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  1. #1
    Join Date
    Nov 2004
    Location
    Atlanta, Ga. burbs
    Posts
    281
    I am in the process of selling my current house (which has a basement) and buying a house with a crawl space.

    I know very little about houses with crawl spaces. Hence the problem I am reporting is foreign to me since my basement is conditioned.

    ======================================
    Today a certified house inspector came to the new property and here is what he wrote up on the HVAC:
    ======================================
    1- Have a licensed HVAC tech. come out and inspect/service the unit before I buy the house. (I agree and it will be done. I was going to do this anyway after the initial inspection.)
    2- He said the HVAC pipes, under the house are sweating, and there is some water dripping/puddling on the vapor barrier. (I assume supply pipes)
    3- He said there is a bit of mildew on the floor joists due to the sweating of the HVAC pipes (I assume supply)
    4- His suggestion is for homeowner to spray with bleach for the small amount of mildew. But he said the problem needs to be corrected which is water dripping from the flexi duct.
    5- His suggestion was a dehumidifier and to be sure a licensed HVAC tech. serviced the unit/make recommendations on how to solve the sweating.

    =====
    This house is in the Atlanta area.
    The outside temp. today was 100 (wet heat!!)
    Piping that is in question is flexi duct
    Air handler is in crawl space and unit is a goodman 6YO
    =====
    There will be an HVAC Tech. onsite in a few days and the credentials of this gentlemen appears to be great via referrals.

    I just want to be informed enough to be sure the right things are done before we sink our money into this house. The current homeowner has agreed to pay for the HVAC visit. But the current owner is also in commercial construction and I do not want him to attempt a bandaid since he is not HVAC trained.

    Any advice would be greatly appreciated. And I am not going to attempt any DYI stuff nor do I want the current owner to do anything. (However, even their realtor admits he is very difficult to deal with and he "knows" alot since he is in the construction business. Which makes me nervous.)

    I guess what I am asking is what would you Pro.'s do if this were your house?

    As always thanks for your advice.

  2. #2
    Join Date
    Dec 2002
    Location
    in a house, Appomattox, Va.
    Posts
    3,199
    Humidity from outside is condensing on the cooler inside surfaces. Need to seal crawlspace walls and good vaporbarrier on ground, then the dehumidifier will dry things out.

    My ducts aren't even insulated and they're not sweating with this setup.
    Col 3:23


    questions asked, answers received, ignorance abated

  3. #3
    Join Date
    Nov 2004
    Location
    Atlanta, Ga. burbs
    Posts
    281

    Should I keep the foundation vents closed?

    Q. Should the foundation vents be closed?

    Q. or should I add an exhaust fan to have air movement?



  4. #4
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,078

    Re: Should I keep the foundation vents closed?

    Originally posted by west_seth
    Q. Should the foundation vents be closed?

    Q. or should I add an exhaust fan to have air movement?


    Is the outside air humid in Atlanta? How will moving more outside humid air into a crawlspace stop the sweating? Cover the earth with plastic, close the vents, and get a adequate sized dehumidifier, need 100 pints per 2,500 sq.ft. Suggest a high eff. low temp unit like Santa Fe HC or S F Advance, 5 pints Kw eff. Keeping the crawlspace <50%RH stops condensation, mold growth, and helps keep the home dry. Check with thermastor.com Comments by a dehu salesman. TB

  5. #5
    Join Date
    Jun 2004
    Location
    Florida
    Posts
    556
    Aren't the vents required by code, or does that requirement go away if you install a dehumidifier?

  6. #6

    Re: Re: Should I keep the foundation vents closed?

    Originally posted by teddy bear
    Originally posted by west_seth
    Q. Should the foundation vents be closed?

