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Soffit-Venting Evaporative Cooler Exhaust

wwarneke | Posted in General Questions on

I have a 1300 square foot ranch home in Metro Denver, which puts me in climate zone 5B.  A few years ago I installed an Energy Efficient Ducted Evaporative Cooler.  It works perfectly, and keeps the house very cool in the summer, even on the hottest of days.  My only concern is the need to have windows open to vent the stale “exhaust air.”  Keeping windows open is a security risk and poses a noise issue as well.

I have seen the Up-Dux barometric damper that allows EC exhaust air to be vented through the ceiling into the attic.  This seems to be just the thing I am looking for.  Theoretically, installing an Up-Dux in each of the bedrooms as well as a few in other parts of the house, should eliminate the need to keep windows open to vent the EC exhaust air.  But a couple concerns come to mind.  How wise is it to exhaust moist, relatively warm air into the attic?  Doesn’t that increase the risk of developing mold?  Of course, it would require that the attic be adequately ventilated so that any air added to the attic space could exit the attic unimpeded.

My problem is that my attic is NOT very well ventilated.  Just four basic “slant” vents, each of which has a 9″ diameter vent hole, which adds up to just under 200 square inches of total vent space, or less than 1.5 square feet.   Plus the soffit venting is basically non-existent.

In contrast, for a EC system like mine at 5000 CFM, Up-Dux recommends 4.5 – 8.5 square feet of vent space, so substantially more than currently exists.  I’m not really in a position at the moment to effectively revamp my attic venting system.  And even if I were, I’ve read that low slope hip roofs are quite difficult to vent adequately.

I actually had the roof replaced a few years ago following a bad hail storm, and soon after that the insulation was beefed up quite a bit thanks to a state sponsored “weatherization program.”  That would have been the best time to address the attic ventilation issue.

While I plan to eventually upgrade the attic ventilation, I’m wondering if it might be possible to vent the EC exhaust air directly outside through the soffit rather than dumping it into the attic.  I know the Up-Dux wasn’t designed to be used in conjunction with ductwork and would need to be reworked, somehow.  But what about using a few butterfly style barometric pressure relief dampers ducted up, over and down through the soffit?

What are your thoughts?  I’d really appreciate any advice or suggestions you’d be willing to give.  Thank you!

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  1. Expert Member
    BILL WICHERS | | #1

    My concern in the Denver area (I have family out there, so I'm familar with the climate) tends to get pretty cool at night. The risk I could see is if you pump humid exhaust air into the attic could risk condensation in the attic at night, and that condensation is a big problem.

    I think you'd be safer ducting the exhaust all the way out through the roof, using a suitably sized roof vent. You'd need more than a typical bathroom fan size vent, but you could potentially duct the exhaust up to something similar in concept to a gable vent. If you duct the air directly to a vent that goes to the outdoors, you eliminate the "moist attic air" problem. I would insulate the duct where it passes through the attic though.


  2. wwarneke | | #2

    Thanks for your reply, Bill. Your concern was exactly my concern. I'm not real keen on dumping humid air into a not so well vented attic. To be fair, the makers of Up-Dux are clear that any attic their product vents into needs to have adequate air circulation. That's where the 4.5-8.5 square feet of vent space recommendation came from. My attic has nowhere near that amount of vent space. I plan to add a ridge vent and soffit vents later this summer.

    Even so, I agree that ducting the exhaust directly to the outside is preferable. But my attic has no walls or gables to vent through. And given a choice, I'd rather not add any roof penetrations. That's why I asked if venting through the soffit were possible. Could I duct the exhaust air up through the ceiling, then over the exterior wall, and down through the soffit?

    If that's not possible, could I commandeer a couple of the slant vents that currently vent the attic, and duct the exhaust through them? Two of them happen to be almost directly above where I'm thinking about putting the Up-Dux vents.

    1. user-5946022 | | #3

      No, you cannot repurposes existing attic venting exhaust vents to vent this thing. They will then no longer be venting the attic and presumably your attic needs ventilation.
      HOWEVER, you can install a few new vents - what you term "slant vents" and use those for either exhausting venting of your attic while you use the existing for your Up-Dux, or leave the existing alone and install new ones for the Up-Dux.

  3. wwarneke | | #4

    Thank you for your reply, CL. Of course I know that the attic needs to be vented. I said I plan to install soffit and ridge vents. I have no desire to ADD penetrations to the roof to vent the EC if there are other options (like using existing vents that will be replaced by ridge and soffit vents, or ducting out through the soffit). I'm asking for advice on options that DO NOT include adding penetrations to the roof.

    1. user-5946022 | | #5

      Sorry. I did not, and still do not see where your original post stated that you plan to install soffit and ridge vents in the existing roof. I saw the statement of: "I’m not really in a position at the moment to effectively revamp my attic venting system. And even if I were, I’ve read that low slope hip roofs are quite difficult to vent adequately."
      Also you state you are asking for advice on options that do not including adding penetrations to the roof. A ridge vent is by definition a penetration to the roof. If there is no current ridge vent, you need to remove roofing, cut the decking back from ridge framing in order to create the penetration/continuous gap for the vent, then reroof with the ridge vent piece.

      1. wwarneke | | #6

        I made the statement about adding ridge and soffit vents in the message to which you originally replied. I did say in my original post that I am not in a position to revamp my attic venting, and I mentioned how difficult it is to vent a hip roof. But as someone who tries to learn as much as he can about how to complete a project correctly, I've spent much of the time between posts reading up and learning about venting a hip roof. From what I've read, a ridge vent along with continuous soffit vent appears to be the most effective way to vent a hip roof. And since it would be a huge improvement over four little holes covered by slant vents, I see that as a legitimate reason to penetrate the roof.

        In comparison, I am looking for advice on options for venting EC EXHAUST AIR without penetrating the roof. Penetrating the roof is necessary for venting the attic. It is not necessary for venting EC exhaust air. Maybe I should have been clearer and said I don't want to UNNECESSARILY add penetrations to the roof.

        Beyond all these discussions over semantics , I still have not had any responses that address the title question of my original post, "Venting Evaporative Cooler “exhaust air” though the soffit. Is it possible?"

        Now, I've just discovered that my post title got shortened to "Soffit-Venting Evaporative Cooler Exhaust," so that may factor into it. Either way, I still would like to know experts' thoughts on ducting EC exhaust directly outside through the soffit.

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