Hi Valleyherb,
welcome to our little slice of Paradise here at the Orchid Forum!
I volunteer at the USF Botanical Garden here in Tampa Florida and their orchid greenhouse is heated exclusively with propane. I've never seen any problems caused by fumes so you should be fine. Friends that also use propane have to have some sort of 'jacket' on the tank when it gets really cold ( yes, that does happen in Tampa!) so do some research first about how to keep your tank from freezing!
