Testing for "spillage" of combustion gases means making sure the bad stuff that's supposed to go UP the chimney doesn't come back DOWN. It's a critical part of home performance analysis, according to BPI, RESNET, and everyone else. If you don't know what it looks like, you might feel a little lost- let your old pal Corbett the diagnostics guy show you the single most awesome example of what you shouldn't see in your clients' homes!
Visit an attic (vicariously) with building performance expert Corbett Lunsford to find a tiny problem that may force us to replace the floor and ceiling of this building- and it might happen to you someday too! Stop guessing- Proof Is Possible. Get up in that attic and have a look!