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Ventilation systems and Building pressure testing questions

aston01 | Posted in General Questions on

I’ve been looking into ventilation systems/building pressures and there are a couple of areas I have struggled to find information on for residential applications.

In a home with a positive pressure balance to its ventilation system, what is considered the desired amount of positive pressure? (In commercial buildings, it appears that 0.05iwc positive pressure is common)

Where is the outside pressure tested from in a home? I could see pros & cons of a reference to outside pressure being made in an unconditioned attic, but I can’t think of a better place that isn’t subjected to wind loads.

Any clarity you can provide would be much appreciated.

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  1. nwfinch | | #1

    As an energy auditor, we needed to run combustion safety test with reference to outside pressure measurements. Since our testing was relevant to basements, in general, I would reference to outside through a basement window. If there is a bulkhead as well as an exterior door at foundation to the bulkhead; that cavity is a good wind block. Tape seams of the cracked window or door. If no window well, but the end of the manometer tube in a cup. Its a pretty quick test, and if accuracy is your game, then take a reading from all four sides of the house and average them out.

  2. walta100 | | #2

    Before you build your positive pressure system make sure to do the math unless your house is crazy tight like 0.2 ACH50 you will be pumping in large amounts of air directly from the outdoors this air will need to be conditioned to match the indoor air this is a huge energy penalty in most climates. For most people in most locations the small benefits are not justified given the huge costs.

    I agree the it sounds nice to fill your house with clean conditioned air and have the dirty air leak out the gaps and not in. Unless someone has a medical issue and you live in a very mild climate the cost benefits equation does not work.


  3. charlie_sullivan | | #3

    0.05 inch wc is 12.5 Pa, which is a lot of pressure for a residential building. Unless you have extreme air sealing, that means that you are running a supply only ventilation system. Issues to then consider:

    1. It should be adjusted to get the air flow you need, not a pressure target.

    2. Compared to a ERV ventilation system, this ventilation strategy wastes a lot of energy summer and winter. It also causes humidity problems in both seasons: In summer, you are supplying bringing in high humidity outside air rather than using the ERV to take the worst of that humidity out. Particularly on days when you don't need much cooling you could pump the inside humidity up a lot. In winter, you are pushing humid inside air through cracks in the envelope, causing moisture problems in the envelope, and, in a sufficiently cold climate, causing low indoor humidity at the same time.

    The reasons for that level of positive pressure in commercial buildings don't apply here.

  4. darusiob | | #4

    Hi there! It's great to see that you're looking into ventilation systems and building pressure testing for residential applications. These are important areas to consider when it comes to maintaining a healthy and comfortable indoor environment.

    Regarding your questions, it's true that finding specific information on residential applications can sometimes be a challenge. However, I believe this link ( ) could provide some helpful guidance on desired levels of positive pressure in homes, as well as where to test outside pressure from.

    In general, it's recommended to maintain a slight positive pressure in homes to help prevent contaminants from entering from the outside. As for testing outside pressure, a reference to outside pressure can indeed be made in an unconditioned attic, as long as it's not subject to significant wind loads.

    I hope this information helps, and good luck with your ventilation system and building pressure testing endeavors!

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