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Old 02-07-2012, 07:01 AM   #1
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Duct - Flexible or Metal?


Ok guys.....yes, I did a search but did not find exactly what I was looking for.

I'm in the middle of a 2-story addition to my house. I have an existing HVAC unit in the attic of my existing house. 60K BTU system....Carrier I think...80% eff....about 4 years old....has the evap but no cond unit...don't think we will ever add it....It's California and close to the beach...unit was installed to replace the old heater in the floor toy trap....

Anyway....all of the duct in the existing attic is flexible insulated duct....I have to run one or two more ducts over to the addition...I have only one spot where I can get them into the addition...and then I have to run them down into a false ceiling in the bathroom and then up into floor joists to get the air where I want it.

Flexible or fixed metal?

And if metal, do you insulate the ducts?
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Old 02-07-2012, 07:52 AM   #2
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Duct - Flexible or Metal?


How long of a run and how many bends will it need to get where you want it?
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Old 02-07-2012, 05:56 PM   #3
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Duct - Flexible or Metal?


here is one mans opinion
http://askweldin.com/Flex.html
note that he is not a fan of flex duct.


my thoughts are that it does have its place in short runs, but its a poor subsitute for metal duct work. again, just my thoughts from my experiance.
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Old 02-08-2012, 06:50 AM   #4
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Duct - Flexible or Metal?


Quote:
Originally Posted by hvac5646 View Post
How long of a run and how many bends will it need to get where you want it?
It's about 15' and 1 bend from to the unit to the first wall...then 90 down where it needs to split into 3 different paths.

Quote:
Originally Posted by bobinphx View Post
here is one mans opinion
http://askweldin.com/Flex.html
note that he is not a fan of flex duct.


my thoughts are that it does have its place in short runs, but its a poor subsitute for metal duct work. again, just my thoughts from my experiance.
Thanks for the link....I suspect I'll be changing out some of my existing flexible ducts.....

Last question....does metal duct need to be insulated if it's inside the house? I'm assuming no.
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Old 02-08-2012, 07:13 AM   #5
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Duct - Flexible or Metal?


insulating ducts inside the envelope of the house.

some folks say no, some say yes. I know that I did, where I could and the supply air temp has very little change in it from the Rooftop unit until the farthest supply register.

My house has around 25 feet of 16 inch metal duct in the attic. I sealed with mastic and mesh every single joint. Then I taped over that, just to be sure. I then spiral wrapped the ducts in r13 insulation. Then I wrapped them again in r13. Then I covered the entire run in radiant barrier (the stuff was like heavy duty aluminum foil). A lot of my ducts are burried in the walls, but the ducts that I replaced in the walls, all got the mastic, mesh, tape and insulation treatment. I know it helped my situation as the bills have dropped about 25 percent and the comfort level in each of the rooms is now great!!

I will tell you that sealing the ducts with mastic was the one of the best things I did!!! and dont forget to seal where the ductwork comes through the walls.
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