
Heating only the bench or seedling zone by lowering the thermostat elsewhere saves fuel and electricity. Seedlings tolerate cooler air around them if their root zone stays warm. That’s more efficient than heating the whole greenhouse to the same level.
Old greenhouses can save energy by adding these low-cost fixes before investing in new heaters or switching fuel types. The less heat you lose, the less you spend, no matter how long a 20 lb tank lasts.
What To Buy For Small, Medium, And Large Greenhouses
Infrared heat benefits greenhouses by warming plants and surfaces directly without heating all the air, making it energy efficient where you want targeted warmth. Heat from electric resistance or gas combustion can be transformed into infrared radiation by the heater’s elements or flames, focusing warmth on plant leaves and soil.
A smart thermostat saves energy by adjusting heat output to maintain steady temperatures, avoiding wasteful overshoot or long cold spells. In any home or greenhouse, efficient heating means matching the heat source to the space size and insulation, then controlling it precisely.
For small to medium greenhouses, the DR. INFRARED HEATER 1500W Portable fits best. Its 900W to 1500W power range lets you tune the heat for the space size. You get directional infrared warmth that plants respond well to, plus portability if you move it seasonally. It has built-in timer, tip-over, and overheat protection, which adds safety and convenience.
Large greenhouses need a steadier, whole-space solution. The COSTWAY 24000 BTU Mini Split Air Conditioner & Heater provides that, offering powerful electric heat through ductless distribution. It requires proper electrical service but keeps a large volume evenly warm, which infrared spot heaters can’t do as well.
The NICETOWN Thermal Insulated Door Curtain isn’t a heater but reduces heat loss at drafty entrances. It’s a simple upgrade that complements any heater by cutting edge losses, saving on running costs without extra energy input.
The duraflame Freestanding Electric Fireplace Stove Heater works where you want a decorative look and moderate heat for enclosed spaces. It’s less effective for plants compared to infrared because it warms air and surfaces less directly, so skip it if plant health is your main goal.
Choose the heater type based on greenhouse size, mounting options, and whether you need to move it. Infrared heaters suit smaller, portable setups. Mini splits fit larger, fixed installations. Use door curtains to boost any heater’s efficiency.
| Greenhouse Size | Recommended Heating Solution | Key Feature |
|---|---|---|
| Small (up to 150 sq ft) | DR. INFRARED HEATER 1500W Portable | Directional infrared, portable, safety features |
| Medium (150–300 sq ft) | DR. INFRARED HEATER 1500W Portable | Adjustable power, targeted heat |
| Large (over 300 sq ft) | COSTWAY 24000 BTU Mini Split | Whole-space heating, steady temperature |
| Any size | NICETOWN Thermal Door Curtain | Reduces heat loss at entrances |
| Enclosed, decorative use | duraflame Electric Fireplace | Visual appeal, moderate heat |
What Competitors Leave Out About Greenhouse Safety
Wood stoves heat a greenhouse by radiating warmth from burning wood and convection of hot air, but their open flames and ash require careful placement and venting.
The best way to heat a greenhouse safely and efficiently combines a proper heater with good insulation and ventilation control.
Simple hacks like using thermal insulated door curtains or adding weather stripping around doors and windows reduce heat loss and cut costs considerably.
Insulators such as bubble wrap or horticultural frost cloths applied to glazing help trap radiant heat inside and slow cold air infiltration.
Condensation and high humidity are inherent in greenhouses, so only heaters approved by the manufacturer for damp environments should be used to prevent electrical hazards and corrosion.
Mounting heaters off the ground can protect them from moisture, but only if the model is listed for wall or ceiling installation. Improper mounting risks damage and voids warranty.
More Questions, Answered
Can an infrared heater heat a small greenhouse?
What is the cheapest way to heat a greenhouse?
How do I keep a greenhouse warm without wasting energy?
Which way does heat energy flow in a greenhouse?
Are propane heaters safe in a greenhouse?
How much does it cost to run a 1,500 W greenhouse heater?
What is the most energy efficient way to heat a greenhouse?
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