GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Supply only fresh air & positive pressure: How much positive pressure is “too much”?

aunsafe2015 | Posted in Mechanicals on

My house has supply-only fresh air intake. I can control the amount of CFM being provided by measuring static pressure and power use, and adjusting fan speed as desired.

House is 3200 sq ft and was measured about five years back to be 4.9 ACH50.

Compliance with ASHRAE 62.2 would dictate about 70 cfm of continuous fresh air ((7.5 * 5 bedrooms) + (3200 * 0.01) = 69.5).  I like fresh air so I might actually aim for 100 cfm of continuous fresh air.

In terms of pressurizing the house, is 100 cfm a problem?  I assume not… but I’m curious, is there an accepted point that would be considered “too much” positive pressure?  For example, could I crank it up to 150 cfm if I had several overnight guests for the weekend?

Would appreciate any input in knowing how to think about this.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.

Replies

  1. Expert Member
    Akos | | #1

    A 3200sqft house (say 9' ceiling) at 5ACH leaks 2400CFM at 50Pa. So at 100CFM the pressure inside the house is:

    50Pa * (100CFM/2400CFM)=2Pa.

    That is a very small number.

    1. Expert Member
      DCcontrarian | | #2

      To put that number in perspective, 2Pa is the pressure change you would get with a six inch change in altitude.

      1. aunsafe2015 | | #5

        Hah, so the pressure change due to elevation from my 2nd story to my basement dwarfs any pressure change caused by an intake fan it would appear.

        1. Expert Member
          DCcontrarian | | #6

          Exactly.

    2. aunsafe2015 | | #4

      Thanks!

  2. Expert Member
    BILL WICHERS | | #3

    The general rule is you can't overpressurize anything with a simple fan, you would need a blower that can actually develop some pressure to have any chance of getting into trouble. You don't have anything to worry about here.

    Bill

    1. aunsafe2015 | | #8

      Thank you!

  3. Deleted | | #7

    Deleted

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |