Knowing how to heat a greenhouse helps you maintain the perfect climate for your plants throughout the year. While the greenhouse's desired temperature range depends on the types of plants, most plants with foliage need to stay between 65°F and 80°F.
So, most greenhouses that are used for overwintering require some type of heat, and this can be provided by the sun or by the earth, in the form of geothermal heating. Electricity, kerosene, and natural gas are other sources of heat for greenhouses.
Passive Solar Heating
Passive solar heating is the very idea behind greenhouses: Light from the sun shines through transparent panels to create interior heat. Maximize the passive solar heating effect by keeping the panels clean and by adding insulation
Effective only during day
Affected by poor weather
Solar heating for greenhouses uses photovoltaic (PV) solar panels to collect the sun's energy and convert it to electricity, which is then stored in batteries. The electricity can be used to power a dedicated greenhouse heater or fan or any type of heater that runs off of electricity.
High initial cost
Best for sunnier areas
With a geothermal heated greenhouse, tubes are buried six to 12 feet below the ground in a loop that brings the tops of the tubes into the greenhouse. The tubes are filled with either air or a fluid like propylene glycol or methyl alcohol. Air-filled heating systems can even work in reverse. In summer, they draw colder air from the earth to cool down the greenhouse.
Free heat generation
High upfront cost
Forced Air Heating
Forced air heaters heat up electric coils and blow the heated air throughout the greenhouse. Heaters can be powered by 120V household current or by solar panels. Forced air heaters quickly get warm air moving during sudden cold spikes.
Quickly generate heat
Backup heat source
Infrared heaters use infrared (IR) radiative sources, instead of forced hot air, to transmit heat to the physical objects in the greenhouse. Rather than heating up and blowing air, IR greenhouse heaters heat the plants, the greenhouse frame, and objects like tables.
IR greenhouse heating can save between 45- and 50-percent on energy over other sources. Stick with low-intensity IR lamps as lamps that reach the far end of the red spectrum can harm the plants.
Doesn't dry air
Air feels cold
May damage plants
Oil-filled portable radiators often used in the home can also be used to maintain an even temperature range in the greenhouse. Powered by 120V electricity installed in the greenhouse or via a cord from the home, oil-filled radiant heaters heat up slowly but stay warm longer because the oil absorbs heat and continues to radiate it.
Easy to set up
Portable kerosene heaters use liquid kerosene to create quick heat in greenhouses in cold snaps or for emergency use. Kerosene heaters used in greenhouses must be vented. Methods other than kerosene are generally preferred for heating greenhouses.
Electricity not required
May damage plants
Heaters powered by natural gas can be used to provide on-demand heat for greenhouses. Heating units are usually suspended near the ceiling so that they can be vented. A low-pressure gas line must be brought over from the home through trenches.
Lower cost power
Buried gas line required
Requires professional installation
Tips for Heating a Greenhouse
- Black plastic jugs filled with water, bricks, or other thermal mass storage devices will continue to radiate heat throughout the night.
- Add a compost pile inside the greenhouse to generate heat.
- Build a greenhouse with the lower half embedded in the ground to take advantage of the earth's temperature-regulating qualities.
What is the best source of heat for a greenhouse?
The sun is the best source of heat for greenhouses as it is free. Store built-up daytime heat in thermal mass devices like water jugs or bricks. The devices radiate heat as the temperatures cool.
What is the easiest way to heat a greenhouse?
The easiest way to heat a greenhouse artificially is with portable forced-air or oil-filled radiant heaters, using household electricity.
How do you insulate a greenhouse?
You can insulate a greenhouse quickly by taping up bubble wrap on the side walls of the greenhouse. For a longer-term solution, consider installing thermal insulated polycarbonate panels.
Growing Indoor Plants With Success. University of Georgia Extension
Geothermal Heat for Greenhouses. eXtension Farm Energy
A. Kavga, T. Panidis, V. Bontozoglou, S. Pantelakis. Infrared Heating of Greenhouses Revisited: An Experimental and Modeling Study, November 2009. Transactions of the ASABE (American Society of Agricultural and Biological Engineers) 52(6)
Unvented Kerosene Heaters - OK for Greenhouses? New York State Flower Industries Bulletin No. 149. February. 1983