How to Heat & Cool a Greenhouse


Gardeners can use a greenhouse year round to produce fruits and vegetables at home. The greenhouse allows a gardener to control most of the aspects of the growing process such as soil composition, temperature and humidity and to centralize pest control. Greenhouses can also be made into a relaxing place to retreat to with a book or a drink. However, to enjoy those advantages the greenhouse needs adequate cooling during the summer and heating during the winter.

Step 1

Install vents on the top and bottom of the greenhouse. Installing a vent system can cool a greenhouse in most climates. Put a vent on the bottom as an air intake on both north and south sides to provide a good airflow inside the greenhouse and one on the top to allow for warm air to escape. You can also add a fan inside the greenhouse to be sure that the air circulates to avoid pockets of hot air that can damage your fruits and vegetables.

Step 2

Install an evaporating cooling system. On the east side of the wall make a hole so you can fit two fans with sufficient CFM: cubic feet per minute of air moved. To calculate how many CFM your greenhouse needs, use the formula height x length x width x 1.2. A 10 x 10 x 10 feet greenhouse needs 1,200 CFM power fans. Install the wet pads and the water system in front of the fans and seal the system for maximum efficiency. When running the system, open a vent to allow for hot air to escape. In hot climates, a simple vent might not be enough to keep the greenhouse cool. The most economical and efficient way to cool the greenhouse is to use an evaporating cooling system. This system is also works best in dry climates.

Step 3

Line the whole north wall with the 55-gallon metal drums, fill them with water and paint them black. Make sure the drums are exposed to the sun for most of the day. This system is not efficient enough to effectively heat a greenhouse and is usually used to maintain a greenhouse temperature above freezing. During the day the water captures energy from the sun and redistributes it at night. It might be all you need, even in a cold climate, when you are growing cold-resistant vegetables during the winter. Use that the following formula to determine how many drums you need. For an attached greenhouse, or a greenhouse with an isolated north side: Take the total area of south-facing glazing and multiply it by 2.5 to know how many gallons of water you need when you are in a cold climate, 2 when you are in a medium climate and 1 when you are in a warm climate. For a-free standing greenhouse, take the total area of south-facing glazing and multiply by 3 for cold climate, 2.5 for normal medium climates and 2 for warm climate.

Step 4

Install an active solar heating system. Use a solar collector to heat a tank of water and distribute the heat during the day and at night. An active solar heating system uses a large collector to heat a tank of water used at a heat storage source. Because the collectors are not limited in area like they are in a drum system, it is capable of producing more heat and can be used to heat a greenhouse.

Step 5

Install a wood stove to heat the greenhouse and maintain a constant temperature throughout the year. Installation of a wood stove must follow the same safety constraints as a stove in a house. A wood stove maintains higher temperatures than other methods and, by opening the foyer, is also capable of raising the carbon dioxide level in the greenhouse and promoting plant growth.

Tips and Warnings

  • When using a wood stove, always install a carbon monoxide detector visible from the outside as well as a carbon dioxide counter if you plan on using the wood stove to boost the carbon dioxide level in the greenhouse. Both gases are deadly, so take extreme precaution with both of them. When using a wood stove, use a fan system to circulate the air evenly inside the greenhouse and avoid stratification of colder air in certain parts of the greenhouse and warmer air in other places.

Things You'll Need

  • Wood stove and necessary pipes
  • 55-gallon metal drums
  • Solar collectors
  • Water tank
  • Wet pads
  • PVC evaporative cooling system
  • Fans


  • CFM Calculator
  • CFM per Sqf
  • Greenhouse Gardener's Companion; Shane Smith; 2000

Who Can Help

  • How to Calculate the Water Needed for a Passive System
Keywords: heating a greenhouse, cooling a greenhouse, greenhouse temperature control
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