1

This is in an old house with retro-fitted attic large HVAC system.

It looks like the HVAC installers just skipped over connecting an existing 4" bathroom line for some reason. The bathroom has no circulating air because of this. It is gross, hot in the summer cold in the winter, and stuffy.

There is a register/vent in the bathroom ceiling, connected to a rigid duct into the attic, which looks older than the rest of the duct work, which is all flex. But the rigid duct just kind of ends after about 6 feet. The vent-end/register is stuffed with pink insulation.

But...

There is an existing 6" flex duct that goes form the main trunk to one and only one bedroom. It goes pretty close to that existing 4" rigid duct to the bathroom that is not connected to anything.

So...

I was thinking I could just get a rigid 6" Tee, cut into the existing 6" flex and tee out to a 6" -> 4" reducer and attach that directly to the rigid 4" duct that is doing nothing.

Is this a bad idea? I don't really know what I am doing but it seems like this wouldn't be too hard to do, but I am certain I am probably missing something!

Thanks!

Improve this question
4
  • Stuffy is fixed by having air come in and go out. Adding to to duct might reduce heat/cold to the bedroom. Adding dampers to the duct work will allow tuning of heat/cold.
    – crip659
    Commented Jun 3 at 22:34
  • 5
    You're sure that 4 inch duct doesn't go to a bathroom vent fan? Those are not supposed to just terminate loose in the attic, but.. I've seen it done. And it's the right size for a bathroom vent.
    – Greg Hill
    Commented Jun 4 at 0:09
  • That’s a good point. If it isn’t though, other than diverting some air from that one bedroom, is there a reason I shouldn’t do that?
    – deef
    Commented Jun 8 at 14:16
  • @GregHill you were right! the register that is there actually has nothing attached, just a hole basically right into the attic. And that 4" duct is actually the exhaust fan venting to the attic... But can I hook up to that register? The question is still kind of the same I guess
    – deef
    Commented Jun 8 at 15:34

1 Answer 1

Reset to default
1

Yes you could try forking that existing 6" run. It's not the best solution though and there's a fair chance it'll be unsatisfactory. But it won't harm anything and it's not terribly difficult to reverse if it's not good enough. Air won't much like taking the branch out of the tee (so it'll get a small fraction of the total air flow). Use the branch to supply the bathroom so as to not overwhelm the bathroom and starve the bedroom of air flow. Better than a tee would be a wye.

Have a look at the plenum box on the output of your air handler/furnace. Is there a blank spot on one of its walls large enough to cut a 6" hole and attach your new bathroom duct there? I'd suggest choosing an area on one of the sides, ie not on the "end" relative to the axis of the air handler. The end will get higher pressure/flow and might easily be too much for a small room. A take-off from a side will get less pressure/flow. Since you're likely going to be buying a full box of insulated flex you might as well have a look at whether it'll be long enough to reach the plenum.

To attach to the plenum search online for instructions/video on how to make a "duct take off" or "start collar". There are pre-fabricated parts available for this, but you also can make one from a short piece of straight duct or from an elbow fitting.

Improve this answer

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.