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  1. #1
    Join Date
    Sep 2007
    Posts
    8

    Negative Air pressure in homes

    Hi all, new to the forums

    I'd like to discuss negative air pressure in residential homes and gain some feedback on the subject.

    Making a long story short, my girlfriends house is 60 years old and she may as well have been living in a house of swiss cheese. Spent countless hours renovating and insulating. anyhoo.

    I'm in the process of renovating her bedroom, there is a "b-vent" (think that's what it's called) gas fireplace in this room and it's cold. I didn't realize what was happening in the home til I took apart the fireplace. There was a hurricane coming down the chimney all the time. Living in edmonton, the temps can get down into the -30's and -40's. Now I realize cold air falls, so it's expected for some cold air to enter through the chimney when the fireplace is not turned on.

    I'm assuming air is venting out of this home through different orifices (gas furnace and hot water tank) and has to be balanced somehow. Hence the air being sucked down the chimney and any cracks around the home such as the windows and doors.

    As a test, I unhooked the dryer vent in the basement and forced the door trap on the outside vent open to get a fresh air intake to the basement. Air started rushing in through the vent.

    Turned on the furnace, the airflow stopped, seemed to be balanced for a bit but then air started sucking in again while the furnace was running for a few minutes.

    Checked the chimney again, airflow down the chimney stopped.

    Is it safe to assume an air exchanger would fix this problem of negative air pressure in this house? If all it takes is a fresh air intake in the basement to fix many problems in the house then it's a no brainer.

    Is there anything else that can be done to the house to balance pressure?


    Thanks

  2. #2
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    2,011
    Find and hire a professional that can do a complete blower door test on the home. They can and will identify all the air leaks in the home and give you recommendations on your priorities and safety items to be fixed or modified.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  3. #3
    Join Date
    Dec 2000
    Location
    Michigan
    Posts
    724

    Hmm What goes OUT must come IN!

    Robert you are correct in your statements. You can read my web site to further understand how a home works.
    The quality of my performance, sometimes depends on the quality of my audience.
    Imitation (Plagiarism) is the best compliment one can get -- "Open A Window"

    To improve Indoor Air Quality: Control Indoor Air QUANTITY = "I.A.Q.Q."

  4. #4
    Join Date
    Sep 2007
    Posts
    8
    I really could use something like the equalize-air product but my main concern is the extreme cold we get in the winter. I'd need some way to heat the air before it hits the furnace. We get down to -40 Celcius and colder here in the winter time and ice fog develops (where the water in the air freezes). I can't have that directly sucked into the furnace, can't be good for it.

    How can one heat the incoming air??? Is there anything on the market that could take it up a few degrees while in the intake?

  5. #5
    Join Date
    Dec 2000
    Location
    Michigan
    Posts
    724

    Smile Johnny Carson

    Mr. Carnak usually reads my posts and as he is from your area he maybe able to provide some suggestions.

    However, remember that the outside air must re-enter the home, and I believe it is more efficient to have the air enter under controlled conditions

    Good Luck
    The quality of my performance, sometimes depends on the quality of my audience.
    Imitation (Plagiarism) is the best compliment one can get -- "Open A Window"

    To improve Indoor Air Quality: Control Indoor Air QUANTITY = "I.A.Q.Q."

  6. #6
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    Robert you should ask some real HVAC professionals for the way to combat negative pressure, and make sure they tell you how much air they will flow, and how much difference that will make in your house. Ask the guy who does a blower door test on that house. I have every reason to believe Firecontrol and Carnak are two pros who will give you advice worth following.

    I am a homeowner in S. Texas and certainly not such a pro, but I can say in my house there was a blower door test done, and I would need 400+ CFM continuous to make a 2 Pascal difference. Your girlfriend's leaky house would surely be different. You do have a carbon monoxide detector or two, don't you? Find a good local pro real soon for this, I read every once in awhile about people getting into trouble (e.g. death) from backdrafting appliances. I would hate to be reading about you or your girlfriend, being lulled by buying any product which does not flow enough to do the job.

    Information from Building Sciences Corporation is a high grade source, its central guy Joseph Lstiburek is Canadian and will understand the challenges particular to your climate.
    http://www.buildingscience.com/bsc/about/default.htm
    I believe you can phone them at 978.589.5100 and talk about this.

