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secondspring

Emergency: using unvented propane in greenhouse - help!

secondspring
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're fresh market growers, and farming is our full-time job. 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 (6)

  • martini100_gw
    9 years ago

    I have a 12 x 20 x 8 hoop house that we put up this past summer. I have been growing basil. We have (2), unvented Mr. Heater Big Buddy propane heaters hooked up to 20# propane tanks inside. (Maximum BTU's 18,000 per heater on high, minimum on low 4,000 BTU's.) They have kept my greenhouse in the 60's at night when both on low. Running only one on medium (9,000 BTU's) when lows are mid 20's to 30's keeps it in high 50's, low 60's. During "polar vortex" weather both are running on medium. I also have a small electric heater that kicks on if one of the heaters would go off at night.

    The only "venting" I have is due to the house not being tight like a drum. I do open door windows to vent during sunny days and open periodically in evening to let fresh air in. I also have a carbon monoxide monitor inside just for safety. I have not had a problem with temperatures.

    The heaters do, however, kick a lot of moisture into the air so make sure the condensation will drain off to the bottom of the house and not sit on the ceiling. I did not account for that so I have a dehumidifier running which has helped.

    Good luck!
    Lisa

  • dbarron
    9 years ago

    This is in the nature of urban legends (but not quite). There's an unvented propane heater system that my father used to heat his house and every year when he started heating, my houseplants would nose dive....badly.

    I moved out this November, and my plants perked up immediately.

    Following that and my own suspicions, I researched and there is quite a bit of stuff on the 'net about unvented heaters and their bad effects on us...and on plants. So...take that for what it's worth, but I'm offering my own experience of 2 full winters and a couple months extra....it seems likely to me.

  • martini100_gw
    9 years ago

    I have heard that too but also heard that the extra CO2 is very beneficial to plants. My basil did very well at first (big huge plants) but is struggling now. I believe it is an insect problem though. And the plants are old.

    I think you'll be fine with unvented propane for a month or so. Keep a window slightly opened if you are that concerned about carbon monoxide.

    Just my two cents!

  • sand_mueller
    9 years ago

    I also use unvented Mr. Heather propane heaters. My greenhouse is leaky and have had no problems. My plants look great. In Houston used a huge alligator heater, burning kerosene during rare freezing night...no problem with that either.

  • benfisher
    9 years ago

    i have used an unvented type LP unit. if it burns correctly the only by-product of combustion is carbon dioxide and water. our little unit has a Carbon monoxide detector built in that will shut off the gas supply if an unacceptable amount of CO is detected. I think the plants love the CO2! I also run a twelve volt mini fan to move a little air. It will run for a week on a charge with a low speed fan on a decent car battery. I converted a little ice fishing shack last year when our spring would not commence!


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