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Thread: fan in attic

  1. #1
    Join Date
    Apr 2008

    Default fan in attic


    I may have asked this before, but since searching on these boards is so onerous, I will ask it now.

    I have an old metal box fan that I put up in the crawl space/attic of a garage apartment. I leave it up there all year 'round. When it comes to be summer, I plug it in and it seems to help draw hot air out of the attic through the vent window it is next to. In the winter I lie it down. In the summer I prop it up and it stays put.

    My question is, is there any fire danger? I am home most of the time but can't monitor it all the time. I unplug it when I leave home or go to sleep.

    Could the extremes of temperature affect something in the motor, lubricants?, that might make it more likely to freeze up/seize when it is being used in the summer, causing a fire.

    Is it likely that whatever air it draws out could bring enough dust into the motor that that might cause a fire hazard? The attic is unfinished. I know there are the occasional bug up there, maybe a wasp's nest, but otherwise it is just fiberglass batting as far as I can tell.

    I have the accessway to the fan closed off with a screen now but I will inspect it if anyone thinks it is worth it.

    The fan is at least 20 years old and may be more than that. It's big and heavy. It would be protected from rain since it is far enough away from the vent.

    Please let me know if there is anything else I need to consider.


    John L

  2. #2
    Join Date
    Aug 2007

    Default Re: fan in attic

    You will have to check to see if the fan motor has a THERMAL CUTOFF SWITCH attached to its motor---there should be a label on the motor housing that indicates this---many box fans designed for a window do not have a thermal cutoff.

    A TC is designed to melt the contacts that make the motor connection at a temp of ~160-200 degrees if the motor overheats, thus preventing a fire.

    Google "motor thermal cutoff" for on-line sources---locally, Grainger would have these switches for a few dollars.

    You're taking a real risk of fire if you don't install a thermal cutoff on that motor.

    Another problem with the setup you describe is it sounds like you're not "boxing in" the fan to the gable vent---dedicated attic gable vent fans have a thermal cutoff & also a circular metal shell surrounding the fan that is bolted to the gable frame & the rest of the gable vent is blocked off so all attic air is exhausted thru the fan's metal shell cowling---this is the only way to get an effective exhaust of attic air.

    See the diagram at the Saven site below---in other words, just propping a box fan against the gable vent is ineffective & is going to waste electricity because the external air coming in the sides of the gable vent will short circuit thru the fan blades & very little air will be exhausted from the attic.

    Also make sure you have adequate open venting on the opposite gable wall or opposite side of the attic (the higher up on the gable the better) so that a good cross-flow of air can exhaust thru the fan.

    Last edited by JacktheShack; 06-11-2008 at 12:14 AM.

  3. #3
    Join Date
    Aug 2007

    Default Re: fan in attic

    The only other thing I would add to Jack comprehensive post is does the motor have oil holes that should be lubricated with a few drops of motor oil a few times a year or sealed bearings that prevent any maintenance. If the bearings fail the motor is likely to overheat.

  4. #4
    Join Date
    Apr 2008

    Default Re: fan in attic

    Thank you both very much. I will take to heart your advice. I don't want a fire so I have to think how I can use that fan to help cool things off in a safe way. I am not sure what I will do but I certainly won't be using it in the way I have been.

    It doesn't have a thermal cutoff switch and I don't think it has lube holes... I think it was reasonably effective at drawing air up and out but I will have to think of another way to do that that doesn't involve the fan being in a dangerous position.

    Thanks again.



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