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Balancing Negative Pressure

suect | Posted in General Questions on

Are there options to balance negative pressure?

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  1. walta100 | | #1

    Have you had a blower door test as part of and energy audit? When it gets cold this winter have your energy auditor visit with his inferred camera. It sounds like the camera will help you understand why some rooms are colder than others. Maybe you will show you are missing insulation or have huge air leaks.

    Is your duct work in the attic?


  2. Expert Member
    BILL WICHERS | | #2

    Negative pressure is usually caused by one of two things:
    1- Too much air being exhausted from the home and not enough makeup air entering. This is the case if you have a range hood (for example) running in a very tight home.
    2- Extreme stack effect at work, which is usually due to a very leaky upper level ceiling.

    In the case of #1, your preferred option would be to either adjust dampers (in the case of unequal outdoor makeup air issues with an HVAC system) to get things balanced, or to provide a source of makeup air (in the case of a range hood, or an induced draft gas appliance). The solution really depends on the cause of the problem here, so it's difficult to provide specific guidance.

    In the case of #2, the solution is typically better air sealing of the upper level, which is probably leakier than the lower level if you're seeing NEGATIVE indoor air pressure. Usual offenders are attic hatches and recessed cans. I'd also check for leaky windows. Bathroom exhaust fans with missing or flaky dampers can also contribute. That stuff is the 'low hanging fruit', after you've addressed those things, the other things get more difficult and also represent less bang for your buck.

    Note that if you have mechanicals in the attic as Walta mentioned, that's quite a can of worms right there, since you can have a LOT of things that need to be sealed to deal with that.

    A blower door test will help to localize air leaks, but I'd try the easy "usual offenders" I mentioned earlier, since they're relatively easy to address and offer a lot of improvement for minimal effort. If you still have problems after that, a blower door test may be in order.


  3. 1869farmhouse | | #3

    Agree with the above. Assuming the cause is air leakage/stack effect and not overzealous exhaust, I can say that by personal testament, a LOT can be done with simple tools and a time commitment. Air sealing seems to be dollar for dollar one of the best things a typical home owner can do to improve their home.

  4. suect | | #4

    Thank you all for your replies.

    About 5 years ago we hired a company to air seal the areas of the attic that could be done. (We have cathedral ceilings in the great room, sunroom, master bedroom and kitchen eating area. Additional insulation was added to the sealed areas.

    We have a basement where the HVAC, HRV are located. All ductwork was sealed as best as it can be. The returns are not ducted, space cavities with cardboard panning was used. The panning was sealed with foil HVAC tape as well as the HVAC unit.

    The rim joist has fiber glass insulation but there is an outline of foam sealant in all four corners of each section.

    New Marvin clad casement windows were installed. 3 years ago.

    It feels like every time the system or just the fan turns on, hot air is being pulled in from the attic, fireplaces etc,

    I’m seeing gaps in the wood of our newer windows, rippling of the dry wall ceiling, and shadows on the exterior wall where the ceiling and wall meet.

    The HVAC system is 9 months old. We were advised to run the fan and HRV 24/7 but it is having a negative affect on the home so the HRV is on 20 min per hour and fan is circulating at 12 min per hour.

    The one item I had brought up is our fresh air intake actually connects to the cardboard panning inches from a cold air return. This is a 6” insulated flexible duct that is about 8 ft prior to connecting into the floor cavity cover by panning.

    The HRV has a 6” flexible duct for intake and exhaust but it Y’s into a 6” external duct (this duct system allows for 1/2 to be for intake and 1/2 for exhaust).

    We have done a lot to improve our home. I believe this problem was present before all we have done but I’m not sure if the negative pressure has improved by much.

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