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ModCon Termination velocity

Xc8p2dC_2 Member Posts: 150
My thought was more for external noise, being located near bedroom windows, it was suggested to run 2" for fitment issues, but I could see [or potentially hear] issues as you all suggested


  • Xc8p2dC_2
    Xc8p2dC_2 Member Posts: 150
    Exhaust sizie

    Looking at many pics of the ModCons, most seem to have 3" or 4" PVC Exh/Intk piping. If a smaller dia pipe is used for the Exh, will it create a higher velocity output and therefore the potential a noisey'r termination?
  • Brad White_9
    Brad White_9 Member Posts: 2,440
    If you stick your ear

    next to the nozzle you will have other problems too. :)

    They to make a gentle roar in my experience but overall as a system they are quieter than conventional boilers both inside and outside.

    The velocity is essential for dispersion and to avoid re-entrainment I am sure you know, especially with concentric venting systems.
  • hr
    hr Member Posts: 6,106
    Not only the discharge

    but the velocity increase is seen on the intake side pipe. They become a mini vacumn cleaner. Beware any slow flying insects that get too close :)

    Interestingly enough Polaris still uses a 2" vent with their 100K unit. And they include an intake air filter assembly. Most have gone away from the vacumn cleaner style fan and the new Polaris, for one, is much quiter with a newer technology fan assembly.

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  • Guy_6
    Guy_6 Member Posts: 450

    The downside to downsizing the termination is that these units typically operate on a CFM:BTU ratio. If you choke down the exhaust, you are in effect, reducing the output ability of the boiler. Fortunately, you are NOT taxing the HX by trapping excess heat within, simply reducing the boiler's ability to MAKE the full BTU rating. I have had great success by simply extending the full sized exhaust termination by as little as 3 inches to project the flue gasses out further.
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