High Wind causing Limit Switch to Trip now glacier after installing elbow pvc help! - Page 2
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  1. #14
    Join Date
    May 2006
    Location
    Philadelphia, PA
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    1,374
    What is the brand and model number of the furnace, and what is the total length of vent pipe?
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  2. #15
    Join Date
    Feb 2013
    Posts
    6
    Quote Originally Posted by comfortdoc View Post
    What is the brand and model number of the furnace, and what is the total length of vent pipe?
    The brand is: Intertherm/Nordyne
    Model is: M3RL-080-A-BW +90

    I can't tell you the exact total length of the vent pipe but it's gotta be 10 foot or more..I've enclosed a picture showing the pipes from a distance. Again, the intake pipe had a (what I'm calling a 90 degree) pvc elbow on it when I moved in...BUT the exhaust had nothing..it was just straight up in the air (no slope that I could tell) and when the vent switch tripped, everything, including compression tests etc were performed and the conclusion from the two techs was that it was either a faulty switch or off the top of his head it was a high wind (which there was gusts to 80 mph prior to tripping.)

    I'm the one who put a 45 degree elbow but just before snowfall I thought I should make it a 90 degree (just like the intake and point it easterly)...didn't think about the fact that the water would drip down at the time but in my defense I don't work with this stuff nor was I familiar with the winds up here.

    There is a couple areas where icing is occurring where it can seep out but that really doesn't seem to be problematic..I could seal that better but still the whole design is not right. I could put it back to just a 45 degree config BUT I think that will still allow for dripping and growing ice? I could put a high wind vent on but I think I would need to block off one side of it due to N & NW winds and I know that metal will rust and stain the roof..that's all I know at this point. I wish I could describe the config I think would work which would just be extending the straight pipe up say 10 inches but doing it with only pvc that's cut in half and attached to it...would block the wind but allow condensation to fall back down pipe. Hope this helps and really appreciate all the advise I'm getting on this forum, you guys are great.
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  3. #16
    Join Date
    Feb 2013
    Posts
    6
    Quote Originally Posted by tiger man View Post
    I would cut that elbow off asap on the exhaust, and get a bushing that is 2 inch, to 1 1/2 inch then a foot long piece of 1 1/2 pvc. The tech who was there should have done something like this, or find the reason the vent limit is tripping. Have him perform a combustion test as well
    I agree that the elbow will have to go but I'm left wondering if I do what you suggest above how this will help keep the wind from cutting off the exhaust from the 1 1/2 inch pipe, I realize going to smaller diameter would help if it was freezing inside the pipe but that is not an issue it's the negative pressure (if I'm saying that right) overtaking the positive outgoing exhaust. The height of the existing pipes is ok and with the way the wind blows at times the snow doesn't build up or stay on the roof it blows off and if it didn't I would have to get out the roof rake, but so far no issue with any blockage from snowfall, just wind. Thanks.

  4. #17
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,694
    Have you had 80 MPH gust since you put those ells on? If not, the you don't know if its helping.

    Wind gust should open the pressure switch. So I doubt you had a tripped vent limit switch from wind gust.

    Did you power go out anytime close to when you were having those wind gust.
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  5. #18
    Join Date
    Feb 2013
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    6
    Quote Originally Posted by beenthere View Post
    Have you had 80 MPH gust since you put those ells on? If not, the you don't know if its helping.

    Wind gust should open the pressure switch. So I doubt you had a tripped vent limit switch from wind gust.

    Did you power go out anytime close to when you were having those wind gust.
    Yes we have had several strong winds and the vent limit switch did not trip, so I believe the elbow fixed the problem...I may have made the elbow curve too much thinking a little more would be better and hence creating the glacier growing on the shingles but need an idea for a better design for next winter (and hope it doesn't create another problem like this idea.)

    As for any power outage, I do understand that it could cause the vent limit switch to trip (I was asked that by the tech at the time) but none had occurred around that time.

    I missed answering this on a previous response, but there is no screening material in either the intake or exhaust, just fyi.

    Appreciate your response and working with me on this.

  6. #19
    Join Date
    May 2006
    Location
    Philadelphia, PA
    Posts
    1,374
    Find an installer that is very familiar with that furnace. Be certain the vent size is correct for the length, and the position of the pipes is correct. Then have them look for the manufacturers recommendation on insulating exposed pipe for your outdoor conditions. If the manufacturer does not have guidance, check with your local building inspectors.
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  7. #20
    Join Date
    Feb 2010
    Location
    In a boiler room
    Posts
    7,043
    The vent limit trip is a very common problem on that model and has nothing to do with the termination or the wind.

    Your technician is fixated on the venting and overlooking the real problem.

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