Greenhouses provide excellent spaces to extend your growing season. They are very useful in northern climates where frosts happen late and come early. By harnessing the sun's solar energy, it can be several degrees warmer inside the greenhouse than outside during the daytime hours. However, at night you may still need supplemental heating. Without it, the greenhouse will drop down to the outside temperature during the night. If this is below freezing, it can be damaging to your plants.
Calculate the BTU (British Thermal Units) needed to heat your greenhouse. Look at the greenhouse heater size calculator in the resources to calculate this. It needs the area of your structure, your minimum outside temperature, your desired inside temperature of the greenhouse and the insulation value of your greenhouse.
Convert BTU to watts since most electric heaters are sized in watts. See the calculator in resources for an easy conversion tool.
Verify that you have a large enough power source in your greenhouse to run the heater. Iif you have a small home greenhouse and require a little heater you can usually run an extension cord to the greenhouse from a nearby power source.
Purchase the electric heater and set it up in your greenhouse. Keep it the recommended distance from any objects in the greenhouse. Combustible objects placed too close to the heater may catch fire.
Plug the heater in and set the thermostat on the heater to your desired temperature. It will cycle on and off to maintain the temperature.
Place a thermometer on the other side of the greenhouse in a sheltered spot to keep an eye on the temperature. Adjust the thermostat on the heater as necessary to make up for any temperature discrepancy.
Place a box fan or two in the greenhouse. This will circulate the heat efficiently and keep your plants healthier.