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Viessmann Coaxial Venting.

ViessViess Posts: 58Member
Howdy everybody! Hey I had a WB2B installed 2 winters ago and it's been running like a champ. The only thing I don't like is the frost it's leaving on my house. It direct vents straight out the back wall it's mounted on. The vapor rises up and runs under the eve and turns to frost. With some moisture getting into the attic and I don't want that. I would like to run the coaxial vent above the eve but it has to be run on the outside. Do they make an insulated coaxial vent pipe? I'm up north and it's dam cold at times, -20 is usually as cold as it get. Later on this summer I'll have the company that installed the unit come and do the work. Thanks Viess.


  • meplumbermeplumber Posts: 678Member

    The condensation that is coming from the vent is normal and it is actually a good thing.

    When your boiler is running at it's peak efficiency the flue gases are only around 100* F. That means that you aren't wasting heat out the chimney. It is all going into the house, where we want it.

    The drawback is that the flue gases contain a large amount of water vapor. The solution is with careful location of the vent termination. We try to be mindful of the proximity of things like side wall and roof overhangs. But sometimes, there is no other choice. Moisture in your attic is not a good thing.

    There is a Roof Kit that would allow the boiler to be vented through the roof. I have used it many times when there were other factors involved. However, if the distance from the boiler through the roof would cause the venting to exceed 26 feet of developed run, then this isn't an option.

    Express your concerns to the installing contractor and see what he can come up with.

    Good Luck.
  • icesailoricesailor Posts: 7,265Member

    Install a sheep (metal or plywood) that extends to either side and in front of the vent with some air space  between the sheet and the roof overhang so that the condensate collects on the sheet and not the roof overhang.

    The soffit vents should be blocked within the specified distance for the openings in the vent terminal instructions. I have always considered soffit vents in the same category as windows, doors and fresh air openings. The exhaust has no business in the attic. And yo have no business up there smelling it if you can.

    I personally would consider it a faulty venting. Even if an AHJ approves it.

    A sheet or plate will diffuse the exhaust out and away from the termination.  
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