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Old 04-27-2012, 04:03 PM   #16
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feasability of replacing AC flex ducting by myself?


A slightly better way is to use your static probes and manometer to measure the static in the return and the supply at the air handler. then use the install manual to tell you how much air it is moving. then measure how much is actually coming out of your supplies, and being taken back through your return. This will give you both total duct leakage, and tell you which is worse, return or supply.

I have seen systems that the return at the unit was getting 1600CFM, but only 1200 was being brought through the return grilles. While the supply at the air handler was putting out 1600CFM, only 1300CFM was coming out of the supply registers.

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Old 04-27-2012, 06:44 PM   #17
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feasability of replacing AC flex ducting by myself?


i think i see what you are saying, by probe i assume u mean a pitot tube? the pressure gauge i have is a dwyer 2002 magnahelic, but i dont have a pitot tube for it. i see tho how you could use a pitot to measure the static pressure at a specific part of the duct, then just calculate the flow. something tells me however we are not talking about a simple Bernoulli equation to calculate the flow rate. id have to read up some on that, been a few years since pe201,202 lol...
http://www.dwyer-inst.com/Products/P...eName=Ordering

do you think i could build a pitot tube? im thinking steel brakeline tubing or something along those lines...
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Old 04-27-2012, 09:13 PM   #18
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feasability of replacing AC flex ducting by myself?


If you have the manual for the unit. All you nee to do is check the static pressure. you wouldn't have to use a pitot tube. A pitot tube could be used, but isn't necessary. Dywer A303 static probe is all you need, and you can make it up yourself.

Using a pitot tube to measure velocity pressure, and then determine CFM. The formula would be 4005 times the sq rt of the velocity pressure divided into the sq ft of your duct work you took the vp of.

EG: a 2 sq ft duct. vp = .05, the sq rt of .5=.2236. .2236 time 4005=895.5, 895.5 times 2 sq ft equals 1791 CFM.
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Old 04-28-2012, 03:24 AM   #19
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feasability of replacing AC flex ducting by myself?


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Originally Posted by beenthere View Post
If you have the manual for the unit. All you nee to do is check the static pressure. you wouldn't have to use a pitot tube. A pitot tube could be used, but isn't necessary. Dywer A303 static probe is all you need, and you can make it up yourself.

Using a pitot tube to measure velocity pressure, and then determine CFM. The formula would be 4005 times the sq rt of the velocity pressure divided into the sq ft of your duct work you took the vp of.

EG: a 2 sq ft duct. vp = .05, the sq rt of .5=.2236. .2236 time 4005=895.5, 895.5 times 2 sq ft equals 1791 CFM.
excellent, thanks alot im ordering one of those right now.
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Old 04-29-2012, 05:42 PM   #20
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feasability of replacing AC flex ducting by myself?


i went ahead and sealed all the duct work i could find that was leaky over the weekend. i cut two small holes in the dryway and had a look around the small area that houses the plenum.

its actually not as small as i thought. i cant stand or crouch even, but i think i could crawl around, i have some leftover osb from a siding project, im thinking i could lay it over the rafters and crawl about somewhat easily.

anyway when i was putting the ductwork back together i noticed the inner part of the duct is actually like a plastic meshwork? that cant be good can it? any hole in the outer covering would mean a leak... what do you guys think about this stuff?

heres a picture.

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Old 04-29-2012, 05:48 PM   #21
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feasability of replacing AC flex ducting by myself?


Replace that duct, its garbage.
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Old 04-29-2012, 05:54 PM   #22
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feasability of replacing AC flex ducting by myself?


New code requires R-8 insulated ducts. Not certain but you may be able to purchase it yourself from Quiet Flex on Britmoore, north of Clay I believe.
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Old 04-29-2012, 05:56 PM   #23
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Replace that duct, its garbage.

I've never seen that mesh liner duct before.
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Old 04-29-2012, 06:00 PM   #24
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feasability of replacing AC flex ducting by myself?


house was built in the 70's so, im guessing builders were more caviler back then.

ill look into that store doc, thank you.
im going to wait till i get my books in tho. id like to get a good handle on what im doing first.
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Old 04-29-2012, 06:14 PM   #25
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feasability of replacing AC flex ducting by myself?


I wonder how many more of your ducts are like that ? Actually what the hell? How the hell is that a duct ...with all those holes?
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Old 04-29-2012, 06:34 PM   #26
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I've never seen that mesh liner duct before.
Only seen it a couple times. old mesh garbage.
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Old 04-29-2012, 06:58 PM   #27
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feasability of replacing AC flex ducting by myself?


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I wonder how many more of your ducts are like that ? Actually what the hell? How the hell is that a duct ...with all those holes?
pretty sure they are all like this.
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Old 04-29-2012, 07:24 PM   #28
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feasability of replacing AC flex ducting by myself?


Time to replace them!

http://www.homedepot.com/h_d1/N-5yc1...&storeId=10051

http://www.homedepot.com/Building-Ma...&storeId=10051

Have you gotten any quotes yet for replacement to see whats the cost between getting a contractor and DIY?
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Old 04-29-2012, 07:28 PM   #29
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feasability of replacing AC flex ducting by myself?


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Time to replace them!

http://www.homedepot.com/h_d1/N-5yc1...&storeId=10051

http://www.homedepot.com/Building-Ma...&storeId=10051

Have you gotten any quotes yet for replacement to see whats the cost between getting a contractor and DIY?

I'm in pretty much the same city as Q. I can tell you it's $200-$250 per individual duct run, installed.
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Old 04-29-2012, 07:28 PM   #30
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feasability of replacing AC flex ducting by myself?


i haven't actually, the people i had over last time didnt seem interested in replacing just the ductwork.

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