Problems With Using Unvented Greenhouse Heaters
Wednesday, 19 December 2007 15:53
A frequently asked question (FAQ) is "Can I use unvented heaters in the greenhouse, either for back-up or as a primary heat source?
An unvented heater is one that is designed without a flue connection so that the heat and products of combustion are exhausted into the greenhouse. Dumping these flue gases into the greenhouse may improve the overall efficiency rating as compared to a conventional heater but the pollutants and added moisture from combustion may put your plants in jeopardy.
Unvented heaters can be fired with natural gas, propane or kerosene. These fuels are advertised as clean-burning. This is generally true if the burner is clean and has been adjusted to top efficiency. A heater that has been serviced in the fall will probably not be at peak efficiency as spring approaches. Inefficient combustion can emit unwanted and harmful pollutants into the greenhouse that can affect the plants and the people working with them.
Care should taken if you install unvented heaters. Be sure to have an adequate makeup air supply and provide frequent maintenance. Use indicator plants near heaters or commercially available indicator tubes to warn of excess levels of pollutants.
For more information about the fuels, the combustion process and their pollutants see the fact sheet:
Problems With Using Unvented Greenhouse Heaters
John Bartok, Extension Professor Emeritus, UConn
