I did an audit yesterday and found out that a single doggy door was responsible for 1,300 CFM50 of air leakage (in an already-leaky house...total leakage of 5,300 CFM50 and only 2,200 square feet of conditioned floor area).
So, what to do about this doggy door? I could spent some time thinking of a clever way to address this, or do some research online, but I thought of y'all first, as the preeminent professionals.
Replace it with one that has two doors (one on each side) & magnets - they work great
I can't recall the brand but the last few I got were at Home Depot & I think I even saw them at Lowe's
Most pet flaps have some sort of positive closure, magnet or similar, and for the most part they work OK, although some air works its way around the flap's perimeter.
What I think happened here is that the blower door test pressure, which far exceeds natural pressure, overwhelmed the flap's magnet and it swung open, allowing an extra 1300 CFM. That should not occur under normal, non-blower-door test conditions.
Let me call Bull - if the blower door could pull it open, that means the wind will easily blow it open as it wasn't able to resist one pound of pressure (PSF) --- for more see Pascals & Pressure
Either the magnet is shot, it is filthy, or the unit is worthless, which is one reason why I like the double flap system
I appreciate the frankness Sean (I really do).
Let me look into this flap again, and maybe these folks are looking at the POS series pet flap.
The blower door test pressure of 50 Pa is roughly equivalent to a 20 mph wind, which is quite uncommon in most areas
Unless you live in Oklahoma.
I have to look at this flap again. It appeared to fit by friction.
Locating Doggie Doors on South or East walls helps a lot.
worry more about the other 4000 cfm
the air coming from the dog door is fresh air
Where is the other 4000 cfm coming from?
I recently had a similar situation, only the doggy door was big enough for an adolescent to crawl through. When I told my client she should consider replacing the door, she waxed nostalgic about the happy times when her dog and children would chase each other through the door. She made it clear she'd never replace the thing. I still haven't done any work for her.
Another trick I've seen is to dedicate the bottom half of a cabinet as a vestibule/mud-room with a second air-lock flapper like Peter suggests. Obviously you'ed need to design some people access to clean it out occasionally, but I agree with Glen re. the other 4000 cfm.