Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit

Direct Combustion Air / Vent

Economizer Member Posts: 14
I would like to know if anyone has experienced problems with running unequal lengths of combustion air vs. vent pipes, and if you figured out why?

I have heard of problems with Weil McLain on that issue, and would like to get others experiences.  I'm looking to do that for a job with four Buderus GB142-60's.



  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Not me, but too soon to tell.

    I have a WM Ultra-3 80K boiler. The combustion air and. vent pipes are not exactly equal in length, but are pretty close. Right now I have only used it to heat my domestic hot water, though winter is coming up sometime. Probably going into the mid 50s tonight, but that will probably not get the heat to come on.

    I have studied this system, and the WM installation manual quite carefully. I get the impression that it would make very little difference if the lengths are the same or not. What can make the difference is if they are too long, and including the effective lengths of elbows, etc. Another problem is that the two pipes outside the house should be very close together (but no closer than a foot apart) so wind blowing across them would not cause pressure differences. Sort of like closely spaced Ts in hydronic heating systems.
This discussion has been closed.