Worse come to worst, drag your gas grill into the GH and crank her up. It may not have the BTUs to keep it toasty, but it won't let it freeze.
After one heater failure, and one missed propane delivery, I purchased a propane "radiant heater" and a couple of extra tanks.
Is it better to use propane or kerosene as a back up heat source?
---------- Post added at 07:40 PM ---------- Previous post was at 07:34 PM ----------
I went all last winter without an alarm, but I don't want to go through that again. It's just not worth loosing everything and I only had about 50 orchids last winter.
I have had this in my 3 greenhouses for a few months now... Works great. I have it call my cell when one of the alerts I set trips. Woke me up when GH#1 got to cold because I didn't get the fitting on the spare lp tank tight and the pilot when out when the system switched bottles. Paid for itself right there.