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  1. #1
    Join Date
    Oct 2003
    Posts
    63
    I have a 4" PVC fresh air intake. I have run it up to 6' above grade and put a U at the end so that the intake is facing the ground. But the suction is enough that when we have heavy rain the intake sucks in a lot of water.

    Are there any tricks to preventing the intake from taking in water, short of building a roof over it?

  2. #2
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,981
    More then likely it is condensating inside of the pipe, not sucking water in. 4" pipe is a bit large and will condensate quite a bit of moisture from the air.

    In any case, you should have a trapped drain on the combustion air pipe close to the furnace.

    Concentric terminated vents have the issue much less due to the prewarming of the combustion air.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  3. #3
    Join Date
    Jul 2004
    Location
    midwest
    Posts
    2,868
    Are you talking about a fresh air for furnace combustion or a pipe that is tied into your cold air return? I have never had this problem on combustion intakes and if its fresh air for return you have a problem with your duct work if its pulling enough to get water to come in the pipe.

  4. #4
    Join Date
    Oct 2003
    Posts
    63
    This is a fresh air intake leading to the cold air return, not furnace/make-up air. It's definitely sucking rain in -- not condensation. I have a FilterVent pulling 75CFM through the pipe, so it's like 1" w.c. of suction. Definitely enough to get rain falling/dripping around the opening.

    Once it crosses to the inside of the house the intake connects to a 6" insulated flex duct. Maybe a trapped drain is the solution? Not sure how I would do that on 6" round duct though.

  5. #5
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,981
    Sorry, I misunderstood.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  6. #6
    Join Date
    Sep 2003
    Posts
    1,311
    Put a PVC plug on the intake; That will take care of it!

    If you can find it check out the Rheem condensing furnace direct vent alternative installation diagram. They address that type of problem by installing a T (in your case 4") in such a way that it will trap the water. The side of the T that traps the water has a reducer and then comes off with a hose (about 1/2"). The hose is looped to form a water trap in mid air.

  7. #7
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,429
    Originally posted by dbooksta
    This is a fresh air intake leading to the cold air return, not furnace/make-up air.

    It's definitely sucking rain in -- not condensation.

    I have a FilterVent pulling 75CFM through the pipe, so it's like 1" w.c. of suction.

    Definitely enough to get rain falling/dripping around the opening.

    Once it crosses to the inside of the house the intake connects to a 6" insulated flex duct. Maybe a trapped drain is the solution? Not sure how I would do that on 6" round duct though.

    Keep It Simple __ Expand That Sucker

    SLOW the air down DIRECTLY AT the Inlet ...
    IN Other words,
    ______________ expand 4" PVC to a ~ 6" inlet

    Material
    1. 4" by 6" Expander (reducer, if you will),
    2. 6" diameter PVC x 12"

    4" dia., 75 CFM = 860 FPM ... Entrains Water Droplets ! !!
    6" dia., 75 CFM = 380 FPM ... Resolved ?

    Velocity pressure is reduced by > 4 X

    ( or as the more dramatic persons wish to
    state ' by more than 400% ').

    Note: 4" diameter = 12.5 sq. inch,__ .087 sq feet
    ....__6" __________ 28.3 .........__ .196
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  8. #8
    Join Date
    Oct 2003
    Posts
    63
    Excellent solutions -- I'l try enlarging the intake and if that doesn't work I'll put a T-trap on it.

    Thanks!

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