Best Greenhouse Heaters (Electric, Propane and Kerosene-Free)

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1. 1
   Best electric greenhouse heaterBio Green Palma (Digital)

   Small hobby greenhouses on a normal 120 V outlet that need frost protection in winter and air circulation in summer.

   $172–$199typical, Oct 2026
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2. 2
   Best budget electricDr. Infrared DR-218 (1,500 W)

   Small greenhouses on a standard 120 V outlet where you want a cheaper alternative to the Bio Green Palma.

   $101–$120typical, Oct 2026
   Amazon Details
3. 3
   Best for larger greenhouses (240 V)Dr. Infrared DR-218 (3,000 W)

   Larger hobby greenhouses with a 240 V / 20 A circuit, at a low cost per watt.

   $99–$130typical, Oct 2026
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4. 4
   Best 240 V with frost modeBio Green Phoenix PHX 2.8

   Mid-size hobby greenhouses that have a 240 V circuit.

   $299–$300typical, Oct 2026
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5. 5
   Best with humidity controlPalram HG1040 Fan Heater

   Palram/Canopia owners who want heating and humidity control from one unit.

   $509typical, Oct 2026
   Dive to Garden Details
6. 6
   Best propane backupMr. Heater Big Buddy (propane)

   Emergency or backup heat for an off-grid or unpowered greenhouse.

   $159–$240typical, Oct 2026
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7. 7
   Best thermostat for 1,500 W heatersbayite BTC211 Temperature Controller

   Running a full 1,500 W greenhouse heater, which needs more headroom than the ITC-308's 10 A.

   $36typical, Oct 2026
   Amazon Details
8. 8
   Best controller for heater plus fan (under 10 A)Inkbird ITC-308 Controller

   Adding a precise thermostat to a plug-in heater, or running a heater and an exhaust fan from one controller.

   $36typical, Oct 2026
   Amazon Details

A greenhouse heater has a harder job than a space heater in a garage: the walls are thin, the air is humid, and plants die if it fails on the coldest night. So we picked on four things: a water-splash rating, a real thermostat, enough output for the house (sized with the formula below, not by guess), and an honest fit with the power you have. We compared manufacturer spec sheets, retailer listings and owner reviews. We haven't run these heaters ourselves; here's how we research.

The best greenhouse heaters

Compare greenhouse heaters and controllers

What size greenhouse heater do I need?

Don't size by floor area alone. University of Alaska Fairbanks Extension (UAF) uses this formula, credited to Kramer (2013), because it accounts for how much glazing the heat escapes through:

U-values from UAF's table (BTU/h per sq ft per °F): single glass, single polycarbonate and fiberglass 1.2; single plastic film 1.25; double film 0.8; double (twin-wall) polycarbonate or acrylic 0.6. Palram's own SUNLITE figures for bare 4 mm twin-wall convert to about 0.67, so a kit like the Palram Mythos sits close to UAF's 0.6. Clear single-wall panels, as on the Hybrid's walls or Snap & Grow, behave like 1.2.

Worked examples: 6x8, 8x12 and 10x12

Our calculation (not a manufacturer figure) assumes a simple gable house: 5 ft eaves with a 7 ft peak for the 6x8, a 7.5 ft peak for the 8x12, and 5.5 ft eaves with an 8 ft peak for the 10x12. Surface area = side walls + end walls + gable triangles + both roof slopes. For the 6x8: 80 + 60 + 12 + 57.7 = about 210 sq ft. The 8x12 comes to about 333 sq ft and the 10x12 to about 401 sq ft. Check your own kit's dimensions; taller houses have more surface.

How to read it: a twin-wall 6x8 that must stay at 40°F on a 0°F night needs a 40°F lift, so 210 × 0.6 × 40 = 5,033 BTU/h, or 1,475 W. One 1,500 W heater just covers it, with no margin. The same house kept at 40°F when it is 20°F outside needs only half that. A single-wall 8x12 needing a 30°F lift is at 11,995 BTU/h, beyond even a 3,000 W heater, so add bubble insulation (see our winter greenhouse guide) or a second heater.

The formula ignores heat lost through the base and floor and through gaps around doors and vents, so UAF's advice applies: a slightly oversized heater is always better than an undersized one, and a backup heater is worth having. Choosing a twin-wall polycarbonate kit halves the heat you need compared with single-wall panels.

How much does it cost to run a greenhouse heater?

Electric heat is simple to price. A 1,500 W heater uses 1.5 kWh per hour it runs. At the US average residential price of 18.31¢/kWh in July 2026 (EIA), that is about $0.27 an hour. Prices vary a lot by state: 14.71¢ in Washington and 48.00¢ in Hawaii in the same month.

