Home HVAC Ducting Question

[DavidI]

While renovating an upstairs bathroom, I was able to access a drywalled off chute that comes from the ground level garage to the second story attic. This space is where the main ducting trunk comes from the top of the furnace blower coils, blowing upward into the attic where the ducting branches throughout the house for the central heater/air conditioner system. I have lived in my home for nearly 30 years and have always been unsatisfied with the air volume put out be the central air/heater. Then I discovered this:

The 14" vertical flex ducting is severed approximately two feet above the second story floor. This accounts for the lack of air volume for my system! My plan is to purchase a 14" metal connector, use the long zip ties made for connecting flexible ductwork to metal connections, then use the silver foil duct tape to ensure a tight connection.

All of that makes sense to me. My question is this: After repairing the ductwork, the new vertical section will have the extra weight of the 14" metal connector and it will put additional stress on the zip ties and foil tape. I fear that this could fail over time and may need some support.

Space in this chute is small, but I was able to precariously wiggle a step stool into the area. In the rafter above the ductwork, I drilled a hole and screwed in an eye hook. From this, I suspended three nylon straps allowing them to dangle directly above the ductwork. My intention is to make the secure connection between the ducting, then use sheet metal screws to tap the nylon straps into three sides of the metal connector to support the weight. I will also foil tape over the screws and I think mastic is way overkill in this case.

I don't want to make the connection repair, re-drywall the area limiting my access, then have it disconnect in the future.

Because the area is so small and dark, taking a photo is very difficult. Hopefully, I described the plan in sufficient detail.

Any suggestions or ideas for supporting the weight?

[masraum]

I'm not a duct or HVAC guy.

But I think your plan (now that I've read your whole post) sounds good.

Is there any framing in the chute?

Could you wrap something like plumber's strap around the metal portion (with a sheetmetal screw or two through the strap and into the duct connector) and then screw the plumber's strap to the framing of the chute?

[javadog]

Most of the time they use metal strapping and sheet metal screws. It's generally not very sophisticated. Probably anything would work. In the commercial world, ducting is usually rectangular section metal, supported by unistrut. Overkill, in this instance.

You DO want to support the ductwork. But, don't overthink it.

[javadog]

https://basc.pnnl.gov/videos/support-intervals-flex-ducts-1

[Zeke]

@javadog, that video is excellent. But few installers do that much work. No more than 1/2" sag in 4' is a tough goal for flex ducting.

@DavidI, I think you did everything you could. The extra weight is likely not as big a factor as you think. Your plan sounds great. Just want to make sure I understood that you added support below the repair.

[DavidI]

Originally Posted by masraum

I'm not a duct or HVAC guy.

But I think your plan (now that I've read your whole post) sounds good.

Is there any framing in the chute?

Could you wrap something like plumber's strap around the metal portion (with a sheetmetal screw or two through the strap and into the duct connector) and then screw the plumber's strap to the framing of the chute?

This is what I am thinking. I intend to use nylon straps attached to an eye bolt screwed into a rafter above the flex ducting.

Thank you!

[DavidI]

Originally Posted by javadog

https://basc.pnnl.gov/videos/support-intervals-flex-ducts-1

Much appreciated Java!

[DavidI]

Originally Posted by Zeke

@javadog, that video is excellent. But few installers do that much work. No more than 1/2" sag in 4' is a tough goal for flex ducting.

@DavidI, I think you did everything you could. The extra weight is likely not as big a factor as you think. Your plan sounds great. Just want to make sure I understood that you added support below the repair.

The nylon straps will be attached to the rafter above the flex duct on one end and the other will be sheetmetal screwed into the metal connector. There will be 3 separate nylon straps attached to the metal connector to support the weight. I don't think it'll be too heavy, but over time I don't want the ducting to collapse due to its own weight.

Thanks Milt!

[Zeke]

You were worried about the tape separating, I just wondered if the duct below the splice is hanging by the tape to the metal collar. I think if you tie-wrap over the tape, or on the duct below the tape while still on the collar, it will last just fine.

All I'm pointing out is that IDT tape is meant to hold anything that is trying to pull against the splice, You need that mechanical attachment. I think I understand that's what you've done, but not sure.

