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  1. #1
    Join Date
    Sep 2004
    Posts
    6
    My question is in two parts:

    I think my house has a problem with negative air pressure. When the HVAC system is running (hot or cold), I get drafts from pretty much every single electrical outlet in the house (the windows are closed when this happens). The air is old, stale smelling and I have problems with allergies.

    Here's question 1: I know that I'm losing some air in the crawlspace where the ducts are. Should I assume that if I could seal all those leaks I would acheive equilibrium in the living area? Or can you alert me to other factors I should consider?

    Question 2 is related to loss of air in the crawlspace: I spent a half a day down there carefully taping every pinhole leak that could be found. The one I can't seal, however, is the biggest. It comes from the air conditioning coiling coil, which was poorly maintained by the previous owners and is rusted out at the bottom. I need to have that cooling unit replaced, but because of my allergies, I would like to have it relocated to the utility room where the furnace is located. My rationale is that it would then be far easier to clean/maintain the cooling unit while eliminating another opportunity for crawlspace air to enter the duct system. Is this the sort of thing a professional should be able to do for me? If so, what sort of precautions should I expect him to take? I don't want to introduce a critical error into the system.

    I intend to call a professional, but I'd like to get as educated as I can first. Thanks.

  2. #2
    Join Date
    Mar 2004
    Location
    SE Michigan
    Posts
    17,887
    1. make sure the duct is sealed and wrapped.
    2. Depending on how tight your home is, you may need a
    make up air kit.
    3. If there is room for it in the utility closet, have it installed in there. If you have a counter flow furnace, the furnace will need to sit on top of the coil.
    4. Have a hvac company come out for an estimate and request a manual j load calculation. This will tell you the proper size of furnace and a/c.
    5. Make sure that you have adequit return air for the system.
    6. Check into uv lights for your system. This will help your allergies.
    " Kill a Commie for Mommy! "

    - Colonel David Hackworth (1930-2005), Korean War Vet

  3. #3
    Join Date
    Sep 2004
    Posts
    6
    Thank you, coolwhip.

    I have one follow-up question:

    I've looked a bit on-line about make-up air kits. We could be talking about something as simple as a vent/duct that leads from the exterior of the house into the return, correct? I'm asking because I want to be aware of economical options in case the professional I contact tries to sell me an unnecessarily expensive one.

    Thanks

  4. #4
    Join Date
    Mar 2004
    Location
    SE Michigan
    Posts
    17,887
    Thats correct. Just a simple barometric damper.
    " Kill a Commie for Mommy! "

    - Colonel David Hackworth (1930-2005), Korean War Vet

  5. #5
    Join Date
    Aug 2003
    Posts
    626
    Leaky ducts will cause the home to go positive or negative. The best method is to have the ducts pressure tested with a machine called a duct blaster. This will show how much and where the leaks are.

  6. #6
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Best method is http://www.aeroseal.com seals and leak tests all in one operation.

  7. #7
    Join Date
    Aug 2003
    Location
    Central Kentucky
    Posts
    6,247
    Dash,

    I've heard that the aeroseal can only seal small holes in the duct system.

    Do you use an aeroseal machine? I would be interested to know it's limitations.

  8. #8
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Originally posted by davidr
    Dash,

    I've heard that the aeroseal can only seal small holes in the duct system.

    Do you use an aeroseal machine? I would be interested to know it's limitations.

    Yes, we have been doing it for several years.
    5/8ths of an inch wide by whatever size.


    It's real advantage is it will seal very small leaks,that would likely go unnoticed with hand sealing.


  9. #9
    Join Date
    Sep 2004
    Posts
    6
    gpl here (the original poster):

    Regarding the use of a barometric damper, I have three questions:

    1. Does a barometric damper just dump ice-cold winter air into the system? Or is there an economical way to warm the air a bit first?

    2. Will a barometric damper on the return air line neutralize only the negative pressure that is caused by the furnace blower? Or will it also help correct negative pressure that is caused by combustion appliances and exhaust fans?

    3. As I understand it, a barometric damper allows outside air to enter without dehumidifying it. In humid summer months does a barometric damper cause potential problems of excessive humidity in the system as a result?

    Thanks. This is one of the most helpful Web forums I've ever come across.

  10. #10
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    1. Yes

    2.Mainly the blower,but will help on the exhaust fans

    3. Humidity is the same ,whether thru the damper,or sucked in the the cracks in the building,with a damper you can at least filter the air


    Better to solve the main cause of negative pressure

  11. #11
    Join Date
    Sep 2004
    Posts
    6
    Dash,

    Thanks. By main cause, you're thinking it's probably the leaky ducts, right?

    If so, I'm beginning to think it might be smartest for me to . . .

    1. Remove my rusted out cooling coil, which is the biggest leak in the duct system. (There is an empty box under my furnace in the laundry room where a new one could go.)

    2. Seal all leaks in the crawl and see if the negative pressure persists before considering installing any sort of make-up.

    Does that make the best sense?

  12. #12
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Originally posted by gpl
    Dash,

    Thanks. By main cause, you're thinking it's probably the leaky ducts, right?

    If so, I'm beginning to think it might be smartest for me to . . .

    1. Remove my rusted out cooling coil, which is the biggest leak in the duct system. (There is an empty box under my furnace in the laundry room where a new one could go.)

    2. Seal all leaks in the crawl and see if the negative pressure persists before considering installing any sort of make-up.

    Does that make the best sense?
    Sounds like a good plan,adding a barometric may be good idea after the neg. pressure,is minimized.

  13. #13
    Join Date
    Sep 2004
    Posts
    6
    To those whov've been such a good help to me in this forum, I just posted a new related question in the Residential HVAC forum. I posted it there because it seemed to me like it belonged there logically, but if any of you who've been tracking with my problem would be willing to take a look at it, I'd greatly appreciate it. I'm not reposting it here, because I understand that to be bad forum etiquette.

    The subject is 'Plenum Box Necessary'

    Thanks.

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