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  1. #1
    Join Date
    Jun 2004
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    Thanks to all who responded to previous post on window condensation in my house. Per the advice, I was planning to call an HVAC guy today, but while poking around yesterday, I found something that seemed worth questioning

    I don't know anything about HVAC, but from what I can tell, there is no air inlet to my furnace - save the one that is on the outside of the house. This consists of a 6 (or 8?)" round duct pipe with an angled inlet cover. Presumably the air enters here, goes about 15' straight into my basement, enters a large chamber made of thin sheet steel and the I beams in my basment ceiling, turns 90 degrees and goes about 30' to the furnace.

    But here's the thing, If I'm outside my house and I look into the air inlet, it's blocked. There's some sort of butterfly looking valve blocking all incomming air.

    So I removed a section of the basement duct near the butterfly valve and looked at it. It's a purely mechanical valve made up of 2 flaps which pivot along the center of the round duct and seem to fold inwards (so incomming air (or a vacuum from the furnace?)) would cause them to open, allowing air in. Only, mine is stuck. It actually looked like it was painted there was a lot of 'overspray' on the foam gasket that helps make the butterfly valve seal. So, some questions:

    I assume this isn't supposed to be stuck?

    After I 'unstuck' it, I've run my air conditioner, heat, and just fan and looked at the valve under all 3 doesn't move/change...and remains just slightly open (which is how it looked after I 'unstuck' it. So it doesn't seem to pivot very well. Assuming this has been stuck for the 2.5 years since the house was built, could it be broken?

    It is feasible that my furnace has been pulling air from the basement(through duct joints, etc) for the past 2.5 years - so it didn't matter that I had a stuck inlet valve (although it might explain some of the moisture)?

    I assume this is a fairly commong thing that any HVAC guy could easily replace?

    Thanks for all of the replies! Jeff

  2. #2
    Join Date
    Jun 2003
    Madison, WI/Cape Coral, FL
    Post Likes
    WI requires make-up air without much detail. Suggest removing the damper and operating your fan furnace continuously until your windows clear. Check for suction at the outside of the vent to verify fresh air intering your home. Include a operting a couple of bath fans for a couple weeks or until the windows clear. The cost heating enough make-up air to clear the windows is less than $100 for the year. After you identify the amount of fresh air necessary to keep the windows clear, maintain the ventilation rate to purge pollutants and replace oxygen. Get enough dehumidification to maintain <50% in your basement through the summer. Next summer, if your current dehu fails to keep up , try a Santa-Fa on me. Keep us posted. A WI TB!

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