Repost: Raising main trunk

[Jack]

I am finishing my basement. I have a main trunk running down the center of the house. It looks like it can be raised up about 4 inches to snug up against the first floor joists. I need all the headroom I can possibly get. . Can this be done? Any idea on cost (I know this is an unfair question). I am guessing I need some sort of transition boot where the duct would get cut. Would this cut air flow if a transition was put in? I don't have much HVAC experience, but it doesn't seem like this would be a huge job. . Thank you for your time.

[Edwin Pawlowski]

Yes

Can't answer without seeing it. Aside from the obvious shorten the duct on one end, lengthen the other end, there may be other factors. Anything blocking it? Pipes run over top of it?Is it rectangle or round? Any branches along the section to be raised?

[Jack]

Nothing blocking it. No pipes above it. There are flexible branches that are up in the joist space. It is a straight-shot for about 25 feet. . Edwin, I don't understand what you mean when you write 'shorten the duct on one end, lengthen the other end' . Thank you for your time.

[Edwin Pawlowski]

I was not clear there. Not the duct being raised, the ones it is attached to. If it goes up to the floor above with an elbow, the duct it connects to must be shortened. Same at the other end if it is coming from the furnace and making a turn. Depending on the setup, possibly an "S" turned piece to join the low and high parts would do. Is that what you mean by a transition piece?

[jolt]

It would be much easier to leave the duct in place and install the ceiling the height you want and cover or paint the duct to blend it in. Raising the trunk normally requires a lot of reworking to hook the runs back up to the trunk unless you home has flex duct. And if you have pipe in place it is not wise to replace it with flex duct. Installer normally try to run the trunk as close to the members as they can while still leaving enough room to get the drops and runs off the trunks. You need to look at what it will take to hook the runs and drops backup before you commit, raising the trunk isn't the difficult part. You can have a sheet metal shop or HVAC contractor come out to measure and fabricate a new transition, if properly made the static lose will be minimum. I'd be more concerned with what you might have to add in the way of fitting to reconnect the runs.

[Jack]

Yes, Edwin. That is exactly what I meant. I didn't know what it was called. Thank you again. The info you gave me was very helpful. Thanks to'jolt' as well.