How To Heat A Greenhouse for Free

Wondering how to heat a greenhouse for free? We list the cheapest way to heat a greenhouse in winter and keep temperatures steady.

Reader Contribution by Lindsey Schiller
Updated on July 20, 2023
article image
by AdobeStock/Rechitan Sorin

Wondering how to heat a greenhouse for free? We list the cheapest way to heat a greenhouse in winter and keep temperatures steady.

Greenhouses can be interesting environments to grow in. This is because standard greenhouse materials like glass and plastic (“glazing”) are extremely good at letting in light and heat in, and extremely good at letting heat out. With so much glazed surface area, greenhouses usually overheat during the day if uncontrolled. And because glass and plastic provide no insulation, at night they lose all that heat, causing them to freeze. Take this October day in Boulder, Colorado for instance: An all-glass greenhouse fluctuated from a high of 110 F to a low of 30 F in one day. Plants, like people, do not like this.

The primary challenge with greenhouse growing is stabilizing these temperature swings. Conventionally, people do this by blasting energy via heating or cooling systems into the greenhouse. But the smarter, more sustainable way of creating a stable greenhouse environment is to harness the excess solar energy coming in during the day, store it and use it at night. Or, if working with an existing greenhouse, to add an efficient heater that uses cheap and renewable fuels. These strategies all take understanding and research, and have some upfront cost, but the pay-back in terms of added growing and long-term savings is well worth it.

Also, remember there’s no cheaper energy than the energy you don’t have to use, so if designing a new greenhouse, build it so that it does not require much heating and cooling in the first place. This means using building an air-tight, insulated structure, using proper roofing materials, and orienting the greenhouse with the glazing facing South — where all our light in the Northern hemisphere comes from. If growing in an existing greenhouse, you can insulate your greenhouse and weather-strip air leaks among other things. Reducing your energy requirements to a minimum is always the first step, then incorporate the strategies below.

Store solar energy in thermal mass

The easiest and most common way to even out the temperature of your greenhouse is utilize thermal mass, also called a heat sink.  Thermal mass is any material that stores thermal energy. Most materials do this to some extent, but some do it much better than others. Water for instance, holds about 2 times as much heat as concrete, and about 4 times as much as soil.

Comments (0) Join others in the discussion!
    Online Store Logo
    Need Help? Call 1-800-234-3368