The Orchid Source - Orchid Forum

I've begun installing unvented gas heaters in my 1000 sq ft greenhouse. I have had 5 Southern Burner vented heaters supplying heat for several years. These have reapeatedly been problematic, with pilot flames going out for unknown reasons or malfunctioning so that they do not power the thermocouple to the thermostat, they also require annual cleaning. They are only 80% efficient.

I have recently installed two 30,000 btu unvented propane heaters, purchased from Northern Tool, the type used in homes. These are 99% efficient. I have a fresh air source near the burner of each heater and the greenhouse is not too tightly sealed...allowing a steady source inflow of fresh air. I have seen no damage to flowers or plants from the exhaust in the greenhouse and its been nearly three months.

Most of the exhaust from gas heaters consists of water and carbon dioxide, both of which are in high demand by the plants. The danger to plants would be if small amounts of the propane fuel is going un-burned by a poorly maintained burner...small amounts of natural gas fuel does not have this effect on plants. A danger to humans would be using a large heater in a small, confined space without a fresh air source which might produce carbon monoxide.

I will probably remove these unvented heaters during warm weather since they are not built to withstand lots of moisture and corrosive fertilizer salts. But, they are lightweight and easy to move.

Ed, if you don't already have one, you could get yourself a carbon monoxide detector.

Yes, thanks, I have one. The carbon monoxide is produced when there is insufficient oxygen to burn the fuel. I don't have that problem.

Hi Group! I used this type of heater for more than 30 years without any problems. It is important to keep the burner's mixer clean, so that the flame remains blue (so that no yellow feathers to the flames are seen). These heaters are very efficient and they do provide CO2 which the orchids need, and, they eliminate the need for a CO2 generator.