HVAC Flex Duct Disconnect/Clamp Shut?

[Digital2k2]

I've been thinking about disconnecting two 6" flex ducts from the HVAC supply line that are a few feet apart. If I went that route, I was thinking of screwing a piece of matal slightly larger than the ducts onto the supply line to seal it up. I could use metal duct tape for the edges.

Another thought was to clamp the ducts completely flat within a few feet of where they are attached to the supply line. I'm still not sure what would be best to use for clamping them, or if it would seal them off completely that way. Either way I want to have the option to use them again in the future if I decide to condition the sunroom again.

For the past few years, I have had the louvers in the ends of them shut, but enough air gets through that I have to leave the sunroom door cracked so there isn't a large negative pressure issue (just two supply ducts in there, no return).


Has anyone heard of or done either of the methods I'm thinking about to completely seal off/disconnect the ductwork for that room?

 

[Fsharp]

When you take off the flex duct their will be a collar that it connects to. Buy a duct cap that is the same size as the collar, pop it on and seal the edges with metal duct tape.

Don't clamp the flex pipe, you may bend the coil spring that keeps it open or tear the inner lining.

An alternative to all this is tape over the registers in your sunroom to shut them completely off.

 

[EA82]

If you dont have duct board to cap off where you are disconnecting the duct I would just cut off the flex duct about a foot from the plenum and pinch it shut, that way at least it is insulated. If you just put metal and tape it may condensate during the hot months if the air handler is located in the attic.
Or just get some insulation from the duct you are disconnecting and tape it on the metal cap, lots of tape is the idea if you don't have spray glue and mastic.

 

[Digital2k2]

Didn't know about duct caps, thanks for mentioning! I'll definitely go that route over clamping the ductwork. One reason I wanted to cut it off at the supply is that the ductwork under the sunroom is open to the elements. I'm afraid if I completely block off the registers, it may leak at its connection there and pump conditioned air outside.

The supply line is in the crawl space that's encapsulated and dehumidified, so capping it there seems a lot more efficient. Any ideas on what to stuff/seal the disconnected flex ducts with to keep them clean and from pulling air out of crawlspace?

Another thought is if it's that smart to completely close off the sunroom. Since it's a good 5ft off the ground and completely open underneath with surrounding deck (used to be a screened in porch), there's no moisture concern from underneath or any other source. If I allow it to sit at extreme temps in the Summer I'm a little concerned about mold in there even without sources of added moisture...

 

[EA82]

I think you are getting supply and return mixed up, return is the intake and supply is the hot/cold air discharge. I think you are trying to seal off 2 returns. Just put lots of foil tape and squeegee it good, i think you may also find (mastic) at home depot which is a duct sealant, you apply it wet over the foil tape and it dries hard like cast.

 

[SHOZ]

I've done this on a couple runs. I just stiff fiberglass insulation in the duct.