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Blower door testing with IR thermometer or smoke stick

Can I rely on using only an IR camera during a blower door test to find air leaks in the building envelope of a very tight new construction home?

We will be conduction our first of planned 2 or 3 blower door tests to achieve the Passive House standard of 0.6 ACH@50 in southern Maine. This first test will be done with the building envelop completed, windows and doors installed, air sealed all gaps, but before plumbing, electrical, insulation etc trades begin work.

Blower door testers I have spoken to in the area use one or more detection tools: IR thermometers, IR cameras, and smoke sticks. Others use only the IR camera. Is one tool better than the other? If we use only the IR camera, do we have to heat the interior with a propane/kerosene space heater to raise the interior temp sufficiently to spot the air leaks. I have personally done nearly all the air sealing as construction has progressed, so I don't expect to find any large or medium holes, but more likely just smaller holes.

Asked by Roger Normand
Posted Jan 25, 2013 11:23 PM ET


11 Answers

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I'm a smoke fan, and do not yet own an IR (but one is on the shopping list...) Those things said:

Smoke is cheap and works in any condition of temperature, while IR requires a temperature differential for detection.

IR INFERS air leaks from the heat transfer that arises from the leaking hot (or cold) air, an indirect effect. Smoke travels WITH the leaking air.

In your shoes, particularly since you are striving for a very tight house, I would fill the interior with smoke and then pressurize it, then watch for smoke leaking outside. Smoke is most easily seen on sunny days with minimal wind.

Both IR and smoke should be in the arsenal of a tester, particularly in the case of a PH project, IMO.

Answered by Curt Kinder
Posted Jan 26, 2013 12:47 AM ET


I would say no, you can't rely on ONLY an IR camera to find air leaks. Yes, you would need to heat the building. I would use depressurization.

If air leaks straight in through a gap, and doesn't convectively cool a warm surface as it passes by, IR won't help. An example might be two studs that are nailed together to form a post. If air comes in between them, it will be hard to find with IR. That said, I think there is a lot of value in IR for leak-chasing, and I always use it.

Personally, I don't use a smoke stick much, but it's OK for checking for small leaks. I find that my hands are plenty sensitive, and I can find leaks easily if I can put a hand or a few fingers in front of them. Smoke sticks are highly effective if you are using pressurization and want to see where air is being sucked out. You can't see those spots with IR or feel them with fingers, but you can sure watch smoke shooting into a crack.

In your case, a very effective tool might be a theatrical smoke machine, as Curt says. You can use it from inside or outside. You would need one person to blow the smoke, and another to spot the leak from the other side of the wall. Any of your potential analysts have such a thing?

And, you don't need to use a blower door all day to find and seal leaks, you can rig up a fan to make the pressure differential instead of paying someone to run their test equipment.

Answered by David Meiland
Posted Jan 26, 2013 1:51 AM ET


A theatrical fog machine costs between $30 and $400. An IR camera costs $5,000 to $10,000.

My vote: use the theatrical fog machine. More information here: Pinpointing Leaks With a Fog Machine .

Answered by Martin Holladay
Posted Jan 26, 2013 7:12 AM ET


Thank you. Good insight. The home is about 2,200 SF on each of two levels. The crew was going to start putting up the siding, but I will ask that they halt that until we do the test. I will also look to see if we can rent a smoke machine, either at a tool rental or a party store.

Answered by Roger Normand
Posted Jan 28, 2013 10:50 AM ET


I use my hands and to reach high spots that I can't reach - a feather duster. This works pretty well.
An IR camera can work as well, but it does have to be cold outside and warm in.

My experience has shown that in passive house tight buildings the velocity that theatrical smoke machines blows out smoke, makes it worthless to find small leaks.

Smoke pencil can work to visualize leaks though...

Answered by floris keverling buisman
Posted Jan 28, 2013 4:03 PM ET


An IR camera costs $5,000 to $10,000

True, but only the first time you use it--the rest of the time, it's almost free.

Answered by David Meiland
Posted Jan 28, 2013 5:51 PM ET


We've had pretty good success with this method- we rent two duct blasters (approx 2,000 CFM each) and hook them up like a blower door to depressurize the building. With such high pressure, somewhere around 200 Pa, any leaks can be easily heard from outside the building or felt on the inside. Works well, plus it's fun. Here's a video from one of our projects: http://www.youtube.com/watch?v=Q1XEpXKbT5c

Answered by Robert Hawthorne
Posted Jan 29, 2013 12:04 AM ET


Two duct blasters? Why not just use one blower door?

Answered by David Meiland
Posted Jan 29, 2013 2:24 AM ET


Low-end imagers from flir.com or Extech are more like $1000
these days -- is there any reason to avoid those and go higher
end if you don't need high resolution? It's on my tentative
shopping list too, but would welcome any war stories first.

You have to be careful with theatrical fog. I've used it for
... well, theatre, and it tends to leave a film of goop behind
once it's landed on things in the fogged space. It's not
nearly as bad as in the old days when the fog fluid was oil-based,
but it's still a mix of water and glycerine and some of the
mixtures don't evaporate away as readily as you think. Probably
fine during construction, but you don't want to waltz into
someone's finely-appointed living room and blast away.

I agree that an imaged cold spot is not necessarily an air leak;
you have to get close and check. Hands are good, and for even
greater sensitivity to temp differences and flow I've found
that lips are even better. I guess for some reason we're wired
to be really discerning about thermal characteristics of what
we're about to eat, or something. Explaining to clients why
you're kissing their walls might be another matter...


Answered by Hobbit _
Posted Jan 29, 2013 11:50 AM ET


More pressure = easier to find leaks.

Answered by Robert Hawthorne
Posted Jan 29, 2013 11:55 AM ET


Robert, two duct blasters might give you 2000 CFM each, but a typical blower door should get you more than 5000. I mean, if you really want to break the windows and rip up the subfloor...

Answered by David Meiland
Posted Jan 29, 2013 5:25 PM ET

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