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popping noise from vent

doctim Member Posts: 1
New home in the mountains of Colorado. We have radiant floor heating run off a natural gas boiler.  Vent for boiler makes popping noise randomly. Noise seems to be coming from near the top of vent. Noise is loud and irritating inferring with sleep. Plumber has checked boiler and says it is operating normally and correctly.  Calls problem "steam bang" and only solution is to run vent a different way but won't guarantee running the vent in a new direction will eliminate the popping noise.  HELP! I'm frustrated after spending money on a brand new house that I'm having this bad noise. None of my neighbors have such a problem!! 


  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    edited January 2011
    Steam bang???

    Personally, sounds like square btu's being stuffed into a round pipe... The corners catch quite often and cause a bang when they release... (If you buy THAT theory, I've got a LOT of other unused ones I'd like to sell ;-))

    The ONLY case of alleged "steam bang" I have ever heard of, and haven't actually witnessed it, is when a mod con boiler is installed with a trapped horizontal vent. I've been told that as the hotter flue gasses travel past the pooling condensate that it can flash to steam, causing a BANG. Having never improperly installed one, can't say I've ever heard it.

    What I have heard however, is the constant expansion/contraction of the PVC venting system when they are completely bound up on both ends due to the use of conventional mechanical clamping technology. Plastic has a coefficient of expansion of 1.1" per hundred feet length per 10 degree F change in temperature. So, a vent 40 ' long, when going from 70 to 170 degrees F will grow 4.4"'s If it is allowed to jerkily slip through the mechanical connectors, then it can click, tick and bang when it is expanding, and will do the exact same thing, but slower, when it is contracting.

    If it were tightly secured near the bottom, and allowed to slip through all the connectors between there and the roof, it would do so without noise. The trick is placing slip collars over the pipe to allow it to slip, but keep it in check as it pertains to vertical alignment.

    The other trick is providing a seal at the top where it is going to be doing all its travel, and still maintain a weather tight connection. Even with the best of neoprene collar seals, this continuous sawing back and forth will eventually cause seal failure and leakage at the base of the stack. Time for someone to invent a new, better means of penetration that will accommodate this back and forthing...

    Where in the beautiful hills of Colorado are you located? Blackhawk per chance?

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
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