Greenhouses are wonderful places to grow plants during the cooler months of the year. They trap daytime solar energy to produce temperatures inside that are much warmer than the outside. However, if your temperature falls below freezing at night, you should provide supplemental heat in your greenhouse. The size of heater needed will depend on the size and insulation factor of your greenhouse. Using a utility heater in a greenhouse is a breeze and will keep your plants from succumbing to the cold.
Calculate the size of heater needed for your greenhouse. See resources for a greenhouse heater size calculator that will calculate the British Thermal Units (BTU) needed, depending on the area and insulation value of your greenhouse.
Convert BTU to watts since most electric utility heaters are sized using watts. See resources for a great online converter.
Purchase the correct size heater and place in your greenhouse. Read its operation manual and maintain all necessary clearances to prevent starting a fire.
Plug the heater into an electrical outlet that is appropriately sized for the heater. If no such outlet exists, you should hire a licensed electrician to run power to your greenhouse.
Set the thermostat on the heater to your desired setting. Turn the heater on.
Place a thermostat in your greenhouse that is not in direct sunlight and also is not near the heater. Keep an eye on this thermostat to ensure the heater is heating your greenhouse to your desired temperature. If a discrepancy exists, adjust the thermostat on your utility heater appropriately.
Place a few fans around your greenhouse to increase air circulation. This will distribute the heat evenly around the greenhouse and prevent hot and cold spots.