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  1. #1

    Whole House Dehumidifer won't work - So Hybrid?

    After living in our new Philadelphia suburb home for a two months, I see that I'm going to need a dehumidification in the basement, downstairs bedroom, and the upstairs laundry area for the spring and fall. These areas have the most mildew / mold spots on the paint. My first thought was to get a whole house dehumidifier and connect it to the downstairs HVAC system. I cannot do this because the main supply in not accessible because it is in the slab and the AC coils are right on top of the slab. I've also read that the dehumidifier hookup needs to be about a foot or more from the AC coils. The home is 2900 sq ft, has an furnace and AC unit for each floor place in the basement which is on the 1st floor. The 1st floor shares space with the basement.

    So my other thought was to have the dehumidifier such as the Santa Fe Classic placed in the basement with the return drawing air from the downstairs bedroom or from the upstairs hallway and have the supply send the air to the downstairs bedroom, the basement, and to the 2nd floor laundry room. The longest run would be about 25 feet. My think the return that far away we would have some negative pressure going on, but I don't think that would be an issue.

    The Santa Fe Classic has a 275 CFM blower, and does 3 L/kWh sized for 2500 sq ft at 110 pint / day and a MERV 11 filter. I might change it for a cheaper Aprilaire 1770, but it ins't as efficient.

    What are your thoughts? This unit would run primarily in the spring and fall with the AC units doing the work in the summer. I attached the drawing on the unit placement with the ducts and a picture of the home.

    Thank you - Jeff
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  2. #2
    Join Date
    Sep 2009
    Location
    Arnold mo
    Posts
    3,956
    My first question would be to determine the cause for the high humidity in the home. Is it moisture intrusion from the ground in the basement, or in the case of the upstairs laundry room, is it being created internally in the house? I don't think Philadelphia has high humidity problems, but I'm in Missouri, so I don't know without checking it out. I wouldn't start spending money on any solutions until the problem is properly identified.
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  3. #3
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,060
    Dryer vent /washing machine leaking infiltration in basement as stated by tipsrfine determine why it is localized.

  4. #4
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Do you have access to the returns at least? It's possible to draw air from the return and return it through the return. Or you can install the dehumidifier independently and duct it to a from those rooms with relatively small ductwork.

    I agree with the above. I'd locate the humidity soruces and consider just adding ventilation if needed. Unless you have serious basement leaks and drainage issues, just a simple portable dehumidifer in the spring and fall should be more than adequate. Not worht the cost and expense of anything more substantial.

    I'm also wondering if the dryer vent is leaking or there's an issue with the window flashing or even a roof soffit leak comming dow nthe walls or something.

    I have a 86 y/o home in SE Iowa (more humid that philly, less than central MO) with full basement with no vapor barrier and have no humidity or moisture issues year round. But my basement has no leaks, is well drained and dry. My laundry is in my kitchen and dryer vent is well sealed.

  5. #5
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,336
    Quote Originally Posted by jeff.c.brown View Post
    After living in our new Philadelphia suburb home for a two months, I see that I'm going to need a dehumidification in the basement, downstairs bedroom, and the upstairs laundry area for the spring and fall. These areas have the most mildew / mold spots on the paint. My first thought was to get a whole house dehumidifier and connect it to the downstairs HVAC system. I cannot do this because the main supply in not accessible because it is in the slab and the AC coils are right on top of the slab. I've also read that the dehumidifier hookup needs to be about a foot or more from the AC coils. The home is 2900 sq ft, has an furnace and AC unit for each floor place in the basement which is on the 1st floor. The 1st floor shares space with the basement.

    So my other thought was to have the dehumidifier such as the Santa Fe Classic placed in the basement with the return drawing air from the downstairs bedroom or from the upstairs hallway and have the supply send the air to the downstairs bedroom, the basement, and to the 2nd floor laundry room. The longest run would be about 25 feet. My think the return that far away we would have some negative pressure going on, but I don't think that would be an issue.

    The Santa Fe Classic has a 275 CFM blower, and does 3 L/kWh sized for 2500 sq ft at 110 pint / day and a MERV 11 filter. I might change it for a cheaper Aprilaire 1770, but it ins't as efficient.

    What are your thoughts? This unit would run primarily in the spring and fall with the AC units doing the work in the summer. I attached the drawing on the unit placement with the ducts and a picture of the home.

    Thank you - Jeff
    Set the dehumidistat at 50%RH and let is run when the space is +50%RH. Most do not realize that the outdoor dew points of +60^F plus the moisture generated by the occupants combines to raise the indoor dew point above the wall and slab temperatures.
    I like your concept. Another assist would be to operate the a/c fan on low for several hours everyday to dry out the ducts that are in the beneath the slab. Keeping you indoor lower level humidity <50%RH will fix this. Fresh air for the occupants is another issue. Fix the moisture level problem first.
    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"

  6. #6
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,837
    Unless the doors between rooms in your home are weather tight, the location of the WHD is not really critical. You can use any one you want and duct it or not, your choice. I've installed several with minimal ductwork in wet basement areas and they've done a fantastic job of drying the whole house. It is likely that moisture from the basement is making its way up to the laundry and then condensing on cooler walls in the bathroom or laundry room. It is virtually impossible to change the humidity level in one area of your home and not affect the entire home. So put the WHD in the most choice spot and plug it in! Don't forget a condensate pump to remove the gallons of water from the house. Take care the discharge from the condensate pump isn't going to freeze anywhere should the system need to operate in frigid weather.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  7. #7
    To Answer some questions from the earlier replies:

    The high humidity is being in Philadelphia where 90+ humidity is common.

    The laundry room side is in the shaded side of the home which is the bigger culprit than the dryer. The dryer is ducted 3 feet to the exterior which is sturdy and intact. The basement floor is dry.

    In regards to locations...I've thought about also just plugging it in the basement and let it work. I didn't know how much it will affect the rest of the house...I could allways duct it later.

    In regards to the small portable dehumidifers, I would need to buy a new one every year and it takes more $$ to run, so I want to stay away from that.

    Thank you for your inputs!


    Jeff

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