How to detect slight air movement?


Other than smoke and toilet tissue, are there other ways to detect slight air movement?
The problem with smoke (I used an incense) is that it works great detecting horizontal or strong downward air movement, but not so good detecting weak, vertical air movement since the smoke rises up anyway.
Toilet tissue works well detecting upward air movement, but needs stronger air to cause any visible movement.
I need to do this after I hired a contractor to seal my HVAC ducts in the crawlspace. I want to show them the ducts are not 100% sealed by turning on all ventilation fans in my house (to create a vacuum effect inside), and showing them there is air coming out of all floor registers. Although I am able to cause slight movement with the toilet tissue test, I like something with stronger indication.
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Perhaps you could still use smoke by showing the differential between how fast the smoke rises over the registers vs. away from the registers.
Build a funnel over the register so that the air movement is forced out of small opening. Hold your smoker near the opening and then over it. You should see an increase in upward movement over the opening.
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james wrote:

Hot-wire anemometer works well at low velocity. Close all but one vent and block the return to make all the air come out one vent.
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Take a few different kinds of plastic shopping bags, and stretch out a sample of the plastic to the breaking point.
Chances are that at least one will produce an ultrathin piece of plastic that will readily move with the slightest breeze.
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By creating a negative pressure (vacuum) in your house, air can still enter thru wall sockets, furnace intake and vent, hot water heater vent, plumbing vents, bathroom fans and every nook and cranny. I doubt your floor registers are air tight either.
I don't see how you could prove he didn't do the job by the method you describe. It would be amost impossible to make duct work air tight.
Hank
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Take a piece of cotton string or light cord. Light it on fire. Blow it out. It will smolder and give off a wisp of smoke for a long time. That is easily affected by any air motion. Even the minutest. Great to put by windows to see if air is being sucked out or blown in. Leaves a slight smoke smell, but it goes away quickly.
Yer welcome.
Steve
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"Other than smoke" was the first three words of the OP.
Fail.
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wrote:

"Other than smoke" was the first three words of the OP.
Fail.
So, what happens now? I should think that the OP would simply disregard my post, and go on. Others who may be considering doing such a thing might take a bit of useful information for future reference. Still others who don't really care would just ignore me and the post. Which is the logical thing to do.
Now, it comes down to you. I'm sorry, but the position of Netnanny in this group is taken by at least a dozen people who have been here longer than you. Should you like to apply for the position, please feel free to do so, just know that it will be a long long time until such position is available. It pays nothing, but it does give tremendous satisfaction to the obsessive and anal, which sounds like you.
Steve
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You could learn from your mistakes and actually read posts before responding to them.
Or you could forge ahead, toss out an insult, and continue to embarrass yourself in the future while degrading the content here.
It's not a tough choice (usually).
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On Thu, 4 Feb 2010 16:28:15 -0800 (PST), mike
movement?:

Ditto
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True. However, if you had kept reading you would see that the OP went on to explain why he didn't think smoke would work and Steve offered a different way of using it that might.
Now I'm going to really tick you off by not making any attempt to answer the OP's question but rather ask why he thinks this air movement matters if it's so slight that he's having trouble finding a way to detect it?
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Hey! I offered a different way of using smoke and nobody yelled at me.
I'm feeling left out.
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Hustlin' Hank wrote:

That's what I was thinking. If it's this difficult to show where the air leaks are, it must be pretty damn airtight already! Hell, if you want the whole system hermetically sealed, you're going to pay a lot more.
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I think you're discounting smoke too quickly.
Sure, with smoke generated from a flame, it does rise. But now a days there are numerous devices that generate a cold smoke, smoke that doesnt rise.
Just google for smoke pen or smoke pencil.
There are two types in particular. One is based on finely powdered silicon dioxide, the other is based on titanium tetrachloride.
You're not going to beat the sensitivity of smoke.
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wrote:

buy some stick incense.At least it will smell nice.
--
Jim Yanik
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line 2... "(I used an incense) "
Good idea. :)
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james wrote:

Talcum powder or corn starch works. There's also a fine powder sold to bowhunters used to discern slight wind movement, you might ask your local bowhunting shop if they carry it.
A quick giggle search brings up the following:
http://www.bowhunting.com/shopping/Products/Alpine-Super-Duster-Wind-Checker__500.aspx
Jon
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There are candles of soome kind that will send smoke into a system that you want to check for leaks. Something like that was used in our fumehood system at work years ago to check for leaks in the system from our hoods onwards. I would assume that HVAC companies would know more about it.
--
Best regards
Han
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