    Q. or should I add an exhaust fan to have air movement?


    Is the outside air humid in Atlanta? How will moving more outside humid air into a crawlspace stop the sweating? Cover the earth with plastic, close the vents, and get a adequate sized dehumidifier, need 100 pints per 2,500 sq.ft. Suggest a high eff. low temp unit like Santa Fe HC or S F Advance, 5 pints Kw eff. Keeping the crawlspace <50%RH stops condensation, mold growth, and helps keep the home dry. Check with thermastor.com Comments by a dehu salesman. TB
    100 pints per 2500 sq. ft.? Does this requirement apply both to an 8 ft. high basement or a 4 ft. high crawl space?
    I'm asking because I'm working on improving my 4 ft. high crawl space in the SW corner of B.C. (your NW corner of Washington state).

  7. #7
    Join Date
    Nov 2004
    Location
    Atlanta, Ga. burbs
    Posts
    281

    I really dont' know

    I don't know that is why I am asking. The question about pulling the air out / not into the crawl space.

    10 years ago no one would have cared. But everyone who had allergies would wonder why me.

  8. #8
    Join Date
    Dec 2002
    Location
    in a house, Appomattox, Va.
    Posts
    3,199
    Vents are required by boca code if I recall correctly, BUT, that don't make them right, especially when you consider some codes are generic and are used across the country without consideration to local environment.

    In the North, vents will work well and you NEED them for attics in some types construction. In that part of country with cold climate, the vapor barrier is on the inside of house, but in hot humid climate like Georga, the vapor barrier should be on outside of wall.
    Col 3:23


    questions asked, answers received, ignorance abated

  9. #9
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,078

    Re: Re: Re: Should I keep the foundation vents closed?

    Originally posted by deme
    Originally posted by teddy bear
    Originally posted by west_seth
    Q. Should the foundation vents be closed?

    Q. or should I add an exhaust fan to have air movement?


    Is the outside air humid in Atlanta? How will moving more outside humid air into a crawlspace stop the sweating? Cover the earth with plastic, close the vents, and get a adequate sized dehumidifier, need 100 pints per 2,500 sq.ft. Suggest a high eff. low temp unit like Santa Fe HC or S F Advance, 5 pints Kw eff. Keeping the crawlspace <50%RH stops condensation, mold growth, and helps keep the home dry. Check with thermastor.com Comments by a dehu salesman. TB
    100 pints per 2500 sq. ft.? Does this requirement apply both to an 8 ft. high basement or a 4 ft. high crawl space?
    I'm asking because I'm working on improving my 4 ft. high crawl space in the SW corner of B.C. (your NW corner of Washington state).
    The recommedation has to do with the rim joist leakage and moisture movement from the main floor, plastic covered earth the crawlspace concrete basement floor to the space. Height make little difference.

  10. #10
    Join Date
    Jun 2002
    Posts
    460
    If you have water dripping from your flexduct, then the humidity level is probably approaching 90%. Get a hygrometer and measure the humidity level in the crawlspace. Mold and other issues aside, at 90% the wood moisture content can approach 20% over time. Floors will cup, joists lose some of their strength, etc.

    The crawlspace floor needs a 6 mil or better liner with edges lapped up on the wall the seams overlapped. You can completely seal the vents as long as there isn't a gas furnace (except for a condensing furnace vented with outside air) or water heater there. A 65-70 pint dehumidifer is much cheaper ($200-$250) than the Sante Fe ($1200 or more) and can get the humidity level down into the 50's for 2000 square feet, but these aren't quite as efficient as the Santa Fe (Say $1.70-$2.00/day to run versus $1.40/day for the Santa Fe 100 pint model), and the Santa Fe will definitely remove more water.

    DO NOT USE A FAN to vent the crawlspace -- it can make it worse. Venting the crawlspace in the south to "dry it out" in the summer is a joke. The dew point (e.g. absolute moisture content) of the outside air will almost always be higher than the crawlspace air, so when it cools down to the crawlspace temperature, the net effect is to increase the overall relative humidity in the crawlspace, not decrease it. 90 degree outside air at 45% humidity has more moisture in it than 73 degree air (typical crawlspace temperature) at 80% humidity or less.




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