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How hot do exhaust temps get on a Navien combi boiler, and is it safe to glue the joints?

JohnJr Member Posts: 14
edited September 2021 in THE MAIN WALL
How hot do exhaust temps normally get on a Navien combi boiler? I won't be adjusting the water temps already set by default on the boiler (140F). Will schedule 40 or 80 PVC work, and is it okay to glue the joints of the intake and exhaust pipes (excluding the section going into the boiler that joins up with the gasket)? How how do these exhaust pipes get also? I've also noticed that supplyhouse.com has a Polypropylene venting pipe, but the joint lock together with a metal bracket or hose clamp. Which type would be more effective and/or safer in terms of preventing leaks and withstanding exhaust temps? Thank you in advance!


  • Jamie Hall
    Jamie Hall Member Posts: 22,928
    Um... what does the manual say? I doubt very much that it allows PVC -- either schedule -- as the maximum temperature for PVC is 140 F. And the exhaust will be over that -- sometimes well over that.

    I certainly wouldn't want the stuff serving as an exhaust pipe...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • JohnJr
    JohnJr Member Posts: 14
    @Jamie Hall Believe it or not Navien's manual states that Schedule 40 or 80 PVC Solid Core is recommended as the default venting pipe for its boilers. However, if you require to adjust the water temperature on the boiler above 140F, it is recommended to use an approved CPVC, Polypropylene, or Stainless Steel venting. I've made up my mind and am going with 2" UV resistant polypropylene for the exhaust and intake.
    EBEBRATT-Ed Member Posts: 15,329

    Good choice. Everyone use PVC in the past but some locations and some boiler MFGs have outlawed it as it is really plumbing pipe and most (but not all) pvc pipe mfgs never tested it for flue gas.

    Polypropylene is the way to go

    BUT you can use PVC for the air intake with no issues and save a few $$$$$