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Are there any problems with uuing propane heaters in a greenhouse? We may have temperatures in the upper teens next weekend and I don't think my electric heater alone will keep the temperatures above freezing. I mostly have species that can tolerate freezing temperatures but I am concerned about the many seedlings less than one year old. I have heard open flame gas heating can release fumes that are toxic for plants but I'm talking about propane heaters that have heating elements.

Just remember you need oxygen for the heater to burn and an exhaust for the combustion gases. You don't want to kill off the plants.

mikethecactusguy wrote: ↑Thu Feb 11, 2021 12:57 am Just remember you need oxygen for the heater to burn and an exhaust for the combustion gases. You don't want to kill off the plants.

Or yourself

Perhaps the worst thing for a succulent greenhouse is the huge amount of water vapour produced (C3H8 + 5O2 → 3CO2 + 4H20). You will get loads of condensation and humidity and your plants will suffer. The element does not change the combustion products produced.

You also get reduced oxygen and too much CO2. If the burn mixture is not correct you may get some nasty gases given off. Like carbon monoxide.

A bit of ventilation is not really enough for gas. A chimney and an air intake like an air brick in a house might do. I would just get another electric heater.

Can you upgrade the insulation?

Thanks for the replies. I have added more insulation and covérings for the less cold-tolerant species. I have decided to bring most of the seedlings into my house. The latest forecast low for Monday night is 10F so I'd rather not take any chances.