Maybe it would help quantify the replies if you gave some more details....size of glass-house, and main genera grown.

This post was edited by arthurm on Tue, Dec 10, 13 at 21:00

I'm located in Greenville, SC/ zone 8. My greenhouse is wood framed and measures 12 ft x 12 ft. The covering is solexx, which is then covered with a clear pool cover for extra insulation. I'm growing an assortment of orchids (Vanda, Cattleya, Phalaenopsis, Dendrobium, Miltassia, Brassia) and Bromelaids (Neoregelia, Vriesea, Aechmea). I'm currently heating with an oil-filled radiator type heater w/ two strands of C9 Christmas lights weaving underneath the benches. I only turn the lights on to give supplemental heat when outside temps dip into the low 20's or lower.

I guess my main concern regarding the portable propane heater is the ethylene gas/ carbon monoxide. If I was to use the propane heater, it would only be for a short time (3-8 hours) during a power outage or an unusually cold night. Would this short amount of time be harmful to the plants? I can deal with bud blast and wilted flowers, but would hate for the propane to prove fatal to the plants.

This post was edited by DwayneSC on Wed, Dec 11, 13 at 5:13