[Exeric]

Update on the bath fan CFM requirements... After googling I found this:

"First, determine the height of the building (H) above grade. Second, arbitrarily select a neutral pressure plane height (Hnpp) above the grade of the building, usually one or two storeys above grade in a multi-level building. In a low building select grade as the neutralpressure plane (npp).
Third, select a given height above (or below) the neutral plane, such as the roof plane. Compute the pressure difference at that plane as follows:

"ΔPs = dig(H-Hnpp)(Ti-To)/To
where ΔPs=stack effect pressure difference (Pa)
and di =density of indoor air, kg/m3
and g=gravitational acceleration, 9.81 m/s2
and H= height of plane above (or below) Npp, m
and Hnpp=height of neutral pressure plane, m
and T=absolute temperature, Kelvin
and i = indoor, o = outdoor

"For a 60-m (197 ft.), 20-storey building with a neutral pressure plane at about the 4th storey or 12 m (40 ft.) from grade, in winter with an outdoor temperature of -20°C and an indoortemperature of +20°C, the stack effect at the top of the exterior wall (and roof plane) is:

"ΔPs=dig(H-Hnpp)(Ti-To)/To
=1.2x9.81x(60-12)x[(273+20)-(273-20)]/(273-20)
=89 Pa
"
I calculated the stack effect pressure I would need to overcome by inputing the information from my house. It is 13.5 feet to the top of the roof from the floor in the house, which I'm using as the neutral plane because the floor is where the duct will vent its air. I'm using 4.44 degrees C (40 F) inside air and 29.44 C roof line air (85 F). Those are worst case scenarios with 45 F degree differential temperatures and will cause the most stack pressures that might reasonable have to be overcome after having the house unheated for a time.
Using those inputs:
=1.2x9.81x(13.5-0)x[(273+4.44)-(273+29.44)]/(273+29.44)
=18 Pa

Blower door tests are done at 50 Pa. Since I'm going to want to get a blower door test done anyway all I need to do is get that result and convert by 18/50 = .36 My understanding is that a blower door test usually gives the CFM rate within the overall air changes per hour. So when I get that CFM rate I'll multiply it by .36 to get the overall CFM rate of a bathroom fan needed to overcome the 18 Pa stack pressure. I hope I'm getting this right as I'm learning as I go.

Anyone who sees an error let me know. I'm fallible.

Edit:

Yep, I'm fallible. Used feet instead of meters. It should be
=1.2x9.81x(4.154-0)x[(273+4.44)-(273+29.44)]/(273+29.44)
=5.5 Pa

And the correction factor for my house won't be .36 but will be
= .11