Greenhouse Heating Options
It is important to consider heating your greenhouse. The night temperature in a year-round greenhouse is the most important factor to determine the heating system that will be best suited for your needs. The greenhouse gardener must also decide to over winter plants or to provide a constant growing environment year round.
Cool or frost free greenhouses maintain a night temperature of 40-45ºF (5-7ºC). This is suitable for frost sensitive plants and rooted cuttings.
Warm greenhouses require a night temperature of 55ºF (13ºC). Grow lights will be necessary to allow for adequate light conditions.
Hothouse night temperatures are set at 65ºF (18ºC). This will provide a natural habitat for tropicals and exotic plants.
To calculate your greenhouse heating requirements: calculate the wall and roof space of your greenhouse by:
(multiply the width of the greenhouse times the length of the greenhouse) x (the difference between coldest outdoor winter temperature and the desired night temperature) x 1.1
This will provide you with the number of BTU’s required to heat your greenhouse. For example, your greenhouse is 8 x 12. The coldest outdoor temperature is 0 degrees F. You want to keep the greenhouse at 65 degrees F at night. If you are not sure how to do the calculations, please call us at 1-800-665-2124.
(8 x 12) x (65 – 0) x 1.1 = 6,864 BTU’s
- Warm greenhouses can be twice the cost of a cool greenhouse.
- Insulating the greenhouse can reduce the heating cost by 30% or more. To the inside of the greenhouse frame, a clear 4 mil plastic liner can be fastened with a clip. Then, airspace is created between the plastic and the greenhouse covering.
- 16mm fivewall polycarbonate is the most energy efficient glazing material available in today’s greenhouse market. With an R value of 3.03, it is 50% more efficient than insulated double glass, 10mm triplewall polycarbonate and 8mm fourwall polycarbonate. It is approximately 80% more efficient than 6mm or 8mm twinwall polycarbonate.
Greenhouse Heating Units
- Heating requirements depend on the size of the greenhouse, the night temperature required and the expected outside low temperature.
- Electric heaters are the most common source of heat for a small greenhouse. You can also consider using natural gas or propane.
- The greenhouse gardener becomes very dependent on a maximum-minimum thermometer. This thermometer records the daytime high temperature and the overnight low temperature.
- The thermometer readings will determine whether to adjust the heating thermostat. It’s always a good idea to keep a journal as a reference tool from year to year.