(calc at 18.31¢/kWh.) A thermostat cycles the heater on and off, so actual run hours depend on your nights and insulation; the table is the cost of each hour the element is on. Propane compares on burn rate: Mr. Heater lists the Portable Buddy at 0.044 gal/h on 4,000 BTU and 0.099 gal/h on 9,000 BTU. For a full budget, including the kit and base, see what a greenhouse really costs.

Electric vs propane vs gas: which greenhouse heater type?

• Electric fan heaters (most hobby greenhouses). No fumes, no moisture added, easy thermostat control. Limited to about 1,500 W per 120 V circuit, or about 3,000 W on 240 V. Choose IPX4 or better.
• Propane portables. Work without power, so they are good backup. RHS notes that burning gas or paraffin (kerosene) releases water, ethylene and carbon monoxide, so the house must be vented, which cuts the heating effect. RHS considers such heaters useful mainly for plants that tolerate low temperatures. A 1 lb cylinder will not last a winter night on high.
• Vented gas unit heaters. For larger, year-round houses with a gas line, a vented unit such as the Modine Hot Dawg HD30 (24,600 BTU/h output, rated for greenhouses up to 250 sq ft) sends combustion gases outside through a flue. It is a professional install, and the heater alone costs many times a plug-in unit.
• Hardwired electric. A unit heater like the King KBP Series 2 (950 to 6,000 W, wall or ceiling mount) frees floor space and runs on a dedicated circuit, but needs an electrician.

We left kerosene heaters out on purpose: they share propane's combustion problems and add fuel storage and odor.

Greenhouse heater safety: power, cords, clearances and fumes

1. Use a GFCI outlet. Water and electricity meet in a greenhouse. Plug into a GFCI-protected outdoor receptacle and keep plugs above splash level.
2. Skip the extension cord. A 1,500 W heater draws about 12.5 A continuously. Thin or long cords overheat. If the greenhouse is far from an outlet, have an electrician run a weatherproof circuit; for 240 V heaters this is required anyway.
3. Keep clearances. Keep the heater well away (3 ft is the common rule) from plastic film, shade cloth, seed trays and anything that can burn, on a level, non-flammable surface where it cannot be knocked over or sprayed by the hose.
4. Vent combustion heaters, every time. For propane, follow the manual's vent rule (the Big Buddy needs at least 18 sq in open) and never run it in a sealed house overnight. Use a battery carbon monoxide alarm if you enter while it runs. Ethylene can harm sensitive plants, a reason to prefer electric as the main heater.
5. Measure where the plants are. RHS warns that built-in thermostat dials can be a few degrees off because they sit close to the heater. Put a max/min thermometer or a WiFi sensor such as the Govee H5179 at plant height in the middle of the house; it can alert your phone before the house freezes.

Heat mats: the cheaper way to heat seedlings

If you only need warmth for seed starting in spring, heating the soil is far cheaper than heating the air. Hydrofarm says Jump Start mats warm the root zone 10 to 20°F above the surrounding air, and Bootstrap Farmer recommends holding soil at 65 to 80°F for germination. The one-flat Jump Start MT10006 uses 17 W, against 1,500 W for an air heater. For a full bench, the Bootstrap Farmer 60x21 in commercial mat (150 W) daisy-chains up to four mats.

Run mats through a thermostat so the soil doesn't cook: the Bootstrap Farmer mat controller handles up to 1,000 W but only goes down to 68°F, so it is for germination, not frost protection. Mats sit nicely on the benches in our greenhouse shelving guide.

How to choose a greenhouse heater

• Output vs heat loss. Run the formula above for your coldest typical night. If the answer is over about 5,000 BTU/h, one 120 V heater isn't enough.
• Power available. A 120 V outlet tops out around 1,500 W. More means 240 V or two separate circuits.
• Splash rating. IPX4 means protected against splashing water. The Palma, DR-218 and Palram HG1040 all list it.
• Thermostat. Digital is easier to trust; or add an external controller rated above the heater's amps.
• Fan mode. A heater with a fan-only setting doubles as summer circulation. For exhaust fans and vents, see our greenhouse ventilation guide.
• Backup. In real freezes, keep a second heat source: a propane unit for power cuts, or a second electric heater on another circuit.

Mistakes to avoid

• Sizing by floor area alone. A tall, single-wall house loses far more heat than its floor suggests.
• Putting a 1,500 W heater on a 10 A controller. The ITC-308's 10 A rating is below a 1,500 W heater's draw.
• Running propane in a sealed house. It adds moisture, carbon monoxide and ethylene. Vent it, every time.
• Trusting the dial. Read the temperature at plant height, not at the heater.
• Heating leaks. Gaps around doors and vents, and bare single-wall panels, cost more than any heater upgrade saves. Insulate before you buy a bigger heater, and make sure the house is anchored on a sealed greenhouse foundation.