The first decision to make when buying a greenhouse heater is the power source. Paraffin, butane and propane heaters are good options if your greenhouse doesn’t have mains power. Paraffin heats up quickly which is great for large spaces, but fuel can be costly. Propane and butane gas are typically more economical, but butane doesn’t reliably burn at temperatures below -2°C.
The best greenhouse heaters are electric; they don’t cause condensation like paraffin or gas and are easy to control.
Electric fan heaters work well in all sizes of greenhouse. Look for a fan heater with adjustable heat settings and/or a built-in thermostat. These offer more control over the temperature and electricity usage.
If your aim is simply to keep temperatures above 0°C, consider a low-power electric tubular heater. The purpose of these is to keep frost out. They have around 40 W of power and provide some warmth without hiking up your energy bill.
To keep a standard, small greenhouse (2.4 x 1.8 m) free from frost over winter, a 55 – 80 W heater will be sufficient. However, if you want to maintain a higher temperature, or heat a larger greenhouse, I recommend a more powerful 2 kW heater.
After comparing some of the best greenhouse heaters, the Bio Green Palma Greenhouse Heater is my top choice. It has a powerful 2 kW output that can effectively heat large greenhouses of up to 5.5 x 2.5 m (18 x 8 ft). It also has an external thermostat that can be positioned right next to plants, providing more accurate temperature readings to the heater.
Take a look at the reviews below for more information on this greenhouse heater, as well as some excellent alternative options.