According to the Alabama Extension Service, greenhouses are poorly insulated structures. The thin covering of a greenhouse that lets light and heat in during the day also lets heat out at night. Although a greenhouse can create a warm climate for tender plants during the day, at night those tender plants can freeze if you don't add a heating source to keep them warm. Heating systems can cost thousands, but you can add heat to your greenhouse inexpensively by composting wood chips directly in the greenhouse.
Wrap the chicken wire into a circular cage and crimp the ends. Your chicken wire circle should be at least 3 feet wide by 3 feet tall to effectively create hot compost. Larger compost piles will hold heat for a longer period.
Place the chicken wire circle in the center of your greenhouse.
Fill your chicken wire cage with 2/3 wood chips and 1/3 manure.
Wrap the cage with semi-flexible plastic tubing. Hook one end of the tubing to a water pump. The other end of the tubing should run from the compost pile around the greenhouse to distribute heat evenly.
Wrap the compost pile and the semi-flexible plastic tubing with black plastic.
Water the compost so that it is as wet as a wrung-out sponge. Test the compost daily with a thermometer to ensure that it stays between 120 and 160 degrees Fahrenheit. Turn the compost pile inside-out any time the temperature drops below 120 degrees. The compost will heat the water. To heat the greenhouse, pump the hot water from the compost pile through the greenhouse.