    Best wishes -- Pstu

  7. #7
    Join Date
    Apr 2002
    Posts
    11,808
    Does the fireplace in the bedroom vent through the roof or the wall
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  8. #8
    Join Date
    Sep 2007
    Posts
    8
    Well, this is probably not the best thing to say in a professional forum but i'm still trying to undo what some of these "pro's" have done to this house. I'm really losing faith here.

    From bad window installations, to furnace ductwork updates to lack of insulation, illegal/bad/stupid plumbing. Many things were either done illegally, just plain wrong or half fast and never finished, the list is long. I don't even want to get started on electrical. I've gone through more sprayfoam and insulation than I can shake a stick at and i'm probably up to an ocean of caulking by now. Lost count of the rolls of tuck and aluminum tape. So much of this house has had to be torn apart and redone.

    I tend to use burning incense sticks to find leaks, it's a heavier smoke and works well. Did some testing the last couple of days with furnace running and not. The bathroom vents were bringing some air in (bad exhaust flaps) but the chimney was like an incoming hurricane. When I opened the dryer vent fully and left it open, air came rushing in but the rest of the vents went neutral. It's been like that for a couple of days now and there's a noticable difference in the bedroom (with the fireplace) already. Getting overnight frost here already.

    I was just thinking of an idea to warm the air coming in if I install an intake. Nothing dangerous or interfering but it should work just fine. I'll post back in the next few days if it works like I think it will

  9. #9
    Join Date
    Sep 2007
    Posts
    8
    Carnak, it's a woodburning conversion to gas, . Single pipe feeding through the original chimney.

    A friend of hers has a new gas fireplace, never installed, has both intake and exhaust. Giving for free, can't beat that price. Better system, air intake from outdoors.

  10. #10
    Join Date
    Apr 2002
    Posts
    11,808
    Homes not as old as hers but built say in the late 60s or early 70s were walking time bombs for down drafting when people started sealing them up reducing the way air would enter a home.

    Possibly your good intentions have aggravated the problem.

    I would not start arguing your opinions of pros in here else you are not going to get much help. Also be advised that this is not a DIY forum either, especially with life safety issues.

    As you suspect appliances that bring in there own combustion air are better.

    If she has a furnace with a pilot light and a drafthood or what is called a 'mid efficient' furnace, where it has a fan that pulls burnt gas through the heat exchanger and discharges to a metal chimney, then you do not want to be sucking in -40 air into your return, it will rot out the heat exchanger.

    The high efficiency furnaces, which vent with plastic pipe, can take the cold air into the return but I do not recommend this in northern alberta.

    Consider searching http://www.hrai.ca/ for a contractor in your area with some training and certification in residential ventialtion and combustion air. This really sounds like someone needs to take a look and see what is going on in your woman's place who knows what he is doing.

    Hoyme Manufacturing in Camrose has motorized combustion air intakes also.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  11. #11
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,944
    Carnak, just curious, why not use outside air in Northern Alberta? Is it because of its being too cold, and why would that be a bad thing with a condensing furnace?
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  12. #12
    Join Date
    Sep 2007
    Posts
    8
    If she has a furnace with a pilot light and a drafthood or what is called a 'mid efficient' furnace, where it has a fan that pulls burnt gas through the heat exchanger and discharges to a metal chimney, then you do not want to be sucking in -40 air into your return, it will rot out the heat exchanger.
    That's her furnace, and that's my concern. I don't want to affect the furnace in any kind of negative way. I just want to get a fresh air feed into the basement as it's solved alot of issues in testing. I need to warm said air before it hits the furnace.

    I'm not looking to argue, nor am I messing with life issues, I know my limitations here. When I first walked into this home, yeah, there were alot of life/dangerous issues. I've spent most of my teens working in renovations so i'm no stranger to it.

    I asked if an exchanger is the way to go in my original post... Is this the way to go???

  13. #13
    Join Date
    Apr 2002
    Posts
    11,808
    it shouldn't hurt the HX of a condensing furnace, just it will drive mositure into the walls

    I seen them do it in Calgary on the 80% furnaces was just asking to rot out the HX and begging to push water in the walls.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

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