Not every heater belongs in a greenhouse. The combination of high humidity, organic material, and limited ventilation creates a unique environment where safety, moisture tolerance, and precise temperature control matter more than raw power. Here’s how to navigate the options. For broader context on greenhouse heating strategy, see our Climate Control guide.
Purpose-built for greenhouses rather than adapted from a household space heater. The IPX4 splash-proof rating means it’s designed to handle the humid greenhouse environment. The digital thermostat provides precise temperature control, and the lightweight design makes it easy to reposition. Our top overall pick for hobby greenhouses.
Infrared heating warms surfaces and plants directly rather than heating the air first, which means less humidity disruption. The stainless steel housing resists corrosion in humid environments. The detachable thermostat can be mounted at eye level for convenient reading. A reliable, well-reviewed workhorse.
The heavy hitter for large or off-grid greenhouses. The adjustable BTU range lets you dial in heat precisely. Must be used with adequate ventilation—propane combustion produces CO and moisture. The ODS safety system shuts down the heater if oxygen levels drop. Best for growers who need serious heating capacity without electrical infrastructure.
If you have a large greenhouse and 240V power available, the CZ220 delivers serious heat without taking up any floor space. Adjustable louvers direct airflow where you need it. Professional installation required for the hardwire connection. Overkill for small hobby greenhouses, but perfectly sized for 10×16+ structures.
Not a room heater—a soil heater. Seedling heat mats raise soil temperature to the 65–75°F range that warm-season seeds need for reliable germination. The thermostat combo prevents overheating and gives you set-and-forget temperature control. Essential kit for anyone starting seeds in a cool greenhouse.
A workhorse convection heater that provides strong radiant and convective heat over a wide area. The 360-degree heat output from the convection dome distributes warmth evenly. Long runtime on a standard 20 lb tank makes it cost-effective for extended cold snaps. Requires ventilation for combustion gases.
The formula for estimating heating needs:
Required BTU/hr = Surface Area (sq ft) × Temperature Rise (°F) × Heat Loss Factor
Heat loss factors by glazing type:
| Glazing Type | Heat Loss Factor (BTU/hr/sq ft/°F) |
|---|---|
| Single glass or poly film | 1.0–1.2 |
| Double-pane glass | 0.6–0.7 |
| Twin-wall polycarbonate (4–6mm) | 0.6–0.7 |
| Multi-wall polycarbonate (8mm+) | 0.4–0.5 |
| Double-layer inflated poly | 0.5–0.6 |
Example: An 8×12-foot twin-wall polycarbonate greenhouse (total surface area including roof and walls ≈ 400 sq ft), maintaining 50°F inside when it’s 20°F outside (30°F rise), with a heat loss factor of 0.65:
400 × 30 × 0.65 = 7,800 BTU/hr needed
A 1,500W electric heater produces about 5,120 BTU/hr, so you’d need something stronger—either a 240V electric unit or a propane heater in the 10,000+ BTU range.