Flip the blower door?
How often are home *pressurization* tests done? The usual
blower-door run seems to be the "suck" test, looking for cold
air coming in, but it may not tell the whole story. Turning the
fan around seems to be a logical part of a "fog test", but one
doesn't necessarily want to blast fog juice all over an occupied
dwelling as even the most benign water-based formulations still
leave behind *some* sort of residue.
I'd opt for simply using warm air as my indicator. Tonight
I ran a "blow" test on my place, using my window-fan lashup
that's good for about 20 Pa, and let it go for about half an
hour before going around the exterior with the IR cam. This
needed a cold and *calm* night, so breeze wouldn't take
away any region of air exfiltration and cool it back down.
What I wanted to look for was anywhere that might be letting
air escape, particularly in the upper reaches where stack
effect would generally have air moving out and not in, and
figured that deliberately compressing my warm air out would
reveal such issues much more profoundly and also around the
lower levels of the house. I gave things plenty of time to
settle so if, say, something was leaking inside the soffit
space or through the foundation it would have time to create
a visible heat blob.
Possibly the most revealing thing was a tiny hot spot under
the siding, corresponding to a location at an obscure end
of a kneewall space that I had seen going a little cold during
the "suck" test. This made it obvious that it was most likely
where a Headlok screw had been put through the foam and then
removed for some reason, possibly a stud miss, and then never
taped over. [pic below.] I couldn't see that with the same
precision from inside, where incoming air got baffled by
intervening structure and just caused a generally cold bay.
Maybe when it's not quite as dark and cold I'll zip open some
siding and actually figure out where that hole is.
The windows looked different under this scenario, warmer around
the ends of the meeting rail and downward -- which I'd completely
expect from knowing there's likely still a little leakage there
despite having shot globs of caulk into the most obvious gaps in
This also turned up minor issues around a couple of panned-joist
ducts running to the exterior walls, where the sill sprayfoam job
had to skip over bays. Time to pull the grilles and see what I
can do down the hole inside.
I was happy to find that the fan didn't actually move a whole
lot of cold air in; the heat didn't cycle any more than usual
over the whole hour-plus I was doing this.
Posted Mon, 03/24/2014 - 21:55
Edited Mon, 03/24/2014 - 22:19
Other Questions in Green building techniques