Hello. First time poster here. We have a 20’ x 50’ tunnel with 6 mil double poly and inflation fan - it’s a Gothic style frame from Multi Shelter Solutions. We are in the market for a heat source for this currently unheated structure. I’ve been keeping an eye out for a second-hand propane furnace on kijiji, but all the models I’ve seen so far appear much larger than what we’d need for this size of tunnel. We are looking for a unit that is capable of adequately heating this structure to a temperature sufficient to propagate tomatoes and peppers. Any advice or recommendations regarding BTU output, sourcing a furnace, or heating a polytunnel in general are appreciated. Thank you.
You could try using a gas boiler and heating a network of pipes buried under it. It’s a pretty efficient solution as the ground acts as a heat sink. Your heat will be released gradually from the ground and keep the root zone nice and toasty. However you’ll need to insulate the perimeter of the tunnel underground to not lose the heat to the outside of the tunnel.
I’ve worked in plenty of greenhouses with old furnaces (gas and oil) and they tend to be rather bulky in general. I would be careful with buying a furnace that is bigger (in BTU, not in size) than you need as that will decrease its fuel efficiency and shorten its lifespan because of the frequent short-cycling.
MSS should be able to help you determine the right size furnace and BTU’s needed for your tunnel. Or check this link for a quick and easy BTU calculator:
We also have a 20 x 50 double poly tunnel from Multi Shelter. It’s outfitted with a propane furnace so we can heat it for seedling production. I believe the output of the heater is 116,000 BTU. To be honest I’m not sure if that’s overkill. That’s just what they sold us when we went to our propane provider (probably should have done more research beforehand). I do know that it works really well. The major downside of propane heat is that it’s very expensive, and we learned very quickly that it doesn’t take long to go through a lot of propane.
To cut down on heating costs this season we are using a germination chamber to get seeds started. And we just built a table with bottom heat that we’ll use to keep our hot crops at a constant temperature without having to keep the whole house heated to a high temp.
Hope that helps! Feel free to email me if you have more questions email@example.com