Supply only fresh air & positive pressure: How much positive pressure is “too much”?
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.
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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.
To put that number in perspective, 2Pa is the pressure change you would get with a six inch change in altitude.
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.
Exactly.
Thanks!
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
Thank you!
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