Unpainted jugs or barrels will still hold heat, but a black surface can absorb enough sunlight to radiate up to 300 BTUs per 1 sq ft (930 cm2). [2] X Trustworthy Source University of Georgia Cooperative Extension Division of the University of Georgia focused on research and community education Go to source To be fair, it’s true that jugs or even barrels of water aren’t going to keep your greenhouse toasty warm on a cold night, especially after a cloudy day. But they may provide enough radiant heat to keep your plants above freezing, possibly in tandem with one or more heating methods.
Line the floor of your greenhouse with bricks or pavers. Place rocks or bricks around the bases of your plants. Stack up a “hot wall” of concrete blocks and paint them black. Like with the water barrel wall, set it up where it will absorb the most sunlight that has already passed through the greenhouse.
On a cold but sunny day (when the inside temperature of your greenhouse is much warmer than outside), walk around inside the greenhouse and use your hands to feel for cold drafts. Repair or patch up these areas to limit unnecessary heat loss. Weather sealing might only make a slight temperature difference. But, if it keeps your greenhouse at 35 °F (2 °C) instead of 32 °F (0 °C) on a chilly night, those few degrees might make all the difference!
This is a good option if your greenhouse gets lots of sunlight during the colder months. If you get minimal sunlight during the winter, however, it’s best to let in as much of the light as possible.
To figure out how much fan power you need, double the floor area of your greenhouse and compare this to the cfm (cubic feet per minute) rating of the fan. For instance, say your greenhouse is 6 ft × 8 ft (1. 8 m × 2. 4 m): 6x8=48; 48x2=96; so, use 2 fans that are rated for 50 cfm each (50x2=100). To convert cfm to m^3/h (cubic meters per hour), multiply by 1. 7.
Stir the mixture and add more water every few days, and add more compostables in the same ratio as needed. The interior of a “hot composting” pile can reach 155 °F (68 °C) within a couple of days. This isn’t the most fragrant way to add warmth to your greenhouse, but it works!
“Hot bed” composting is also less odoriferous than “hot composting. ” But this doesn’t need to be an either/or proposition—instead, try using both methods in your greenhouse.
Remove the covers in the morning so the plants get better air circulation. Also, especially on sunny days, the plants may overheat if you keep them covered.
Animals also breathe out carbon dioxide, which your plants will in turn “breathe” in. You don’t have to keep your animals cooped up inside the greenhouse all the time. Give them some time and space to roam during the day, for instance, then move them to the greenhouse at night. Don’t let animals just roam freely in your greenhouse—they’ll turn your plants into snacks!
Choose an electric heater that is designed for the size of your greenhouse. Use a thermostat so the heater doesn’t run unnecessarily. Keeping a greenhouse at a minimum of 45–50 °F (7–10 °C) is preferable, but going as low as 37 °F (3 °C) is okay if you have fans circulating the air. [13] X Trustworthy Source Royal Horticultural Society Leading gardening charity in the U. K. providing resources for identifying, growing and caring for flowers and other plants Go to source Do detailed heat loss calculations for precise information on your heating needs and efficiency. For more info, check out University of Georgia Extension’s publication on this topic.
It’s easier—and likely less expensive—to install a geothermal system while building your greenhouse, as opposed to adding one after the fact. For more on this topic, check out the following: https://ag. umass. edu/greenhouse-floriculture/fact-sheets/geothermal-heat-for-greenhouses https://www. ourendangeredworld. com/eco/geothermal-greenhouse/ For an example of a geothermal installer, check out the following: https://ceresgs. com/environmental-controls/gaht/
