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Max exposed vent lengths

Gordan Member Posts: 891
The TT Prestige venting manual supplement has the max exposed (e.g. outside the building envelope) vent lengths of 24" away from the wall, and 24" up (12" for the air intake) from the wall penetration. The language explaining this restriction states that exceeding these lengths would create a risk of condensate freezing in the vent and creating a blockage and a hazardous situation. If one needs to go longer than this in order to properly clear the max anticipated snow fall, what would be some options to do that? Going inside the sidewall is not an option - no room for that. Would insulating the vent pipe be acceptable, and if so, by what means?

The manual also states that the vent and air penetrations shall be a minimum of 12" apart. I know that the horizontal distance between the terminations is critical, but why would the distance between the pipes at the penetration matter?


  • icesailor
    icesailor Member Posts: 7,265
    Vent length separation:

    It is to keep the exhaust fom possibly being sucked back into the intake.

    Fondly known as "regurgitation". And it happens.
  • adambuild
    adambuild Member Posts: 406

    Hi Gordan,

    I just went through this same situation call me on my cell and I'll give you the options and explanations.

    Adam @ 973 area code, 670-2095
  • Gordan
    Gordan Member Posts: 891
    Yes, I'm aware of that with regard to the terminations.

    That doesn't have anything to do with how the pipes are routed before the termination, notably, at the wall penetration - right?

    After all, at the boiler the intake and vent ports are only a couple of inches apart.

    It's not recirculation, that much I can figure out on my own. What I'm hoping is that there's not something else that I'm missing.
  • Henry
    Henry Member Posts: 995

    No matter if in the US or Canada, yo must follow the manufacturer's certified instructions for vents and combustion air. If certain situations are not covered by the manual, a derogation can be had usualy with a letter from the manufacturer. From personal experience, insulating the vent will help to overcome 24 inch as some manufacturer's manuals state. But I have tested properly sloped vents that return the condensate to the boiler or furnace that can have longer lenghts. But this only applies if the manufacturer of the appliance will give you a letter stating so.

    My own hot air furnace has 5 feet exposed with no side effects. It is acceptable by the manufacturer. One year due to atmoshperic conditions, I had a 4 foot stalagnite formed. It did not block the vent but would if it was 24 inches off the ground. I will try to locate the pic. Regional situations are not covered when a manufacturer certifies his venting condition for his product. Some more proactive manufacturers will ad to their venting instructions words such as: local conditions may necessitate alternative venting, contact the factory for instruction, etc...

  • icesailor
    icesailor Member Posts: 7,265
    exposed lengths:

    Sorry, I misunderstood the question.

    What you are asking, I've wondered myself when you try to get above projected show levels. And what to do when the vent termination is on a lee side and you know that you could easily get a 6' drift over the intake/exhaust. In Massachusetts, we are required to post a plastic sign 6' up above the vent termination so anyone can locate the termination.
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