Heating greenhouse in zone 4

I know heating has been discussed quite a bit but I can't find all the information. I have a 12x24 poly film greenhouse. I would like to start it up in March. Any ideas for heating? I don't have electricity out there. How do propane heaters work? Cost? Cost of propane for two months? Dangerous? Thanks for any advice.

If you haven't went through a winter before with a greenhouse, be sure you have a very reliable heat source. It almost seems to be colder inside than out.
The plastic doesn't hold heat very long, so if you heat quits you have very little time to correct it.
Get a remote thermometer, so you can know the temp without making a trip out to the greenhouse. They are reasonable.
As for heat source, I would figure a way to get electric out there. If it's not to far, a heavy cord would work. (I bought a 14-3, 100 foot one from Menadrs for under $30.00 for our construction business.)
Here we use fuel oil for heat. We now have regular greenhouse furnaces, but started out with used house furnaces. We still have one in our wood shop.
You do not have to worry about fumes killing plants.
Be sure & use #1 fuel, as others will get to thick in cold weather. It only costs a few ¢ a gallon more.
We find the furnaces by running a wanted ad in a local shopper. The last time I ran one, I got about 20 reponses.
You should be able to pick one up for $100.00 or less. Don't grab the first one you see, there might be a better one at the next call.
Usually they will want you to take the barrel too. They are normally 265 gallons. That is large enough so you can get a farm Co-op to deliver the fuel.
Good luck, E-mail me if you need more info.
Bernie

I have a lean-to that's heated by the house boiler, and a polycarb free-standing unit that I'm going to heat with a "milk house" electric heater. I have a back-up propane heater on order from IGC (you can check them out on-line) for the inevitable power failure.

The lean-to is heated to 60 degrees maximum (for orchids and tropicals), and the free-standing will be heated to a maximum of 40-45. The free-standing polycarb has 4mm walls, and I'm praying the electric bill won't bankrupct me.

- Kathleen (Zone 6, NW Rhode Island)

Kathleen, how cold does it get there? Here we can expect some nights to go done to -30º or lower. A milkhouse heater would only chew up kilowatts, not keep anything from freezing. We can expect below freezing temps every night, starting in a few weeks. A lot daytime temps will never rise above 32º either.
That is the reason we don't even think about heating a greenhouse over winter.
We start about min February. Then we only heat a small house & open a new one as we need room.
Bernie

I'm 2 Zones warmer than you -- we get nights in the teens and a couple of real killers that get down to minus numbers, but on average I'd say that the night temperatures are in the 20s. We have the usual January thaw when the nights are in the 50s or even 60s, but it's awful from late January to early March.

I'm hoping and praying that keeping the Rion GH at 40-45 degrees won't bankrupt us. If we have a really bad night (or a power outage), I have a small propane heater. I wanted to get a regular propane heater for full-time use, but my DH didn't think the electric heat (to keep the gh no warmer than 45) was the way to go. I wonder now if he considered the fact that we have DAYS that are in the single numbers and NO SUN?

- Kathleen (Zone 6 - NW Rhode Island)