Positive or Negative?


I have a cabin, and this trip, it was COLD up there. I noticed several major air leaks, which I addressed with gaskets, wiper gaskets, and weatherstripping.
I saw a program once where they used smoke to detect leaks. They had IIRC a piece of cotton rope that gave out a wisp of smoke, and this wisp followed any air flow.
Would I put a good sized fan outside blowing in to create positive pressure inside, or put it exhausting out to create negative pressure in order to follow the wisps of smoke and see where to chink and caulk?
Thanks in advance
Steve
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Steve B wrote:

Google smoke pencil. The fan is inserted in the doorway/window blowing out so the smoke gets drawn into the building. If you need to use a fan you have a pretty tight cabin.
R
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Steve B spake thus:

My guess is you'd have better luck blowing in from the outside. It would be more work; you'd have to aim the fan where you suspect there might be a leak, then check it on the inside. But putting the fan inside would likely cause so much turbulence it'd be hard to tell whether the smoke wisps were being blown by the fan or by a leak.
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David Nebenzahl wrote:

Actually I would have guessed "blowing in" for a blower door test but.............
http://www.eere.energy.gov/consumer/your_home/energy_audits/index.cfm/mytopic190
shows blowing out to create negative pressure in the house....also gives some prep tips
'cheers Bob
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Exhaust out, on a cool day. Put a $65 Kestrel 1000 air velocity meter in a partially opened hallway window and open and close some doors to rooms to find out where to airseal first, and watch the incoming air velocity increase as you seal up leaks.
Nick
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Google is your friend. I googled this up. You overpressure the house, and then the smoke will flow right towards the leak. It showed a blower that goes into a window space.
I looked at smoke pens, and boy, are they expensive. I think I will use a cotton cord, or dig out some of the Patchouli incense sticks left over from the hippie years.
Steve
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Apparently your friend Google is putting you on. The way you mentioned is contrary to the standard procedure, and for several reasons. This is the standard way, and the US DOE isn't known for pulling your leg. http://www.eere.energy.gov/consumer/your_home/energy_audits/index.cfm/mytopic190
If you use a small fan it won't have as much effect in the far reaches of the house, so generally they use very powerful fans which would drag in a lot of undesired stuff along with the desired air pressure differential and blow your stuff all over the place. Think dust storm. If the house is put under negative pressure, all of those little gaps and cracks work essentially as a filter to keep out most of the undesired dust, pollen, etc.
Also think how the smoke is used in detecting the leaks. In your scenario you can't hold the pencil right up against the suspected area surface because the smoke movement wouldn't be as noticeable traveling just a fraction of an inch. If the air is being sucked in to the house the smoke travels inwards and there's a nice smoke plume.

There are definite advantages to the smoke pencils, pens, bulbs, ampules and other dedicated devices. The pencil smoke is lighter and is a more sensitive test and it won't stink up your house. There are cheaper alternatives such as http://www.metermall.com/product%20pages/Smoke/Smoke%20Emitters.htm , but even if you buy a pencil that costs 50 bucks, you could sell it on eBay when you're done with it and get most of your money back. Think of the higher initial cost as a refundable rental deposit. Google seems to be messing around with you today. ;)
R
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If the air is being sucked in to the house

Now, I'm confused. If air is being sucked into the house from outside, wouldn't the pressure inside be greater, and the plume go towards the leak? Wouldn't the fan have to be sucking air out of the house in order for the smoke to travel inwards?
I guess it's this simple:
Do you want the smoke to blow towards you, or have it blow towards the leak?
Even on Google, I found directions stating to do it both ways.
Steve
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Steve B wrote:

Sorry. I should have made that sentence clearer. The fan is indeed sucking air out of the house, and the leaks are allowing air to be sucked in through them.

It's preferable to have the house in negative pressure as that is how the air leaks work. Air infiltration, just as the name implies, is unwanted air entering the building. So to recreate the leaks at an amplified rate to make it easier to detect them, the house should be in negative pressure with the fan sucking the air out of the house.

That's why Google, while being your friend, also hits on your girlfriend sometimes. Never turn your back on Google.
R
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Steve B wrote:

Typically the blower door tests measure the flow rate to depressurize the structure by 50 pa
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If there's an attic hatch or the likes, maybe just open that (hot air rises).. .and then do a walkaround the walls, doors, windows etc with that smoke stick, rope, joint ... whatever :-)
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If there's an attic hatch or the likes, maybe just open that (hot air rises).. .and then do a walkaround the walls, doors, windows etc with that smoke stick, rope, joint ... whatever :-)
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Heck, I did a walkaround when it was 9 degrees outside, and I could feel drafts. In some places along side the beams, I could actually see daylight. This is going to be quite a long process, probably starting with the biggest leaks and working back from there. Good news is that the way this was rough finished, it is easy to pull off the trim pieces to get where I believe most of the gaps are. Then just renail the strips, or even perhaps put some better looking trim instead of the rough one by's.
Steve
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Under "see daylight" you might appreciate this story. This summer a buddy decided time to refinish the cabin. Figured he'd save some time, picked up a power washer, and ... well ... was his wife pissed when she came home and did that walkaround inside the cabin.
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Dunno if this is useful, but I find those plastic grocery bags pack very nicely into cracks and crannies stopping drafts. Just use a trowel, putty knife ... probably an ordinary kitchen knife would be ideal ... to work them in.
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twisted up all tight, and light it. (Shove it in a pipe if you want to more closely simulate installed conditions) Most cheap plastic like that supports flame real well, and can wick it into crevices.
aem sends...
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