Proper Flex Duct Installation

[sunbay ac]

I am having a discussion with another AC company. My installers use panduit straps on both the inside and outside of R-6 flex duct at the register boxes. Is this proper?

[old yeller]

You bet- 2 on each, for good measure.

Inside WITH mastic to seal the pressure, outside to close off the vapor barrier so that moist air will not come into contact with the thin inner lining and condense and rot the insulation.

[vern p]

Sorry but it all depends. Read the mfg. installation instructions on the box or inside the box. Everyone i've seen says on the joints, closures and terminations to use 2 wraps of UL 181-B Duct tape and its your choice on using straps. This is on the outer vapor barrier of course. Watch those instructions cause they are changing before March 05 to include ribs on all collars and end fittings so the helix can go over the rib and be strapped and the non-metalic straps most use will have to bear a UL label. When the mfg. puts it on the box thats when you'll have to comply with that also.
Always the best advise is read the manufacturers instructions first and follow them.

[air of honesty]

The manufacturer's written instructions can be used to trump a local code only if the code is incorrect as applied to that product. Times have changed, and most inspecting authorities are gravely concerned with duct loss and energy efficiency. Both mastic and 13 SEER have been mandatory where I live for several years. No question both are superior to previous practices. I couldn't possibly pass an inspection using duct tape before applying mastic. The mastic IS the seal.

As to what's packed in the box, I can't begin to count the number of times I got a new part with the old literature. It seems they want to use up all the 'old stuff' before they print things that match the 'new stuff'.

Anyone seen a manufacturer's instructions quoting mastic yet?

[dallasbill]

QuietFlex specifies mastic on their spec sheet. We are using it now and my GC had to clue in the HVAC sub's installers.

They ripped and started re-doing it today.

[Steve Wiggins]

Panduit straps should only be used on the outer vapor barrier. If you use one on the inner liner it can be loosened by tightening the outer one.

I realize the code says to do it that way but they are wrong.

[air of honesty]

Don't overlay them on top of each other...

Set the inner just below the rib on the collar, tighten the outer till snug, with gun still on, drive it into the mastic around the collar at the plenum and cinch. No prob...

[Steve Wiggins]

Lets put a magnifying glass on the duct connection but ignore the leaky boot boxes that you can see through the cracks & corners of.

Hey I've got an idea. Me and the inspector can argue about the tape while an illegal guy isn't following any of the rules, not pulling permits or anything one block over. Its like the police pulling you over for not using your turn signal when he could be out catching real criminals.

http://www.achrnews.com/CDA/ArticleI...nalNews_Item/1,6084,128736-South,00.html

[air of honesty]

I've been waiting for a bucket that was under development: extruded plastic with external foam insulation. Nary a leak.

For a long time I painted every seam on every bucket and collar before installing. Hard to compete with that kind of labor. Quit worrying about it so much when I started putting fresh air on every system.

[Reliant Air]

In Florida all joints have to be mechanically fastened independent of the closure system. Around here they interpret that as a panduit is the mechanical fastener and the tape is the closure system.

http://www.sbcci.org/Florida_Buildin...0sec%20603.pdf

see 603.1.1 for mechanical fastener requirement.

see 603.5.6.1 for approved closure systems for the inner liner of flexible ducts

of course there are other ways to mechanically fasten the inner liner but the panduit is probably the easiest.

[cde72]

I have seen it done completly with tape, and it kinda looks impressive, until you go back 6 months later and its falling apart... If we are talking flex duct to collars, I like painting the collar with mastic, slipping the liner over it and using 2-3 sheed metal screws to hold the wire down, hence, holding the inner liner in place, this is before the damper lever, then I slid the insulation up over the lever, flush with the trunk and use 2 panduits, both after the lever... Any problems with this???

[Steve Wiggins]

You use sheet metal screws on the inner liner of a flex duct?

If you are using two panduit straps you must be buying the wrong brand. Some suppliers in our industry are the equivilent to Harbor Freight quality.