Return to the Heating & Air Conditioning Forum | Post a Follow-Up

Proper way to connect flex to metal plenum?

Posted by Greg__R (My Page) on
Mon, Jul 9, 12 at 14:39

What is the correct method for connecting flex duct (R-8) to a metal plenum? Mine were taped in place (metal duct tape) and my air handler has blown them off the metal flange. Should these be screwed in + the tape? The flex duct doesn't seem to have much to screw into.

Also, is a big zip tie OK to hold the insulation in place?

We had our duct work replaced due to flooding last year and one of the connections has broken. I want to bring the company out to fix the problem but want to know the correct way to install so I can ensure a correct fix.


Follow-Up Postings:

RE: Proper way to connect flex to metal plenum?

start collar mastic sealed to plenum.
inner liner mastic sealed to start collar.
insulation jacket and insulation brought in
contact with plenum. mastic sealed insulation
jacket to plenum.
lock ties are often used to hole insulation
jacket and insulation in place.

either paint on mastic or mastic tape can be used.
paint on mastic takes longer, as mastic has
to dry.
mastic tape is more expensive, but good long
lasting seal. because it doesn't have to
dry, it goes quicker.

I use Hardcast brand 1402 mastic tape.
silver with sticky gray (mastic) backing.
costs about $30. per roll at hvac supply.

foil tapes are not strong enough. just like
duct tapes, they fail quickly in extreme attic

best of luck.

RE: Proper way to connect flex to metal plenum?

Looking @ it closer, I see a gray sticky material on the inside of the flex and the tape has a grey sticky backing (tape is metallic). It looks like they used the right materials but for some reason the duct still fell off (metal was dusty?).

RE: Proper way to connect flex to metal plenum?

inner liner connected to supply box,
same install for plenum install
don't know how to do multiple pics
so outer liner pic to follow

RE: Proper way to connect flex to metal plenum?

and last.

 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!

Return to the Heating & Air Conditioning Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Please review our Rules of Play before posting.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.

Learn more about in-text links on this page here