I need to change out some outmoded ducting

Old 06-23-15, 04:25 PM
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I need to change out some outmoded ducting

First, thanks for your time. sometimes a bit of knowledge can save a ton of time and money. I enjoy saving both.

Our house is 2600', built in '78 in New Mexico. Originally built with a swamp cooler, later upgraded to a heat pump, later upgraded to a newer, larger heat pump. New model is a 5 ton and is 3 years old.

the problem I have is the ducting. Most of the house has standard flex to ceiling mounted vents and isnt an issue. The bedrooms (there are 4) all take air from a common hallway "box". the ceiling in the hallway is itself, a duct. each bedroom has, above the door, a vent cut through the drywall into the hallway. This "hallway box" is serviced by a 12" flex line that dumps in the top. 3 of the 4 bedrooms do Ok, IF you close off the 4th (the master suite). The long and short of it is this 12" flex line goes into an effective plenum that is 75 cubic feet. The master suite is approx 850 sq feet and is serviced by a single vent off this monster hallway box. Wife has threatened to kill me if this isnt made right, we have lived with it for a few years.

What I need to know is this: can i run that 12" flex line into a plenum box of my creation and branch off said box and run 6 or 7 smaller lines to the unserviced/underserviced areas of the house? If so, what sort of dimensions we looking at, ie box volume/shape, duct size.

Again, thank you so much for any help. You may be saving a marrage! Please feel free to PM me. I have some pics of the current state of things

Last edited by PJmax; 06-23-15 at 04:37 PM. Reason: removed email address
Old 06-23-15, 04:41 PM
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Welcome to the forums.

I can't really help you with your problem but I did remove your email address from your text. Advertising your email address opens up the can of Spam and no one wants that.

I substituted PM (private mail) for email. Go into your profile and set up your PM's to send you an email when someone responds.

The pro's will be by to assist you.
Old 06-25-15, 10:20 AM
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Branch lines should really come off of a main trunk line. This is best practice. 12in flex would normally be sized for 400CFM on supply duct.
Old 06-25-15, 10:34 AM
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We do prefer replies to be posted on the public forum, rather than by PM, so that everyone can benefit!
Old 06-25-15, 12:54 PM
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Some pic's would really help.
Old 06-25-15, 01:05 PM
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