Heater advice/recommendation
 

My fab Southern Burner heater has given up the ghost; no longer in business, parts unavailable, so I need a new backup heater in the greenhouse (Ohio, US) in case of main furnace failure or power outage. It must be around 25,000-30,000 BTU, work without electricity, ergo no fan. Needs to work from a standard thermostat connection or have its own thermostat, and come on automatically at the set temperature of ~55ºF. Any recommendations? The only thing I can find that looks like it might work is an unvented blu flame heater. Does anyone know if those are safe in an enclosed orchid greenhouse? There is a small 3" intake vent for the main heater, and currently an exhaust pipe from the Southern Burner which could be left as a fresh air vent as well if necessary. I would prefer a vented heater like the Southern Burner but can't seem to find one.

I have used an "unvented" propane heater in my greenhouses as backup for many years......BUT "unvented" is a misnomer. The key to using these successfully is to ensure adequate ventilation both for the flame to burn cleanly and then at a high level to allow combustion gases to expel. Get those right and you will be fine - compromise and get them wrong and your plants will suffer. The problem is that orchids take so long to show their displeasure that it will be a few weeks before you know success or failure. I have extremely unreliable power supply and have considered switching to propane permanently but we have only "unvented" heaters available here in the UK that I have discounted other than for temporary standby.

I have an identical problem. My second Southern Burner vented gas heater just went belly up. The pilot mechanism has always been unsatisfactory (very finicky) and a replacement vented gas burner with an electronic pilot would be preferable. I live in So. California so only need 30-40 nights/year of use. Did you ever find a replacement. Propane would be nice if it had a vented option