Heating and Cooling a Solar Greenhouse
Probably your main concern about buying a greenhouse isn’t so much the cost but how do we heat it and what will it cost. Greenhouses require heat only after the sun sets. A 1500 watt space heater is a good starting unit; it should have a fan to circulate the Heat. Propane or electric units are fine. A garden with very fragile plants or one that has very few plants will require a larger unit.
Solar mass is anything inside a greenhouse that will pick up heat during the day and give it up at night. On of the best sources of solar heat is a 55 gallon drum filled with water, paint it black and it will cut heating costs. It will not be hot to the touch but it will be warm during the day and give heat off at night.
We recommend a 4” layer of sawdust on the ground inside the greenhouse; moist sawdust forms an excellent barrier against cold. Since the Solar Prism Greenhouse does not require a foundation, the earth holds heat as well.
Compost rigs are a natural for your greenhouse, shred leaves and clippings, turn the pile as often as possible and add a commercial compost mix to help it work faster. Compost temperatures can reach over 125 degrees.
Weather stripping can be done to the windows, doors, and vents. Use caution around the vents as they close fairly tight without the stripping and could jam.
Generally, the gardeners who have the lowest heating cost are the ones who make the most of their greenhouses – less air mass to heat.
If you’re new to green housing, you will probably try to maintain temperatures that aren’t realistic. After some experimenting, chances are that you will find that your plants do very well through frosts and cold nights. They are in warm soil and without cold winds blowing over them, can handle most cold snaps. Try to resist checking your thermometers when it is cold and windy, that blast of cold air that hits your plants when you open the door accounts for quite a few causalities.
We know of gardeners who have wood stoves and oil stoves that they have put in their greenhouses, but only after working out venting the fumes and smoke.
Cooling is much easier. The roof vents in our design open in opposite directions and the windows open on each end. This generally will catch any breeze. Most gardeners have a fan for their comfort. The misting system will aid in heat control also. You can place your greenhouse so that it will be in the shade during the summer.