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Thread: Greenhouse

  1. #1

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    hey everyone I am DYING to get my plants into my greenhouse but its way too cold, I need a way to insulate it, I want to try bubble wrap, but I dont know if I can use regular bubble wrap or not. If I cant use regular, can you point me to a place with the right stuff?
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    Tony Paroubek's Avatar
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    Regular bubble wrap will work. But even that will only add a small measure of insulation. What temperature are you trying to keep and how are you heating etc? and what plants are you wanting to put into it??

    Tony
    Is that a Nepenthes in your pocket or you just happy to see me?

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    well I guess I should get a space heater or something, no heating, trying to keep it at 40 lowest, Sarracenia, Dionaea, Some neps possibly, mmainly for sarras though, i just want to get some of them ready so i can take them to the flower shows in april, and some of my sarracenia are getting pitchers to tall for my indoor setups
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    In my two greenhouses all i have are space heaters, and they are doing very well. My advice, move tolerant plants go in first. I am glad the first plant i put in my first greenhouse was a ventricosa, since it failed a few times, and got to 35 degrees.

    My advice, get a really good space heater, and be prepared to blow fuses, it happened to me at least twice a week (getting to 35 degrees) until i finally figured how to get it right.
    Update: Parents convinced to allow me to keep greenhouse heated over winter. Most species will not be lost. Too lazy to update growlist.

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    well every night here it gets into the twenties and teens, would it be effecient enough?
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    Tony Paroubek's Avatar
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    You must plan your heating needs based on the coldest it might get. Even if it only goes to -20 every few years. That is the number you use in judging how much heating capacity you need.

    How many BTU's you need will depend on the Warmest Temperature you are trying to reach on the coldest night. It will depend on the surface area exposed to the cold and the material used on the walls of the greenhouse.

    So for example you want to achieve at least 45 at night. 45 - -20 = 65 temperature difference. Calculate the surface area of the greenhouse walls and roof. 6 x 8 with a 6' high sidewall and 8' tall ridge = 238 sqft

    Surface area x temperature difference x 1.1 = BTU
    Rough estimate 238 x 65 x 1.1 = 17,000 BTU if using single layer covering -30% for twinwall polycarbonate or other double layer covering. or 12,000 BTU of heat. This is a conservative estimate. The IGC calculator came up with 9,600 BTU.

    A 1500 watt heater puts about about 5,000 BTUs and draws about 12-13amps
    You will need 2 heaters to reach the 45 degree mark when the coldest temperature is -20. On warmer nights you can keep the greenhouse warmer or just set them for 50 and they won't run as frequently. Insulating with bubblewrap or something else at least on the walls would help alot also. I would still recommend 2 heaters in either case. Your safer with 2. Bubble wrap will just help hold the heat longer so the heaters run less.

    The real kicker is the energy cost.. A 1500watt heater uses 1.5kilowatts/hour. I don't know your energy cost out there but off the top of my head mine is about 13cents/kwatt SO.... to run ONE heater for ONE hour it would cost 1.5 x 13 = 19.5cents. (the hard part is calculating how long your heater will run each day. The best you can do is estimate. Without added insulation I would expect that the two heaters would run for about 8hours at night and only minimally during the day if it's sunny. If it's cloudy then they will be on a good portion of the day also. So figure roughly 10hrs a day the heaters are running. 19.5cents x 2heaters x 10hrs = 3.90cents per day. or.. $3.90 or... x30days = $117/month in electric heating cost)


    You can go through and use actual greenhouse calculations, temperature differences, electricity cost etc as I estimated a number of things based on your 6 x 8 greenhouse.

    Tony



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  7. #7

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    You might also consider passive heat storage.
    Some people line the north wall of their greenhouse with gallon jugs of water or sometimes even use 55 gallon metal drums filled with water(painted black). Water slowly releases heat all night so your heater would not have to run as much.
    The water will not keep temperatures very high but definitely help keep it above freezing.

    Kirk Martin
    Fitchburg Mass

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