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Greenhouse Heating

Selecting Your Greenhouse

Heating Your Greenhouse


Greenhouse heating is an important issue to consider for your hobby or commercial greenhouse. The night temperature in a year-round greenhouse is the most important factor to determine which heating system is required. The greenhouse gardener also determines whether to winter over plants or to provide a constant growing environment.
Cool or frost free greenhouses maintain a night temperature of 40-45F (5-7C).This is suitable for frost sensitive plants and rooted cuttings
Warm greenhouse requires a night temperature of 55F (13C).Growlights are necessary for adequate light conditions in this environment.
Hothouse night temperatures are set at 65F (18C).This will provide a natural habitant 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. 
(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 mill plastic liner is fastened with a clip. Then, airspace is created between the plastic and the greenhouse covering.
  • 16mm 5 wall 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 triple wall polycarbonate and 8mm 4 wall polycarbonate.  It is approximately 80% more efficient than 6mm or 8mm twin wall polycarbonate.


  • 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.

Greenhouse Heater

  • 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.

Greenhouse Thermometer