Emergency: using unvented propane in greenhouse - help!

9 years ago

Hey everyone,

I'm hoping someone with some experience using an unvented heater can offer some advice. Here's our situation:

We've spent the past couple of months moving onto a new farm, and have been installing infrastructure. We've built two gothic-style greenhouses; each is 30' x 48'. The greenhouses are full constructed and ready to use, and they're supplied with propane. Each has a standard, large, vented greenhouse heater.

However, the electric company hasn't been able to put us on their installation schedule until the end of February. This means that we won't have any electricity in the greenhouses for another month. But, we need to start the first of our transplants next week, and then we'll be starting all of our tomatoes the first week of February, amongst other things...so in other words, we'll need to have transplants in one of the greenhouses for about a month before we've got any electricity to run the blower motor that inflates the double plastic, or--more importantly--the electrical component of our big propane heaters.

So, we've been trying to come up with some kind of temporary solution to get us through the next month. We have a generator, but the cost to run it 24/7 (so that the heaters can kick on whenever they need to, and so that the fans for the inflated plastic can run) is exorbitant.

My first thought was to build a very small, simple, caterpillar-style hoop house--something like 8' wide x 16' long x 7' high (in the center)--and put a portable, unvented propane heater in there with a thermostat for the seedlings. The idea with the unvented, portable heater is that it wouldn't require electricity. I've used a calculator and determined that based on our zone, our desire to keep the hoop house at a minimum of 60 degrees at night, and the surface area of an 8x16 tunnel, we'd need roughly a 25,000 BTU heater.

I also thought it might be possible to somehow section off part of one of our greenhouses (so that there's a smaller space to heat), and use a similar type of heater.

My biggest concern is carbon monoxide buildup from the heater. I haven't been able to find a definitive answer about this online, so I figured the most sensible thing to do is ask other growers who've been in a similar situation. I have two sets of questions, basically:

1) Does it make more sense to build a small caterpillar-style hoop house, or to try to section off part of one of our greenhouses? We have the materials on hand for the caterpillar tunnel, so we wouldn't be buying anything.

2) Will we be alright running this kind of heater without ventilation? I doubt that the hoop house would be airtight, but I'm not sure if minor air leakage would serve as adequate ventilation. Does anyone recommend a particular heater if so?

Thank you in advance to anyone who can help. We're really in a bind here, and I appreciate any input from anyone.

Comments (4)

henhousefarms
9 years ago
When we built the greenhouse years ago we put in an unvented propane heater. There was plenty of ventilation to keep running. However, the transplants started getting white spots in them and generally looked sickly. Ventless heaters put out a lot of water vapor which condensed on the ceiling and with all the CO2 it also put out was producing "acid rain" that dripped down onto the plants and bleached them. Switched to a vented heater and problem solved. I do not think the vented heater required power but it's been a while since I messed with it (it's up at the north farm). I suppose for a real short term until you get the power hooked up you would be OK but as a long term solution it is poor.

Tom
derock_gw
9 years ago
How far are your greenhouses from your power source?
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barrie2m_(6a, central PA)
9 years ago
At the Mid-Atlantic Veg. Conference Judson Reid, Cornell, gave a horror story about a grower using a portable propane heater. We all use them as backup but you need to be careful. My take on your situation is that you'll need lots more BTU output for Feb and early Mar., possibly 10X as much.

Consider setting up a tunnel within your greenhouse and even using additional row cover over plants for the cold nights. I no longer do that since I now use inside wood stoves, but you need to be careful even using them. Are there any chances that you could keep plants under shop lights within your heated house,etc. until the end of Feb.? When starting flats of tomatoes you really only need limited space for the first 3-4 weeks.
grnnygrn
9 years ago
I use a ten by twelve hoophouse within my 30 by 72. It works great. Is very easy to heat. I use a small propane heater. I'm zone 3. One of the things you will find is that the small house will stay about 10 degrees warmer than the big one at night without any heat. And more importantly, the small one can go up to 110 degrees on a sunny day. Make sure you remember to open it for ventilation on sunny days.