Propane Heating

[Bradfo69]

Doesn't appear as though many people visit this forum but I'll ask anyway. As you may have read, I'm a new greenhouse owner and working on setting it up. I'm making my considerations for heat. It's set up already with a 240v electric heater. I'm considering switching to propane.

It's a small 8 x 15 Sunglo and I'm guessing I need about 13,750 btu's. I'm finding most un-vented heaters are less expensive than vented but I know you need to be careful using un-vented with orchids. A manufacturer rep (who is familiar with greenhouses) claims the main issue is putting out excessive CO2 and water. The water vapor of course, causes condensation issues on the walls and the co2, while good for the plants, is excessive at night (when the heater is most frequently run) while the plants should be resting. I also understand the issue is ethylene gas but I've heard people used un-vented anyway. Same with kerosene, natural gas etc. What are peoples experiences? I'm thinking about something like a Comfort Glo blue flame heater.