Here is my latest question: Vented vs. non-vented heater? I seem to recall that Marni has at least one non-vented but I wonder if the size of the gh is the key to wheter one can get away with no vent? With mine being much smaller, I wonder if I should go with vented. I talked to the guy at Southern Burner and he said that 80% of his orchid greenhouse users buy the vented type. He said that their vented ones are ~80% efficient and have a capacity of 25,000 btu. The non-vented are over 90% efficient (99%?) and have a capacity of 20,000 btu. Vented is an extra hundred bucks and would require some hassles to frame in an opening in the roof and to obtain the vent pipe, flashing, etc. I believe he mentioned ethylene gas as a potential issue with the non-vented and that it can cause bud blast. I'm curious if there are other gasses that might be a concern. But I'm also thinking that the vast majority of my plants won't be blooming during the winter anyway so bud blast may not be an issue. The source will be natural gas and with that level of efficiency maybe other gasses aren't really a concern? As always, any input is appreciated.