Ductwork question

**Ernie Simpson** · 08-06-2021, 06:41 AM

I have a new condo inspection coming up. My client (to be - although I've worked for her before) sent me the attached photo of the ductwork. I know that a lot (probably the majority) of ductwork installations are second (or third) rate. I did tell her that best practice is to have a solid metal duct with the flex duct take-offs of of that. In this case it is flex to flex.
Shouldn't there be an internal sleeve duct at the transition? How the heck can you properly attach flex distribution to a flex trunk? I think a lot of ductwork installers just use a lot of tape.
Comments appreciated....

Similar Threads:

**tkaiser1** · 08-06-2021, 02:18 PM

Originally Posted by Ernie Simpson

I have a new condo inspection coming up. My client (to be - although I've worked for her before) sent me the attached photo of the ductwork. I know that a lot (probably the majority) of ductwork installations are second (or third) rate. I did tell her that best practice is to have a solid metal duct with the flex duct take-offs of of that. In this case it is flex to flex.
Shouldn't there be an internal sleeve duct at the transition? How the heck can you properly attach flex distribution to a flex trunk? I think a lot of ductwork installers just use a lot of tape.
Comments appreciated....

Properly done, metal transition fittings are used in the appropriate sizes and configurations. Tees, Wyes (starting with the main size and a smaller branch duct coming off), reducers (example 10" to 8"), etc. The flex duct should have both the liner and the insulated outer section (separately) conduit strapped (think, large zip ties) to the metal fixtures. If flex duct is pulled snug enough, it will have very little additional flow loss compared to properly done rigid duct.

**Markus Keller** · 08-07-2021, 06:53 AM

The center duct looks very straight. Its probably round metal duct with an insulation sleeve around it.
If the place isn't too far away you might want to swing by there before the put up drywall to look around a bit.

**ROBERT YOUNG** · 08-12-2021, 01:05 AM

Originally Posted by Ernie Simpson

I have a new condo inspection coming up. My client (to be - although I've worked for her before) sent me the attached photo of the ductwork. I know that a lot (probably the majority) of ductwork installations are second (or third) rate. I did tell her that best practice is to have a solid metal duct with the flex duct take-offs of of that. In this case it is flex to flex.
Shouldn't there be an internal sleeve duct at the transition? How the heck can you properly attach flex distribution to a flex trunk? I think a lot of ductwork installers just use a lot of tape.
Comments appreciated....

Morning, Ernie.
Hope this post finds you and your loved ones well.
I concur with, tkaiser1.
Here are 2 notes I would include in my report.
Observation: HVAC:
1: Exterior duct insulation sleeves are not sealed with an approved duct tape at transitions.
2: Lighting circuit cable, NMD90 cable, in contact with conductive HVAC ductwork insulator.
Tell me your thoughts on my notes.
ductwork illustration.JPG

**Claude Lawrenson** · 08-14-2021, 07:21 PM

Any second thoughts about the electrical wiring? Based on what I see there's no finished ceiling at this time, but more to my point, I typically would expect to see drilled holes notched in the joist space for providing adequate clearance from potential fasteners. Certainly this install might be approved by the local muni-inspectors.

**Jerry Peck** · 08-15-2021, 05:17 AM

Think of it as the NM cable being run on a block wall between furring strips ... how does that effect your thinking of it.

**Claude Lawrenson** · 08-15-2021, 04:06 PM

Originally Posted by Jerry Peck

Think of it as the NM cable being run on a block wall between furring strips ... how does that effect your thinking of it.

Thanks, do not often see it that way. I just looked it up and found this -https://www.jlconline.com/how-to/interiors/q-a-installing-wiring-between-ceiling-strapping_o

**Jerry Peck** · 08-15-2021, 05:39 PM

Correct: "where a cableor raceway-type wiring method is installed parallel to framing members ... the cable or raceway shall be installed and supported so that the nearest outside surface of the cable or raceway is not less than 1 1/4 inch (31.8mm) from the nearest edge of the framing member where nails or screws are likely to penetrate."

The floor truss and furring strips are "framing members"; however, the floor trusses "where nails or screws are likely to penetrate" for the nails or screws attaching the furring strips; it is the furring strips "where nails or screws are likely to peenetrate" for the nails or screws attaching the drywall. Thus it is the furring strips which lower the "nailing surface" away from the floor trusses bottom surface down to the furring strips bottom surface.

If drywall was to be considered a nailing surface for nails or screws other than those which attach the drywall, then furring strips on block walls and concrete walls would have to be larger than 2x2 to provide that 1-1/4" space plus the size of the cable (1/2" for cable + 1-1/4" = 1-3/4" ... face of 1/2" drywall + 3/4" gives 1-1/4" to 1/2" cable, so 1-1/4" + 1/2" = 1-3/4" ... a 2?2 is only 1-1/2").

I haven't seen any 2?3 furring, much less on edge to clear that 1-3/4" needed.

Drywall is not a nailing surface, one nails through drywall to the nailing surface behind the drywall.

Typing on my phone - did I type the math correctly?

**ROBERT YOUNG** · 08-15-2021, 06:05 PM

Originally Posted by Jerry Peck

Correct: "where a cableor raceway-type wiring method is installed parallel to framing members ... the cable or raceway shall be installed and supported so that the nearest outside surface of the cable or raceway is not less than 1 1/4 inch (31.8mm) from the nearest edge of the framing member where nails or screws are likely to penetrate."

The floor truss and furring strips are "framing members"; however, the floor trusses "where nails or screws are likely to penetrate" for the nails or screws attaching the furring strips; it is the furring strips "where nails or screws are likely to peenetrate" for the nails or screws attaching the drywall. Thus it is the furring strips which lower the "nailing surface" away from the floor trusses bottom surface down to the furring strips bottom surface.

If drywall was to be considered a nailing surface for nails or screws other than those which attach the drywall, then furring strips on block walls and concrete walls would have to be larger than 2x2 to provide that 1-1/4" space plus the size of the cable (1/2" for cable + 1-1/4" = 1-3/4" ... face of 1/2" drywall + 3/4" gives 1-1/4" to 1/2" cable, so 1-1/4" + 1/2" = 1-3/4" ... a 2?2 is only 1-1/2").

I haven't seen any 2?3 furring, much less on edge to clear that 1-3/4" needed.

Drywall is not a nailing surface, one nails through drywall to the nailing surface behind the drywall.

Typing on my phone - did I type the math correctly?

You did fine, Jerry.

As well electric cables carrying low voltage current can not come into contact with conductive plumbing or heating supply surfaces. I forget what the clearance rules are. I think .5" inch.