Proper way to connect flex to metal plenum?

Greg__RJuly 9, 2012

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.


Thank you for reporting this comment. Undo

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.

    Bookmark   July 9, 2012 at 4:34PM
Thank you for reporting this comment. Undo

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?).

    Bookmark   July 9, 2012 at 4:50PM
Thank you for reporting this comment. Undo

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

    Bookmark   July 9, 2012 at 5:34PM
Thank you for reporting this comment. Undo

and last.

    Bookmark   July 9, 2012 at 5:40PM
Sign Up to comment
More Discussions
Thoughts on proposed HVAC system?
To start: my house is two-level (main plus upper)...
Opinions please Mitsubishi M - S E R I E S H I G H P E R F O R M A N C
Our HVAC guy is suggesting this for a complete system...
Honeywell th6320R Thermostat
My Honeywell TH6320R thermostat (communicating with...
company insists on all payment in advance
Having 2 mini-splits installed, have already paid half...
Replacing heat pump and keeping current air handler....
Well the good news is we are being blessed with a new...
Sponsored Products
Serena & Lily La Jolla Basket
Serena & Lily
Haverhill Wall Sconce by Hudson Valley Lighting
$268.00 | Lumens
Promenade Dining Armchair in Red
$89.00 | LexMod
Henge Ash Blue Wallpaper R1425, double roll
Walls Republic
Pastel Dupont Desk in Walnut
Beyond Stores
Area Rug: Fun Time Exotic Creatures Multi Colored 39" x 58"
$49.97 | Home Depot
Calligaris | New York Swivel Stool - Quick Ship
Milton Flemish Brass One-Light Bath Fixture
$192.00 | Bellacor
© 2015 Houzz Inc. Houzz® The new way to design your home™