Narrowing HVAC Ductwork


Old 10-21-02, 09:03 PM
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Narrowing HVAC Ductwork


I have a 7 foot ceiling in the basement being finished. The main duct trunk is 10 inches wide by 8 inches tall. I want to replace this with a narrower main trunk to give me as much extra head room as possible. This will mean replacing most of the runs as well right? There will be six runs off this main line (none new, just moved a bit). How narrow can I take it? The return duct in this part of the basement is not an issue.

I have found VERY LITTLE information on how to do this kind of project yourself. It seems like it should be reasonable easy to but there seems to be little DIY info on the subject. Any help on this would be fantastic.

Also, with a little job like this...replacing six runs plus a new narrower main trunk in a one floor rambler with a wide open basement, how much should I expect a contractor to charge for this kind of work? Will I save much money by tearing out the old stuff myself?

Thanks for the help.
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Old 10-22-02, 01:24 AM
lynn comstock
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Look at this information for a good start.

Round is the best shape for a duct. Square is next. The flatter and wider it is the more friction there is and the duct area must get bigger. A ratio of 4 to 1 is the flattest recommended ratio.

Also look at

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