[look 171]

Don't over think it. screw the metal connector you installed to a couple of cleats that are nailed or screwed into the studs near by. for the lower section, strap the lower flex parts to the same thing to keep gravity from pulling it apart. Alum tape on top of straps if you think its necessary to make it more secure. It wil lstay for a long, long time.

[look 171]

Originally Posted by Zeke

You were worried about the tape separating, I just wondered if the duct below the splice is hanging by the tape to the metal collar. I think if you tie-wrap over the tape, or on the duct below the tape while still on the collar, it will last just fine.

All I'm pointing out is that IDT tape is meant to hold anything that is trying to pull against the splice, You need that mechanical attachment. I think I understand that's what you've done, but not sure.

Gravity yanked the joint apart over time inside the wall. I agree, mechanical fastener is the key.

[cabmandone]

I'd have done exactly what look171 suggests in #10 either from the inside or through the studs into the metal pipe with longer screws.

[DavidI]

Originally Posted by look 171

Don't over think it. screw the metal connector you installed to a couple of cleats that are nailed or screwed into the studs near by. for the lower section, strap the lower flex parts to the same thing to keep gravity from pulling it apart. Alum tape on top of straps if you think its necessary to make it more secure. It wil lstay for a long, long time.

Thank you Look!

[DavidI]

Originally Posted by Zeke

You were worried about the tape separating, I just wondered if the duct below the splice is hanging by the tape to the metal collar. I think if you tie-wrap over the tape, or on the duct below the tape while still on the collar, it will last just fine.

All I'm pointing out is that IDT tape is meant to hold anything that is trying to pull against the splice, You need that mechanical attachment. I think I understand that's what you've done, but not sure.

Thanks Milt. I first intended to use the long zip ties as a band, but yesterday I ordered some stainless steel bands to connect the metal coupler to each open end of the flex pipe. On top of the bands, I will use silver foil duct tape. The coupler will be held vertical by the suspended nylon bands to support the weight so it is not placed on the tape and bands.

I appreciate it, David

[cabmandone]

I'd use something like Gorilla duct tape rather than the foil tape. I've seen foil tape let loose due to condensation. When I did install, I'd tape the inner liner to the metal sleeve, run metal screws through the tape pinching the wire that is in the inner liner then pull the insulation and outer plastic over the inner and tape that to the sleeve. Do the same with the other end being spliced, but tape the outer plastic to the other piece I just taped down to the inner sleeve (If that all makes sense)

[Zeke]

Originally Posted by cabmandone

I'd use something like Gorilla duct tape rather than the foil tape. I've seen foil tape let loose due to condensation. When I did install, I'd tape the inner liner to the metal sleeve, run metal screws through the tape pinching the wire that is in the inner liner then pull the insulation and outer plastic over the inner and tape that to the sleeve. Do the same with the other end being spliced, but tape the outer plastic to the other piece I just taped down to the inner sleeve (If that all makes sense)

Screws clamping the wire, that a great idea.

[DavidI]

Originally Posted by cabmandone

I'd use something like Gorilla duct tape rather than the foil tape. I've seen foil tape let loose due to condensation. When I did install, I'd tape the inner liner to the metal sleeve, run metal screws through the tape pinching the wire that is in the inner liner then pull the insulation and outer plastic over the inner and tape that to the sleeve. Do the same with the other end being spliced, but tape the outer plastic to the other piece I just taped down to the inner sleeve (If that all makes sense)

Much appreciated Cab! That is my plan, David

[DavidI]

Update - I initially purchased a metal duct connector from the local AC Pro store. It has a 14" diameter, is 15 1/2" long, and weighs a little over 4 pounds. The size and weight of the connector is what concerned me regarding the support.

I ordered another connector from Home Depot. It has a 14" diameter, is 5 1/2" long and weighs a little over a pound. This one seems more reasonable for my application and I'll return the larger heavier one. The larger one seems to be more for commercial grade than residential. Refer to the included photo for a comparison.

Thanks for all the advice and suggestions, David

[javadog]

The one on the right can be adjusted from straight, to a 90 degree elbow. That’s why it’s heavier.

Totally different thing.

[look 171]

One on left is fine. Just make sure you have a way to secure it from gravity and secure the lower flex ducts. Gravity is not your friend here. Use mechanical fastener. For flex, use straps and tape.