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  1. #1
    Join Date
    Jun 2007
    Location
    Bucks Co PA
    Posts
    367

    Conditioning an Unfinished Basement

    Just finished reading the University of Minnesota Extension about moisture in basements, but still have questions.

    Background; I'm the original owner of a house built in 1988 in PA. The builder hacks left numerous leaks in the supply and return ducts which I sealed. They used duct board which I now know is a poor choice.

    After sealing I noticed a stale musty air in the "unfinished" basement. I remedied this by opening a small 3"x6" opening in the supply duct in the basement. This seemed to work well except the humidity continues to be somewhat of a problem although not as great.

    I had Radon remediation done which included a 24x7 fan drawing from two vents placed into the slab.

    I just had an Infinity 16 heat pump and oil furnace installed which works exceptionally well. The installer insists I close the 3"x6" "vent" in the supply duct.

    I don't want to do this because of my previous problem (stale musty air). The metal duct work just installed going from the system to the duct board is sweating heavily. They will come back to wrap the metal.

    My question; what down side is there to leaving the 3"x6" opening in the supply duct? Will it be worse than having stale musty and more humid air?
    .

  2. #2
    Join Date
    Mar 2008
    Location
    Central Maryland
    Posts
    246
    Quote Originally Posted by Jack2007 View Post
    After sealing I noticed a stale musty air in the "unfinished" basement. I remedied this by opening a small 3"x6" opening in the supply duct in the basement. This seemed to work well except the humidity continues to be somewhat of a problem although not as great.
    Sealing leaky ducts into conditioned space means more air where it was supposed to go, and less where it was going. In this case, you may have created the musty problem by removing conditioned air flow from your basement.

    Quote Originally Posted by Jack2007 View Post
    I just had an Infinity 16 heat pump and oil furnace installed which works exceptionally well. The installer insists I close the 3"x6" "vent" in the supply duct.
    So close it, and then open it again when he's gone. If you're getting enough air to the rest of the house, who cares?

    Quote Originally Posted by Jack2007 View Post
    I don't want to do this because of my previous problem (stale musty air). The metal duct work just installed going from the system to the duct board is sweating heavily. They will come back to wrap the metal.

    My question; what down side is there to leaving the 3"x6" opening in the supply duct? Will it be worse than having stale musty and more humid air?
    .
    I have a basement (w/ RADON remediation) in MD with 2 duct vents. I leave them open. They pull air from the main floor supply ducts, which is OK because enough cold air comes down the stairs from the second floor to make up for the loss.

    Unfortunately for me, in the Summer they don't provide enough dry air to keep the basement from getting musty. I added a refurb 50 pint dehumidifier, and within a few days the musty smell was gone. I still leave the ducts open though, because all the parts of the house need fresh air.

    It sounds like you may have a more borderline situation, where just having a vent in the basement is enough to make the humidity difference to get rid of the mold/mildew musty smell.

    So, you can add a dehumidifier (with its attendant issues of adding heat to your basement and a few dollars to your monthly electric bill), you can add a vent without telling your A/C company, or you can negotiate with them to have them add an "official" vent.

    In my opinion, they work for you, and if a vent is needed in the basement, they should figure out a way to make that work. If it was not negotiated ahead of time, it may cost more $$, but adding a single vent to existing duct in an unfinished area shouldn't be prohibitively expensive.

    -HF

  3. #3
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,585
    If you qre serious about controlling humidity to the point where there is no musty odor get a decent dehumidifier. The a/c only control %RH when you have significant cooling load. A home with good IAQ has 50 cfm of fresh air when the home is occupied. Thats a 2-3 lbs. of moisture per hour when the outdoor dew point is +65^f to maintain <50%RH. Most people have no clue about the need for Fresh air and low humidity. Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  4. #4
    Join Date
    Jun 2007
    Location
    Bucks Co PA
    Posts
    367
    Quote Originally Posted by teddy bear View Post
    If you qre serious about controlling humidity to the point where there is no musty odor get a decent dehumidifier. The a/c only control %RH when you have significant cooling load. A home with good IAQ has 50 cfm of fresh air when the home is occupied. Thats a 2-3 lbs. of moisture per hour when the outdoor dew point is +65^f to maintain <50%RH. Most people have no clue about the need for Fresh air and low humidity. Regards TB
    I have been investigating ways to control "pollutants" in the HVAC system (mold), but guess I should instead be looking for ways to bring fresh air into the house via the HVAC somehow.
    .

  5. #5
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,585
    I suggest killing two birds with one stone. Use a dehumidifier with a powerful duct fan to introduce fresh air from outside, mix the fresh air with house air, filter both, and introduce the air to your basement and a/c ducts. When the %RH excedes 50%RH, the dehumidifier will operate. The dry air will keep the ducts and basement <50%RH. Check out the Santa Fe/Ultra Aire whole house ventilating dehus. Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

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