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Thread: Condensation buildup in Water heater exhaust

  1. #1
    DIY Member Squints2See's Avatar
    Join Date
    Jan 2005
    West by God Virginia

    Default Condensation buildup in Water heater exhaust


    Im trying to figure out the best way to solve a problem I am having with moisture buildup in the exhaust of my high efficiency gas water heater. I am using 3" PVC and it is ducting horizontally about 70-80 feet before exiting the house. Every few weeks the water heater stops working because of the water buildup in the exhaust line and I have to take apart a joint in the line and drain the water. It is probably 2-3 gallons. I am well within the length limitations stated in my owners manual for the length of exhaust line specified at the 3" size i am using. (It says i can go up to around 160') Am I going to have to put drains in the line to stop this, or can I just put a slight angle on it so it slopes towards the outside? I could do that for part of ithe run but not all of the run. It is possible that I could exit the house another way and shorten the run about 25', it would just be a pain to do. Would shortening the run help?

    Any help would be greatly appreciated.

    Todd in WV.

  2. #2
    Plumber jimbo's Avatar
    Join Date
    Aug 2004
    San Diego


    I would check the install manual for that heater. It probably does not allow horiontal pipe.....i.e. the exhaust probably has to slope to the outside, or back to the inside, but probably should not be dead flat to allow moisture to accumulate. Check the book.

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    The alternative is to do what they do with condensing boilers and things like that...add in a drain fitting to the exhaust line and then run it to a condensate pump. It gets a little messy since you also need a trap to block the exhaust gasses. My guess is that they either didn't install one of these as required, or they didn't follow the instructions and pitch the line outside. That is a very long exhaust path and it is normal that they're be a good quantity of condensation...it needs to run somewhere. If you can't let it run out, then you need to drain it out.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014


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