HVAC ductwork question...

Richard · Feb 12, 2022

We added on a room. Had the HVAC people extend system to room. (this was 8 years ago) Finally getting around to finishing the room (drywall, closet doors, tile flooring...)

When they brought the duct to the room, it came to the ceiling. The ceiling joists are (didn't measure, let's call them 16" OC) The SIX inch ductwork came into room, they had a formed metal 'elbow' that then housed a rectangular vent. The type that I would say is a floor vent with the tab to change the airflow.

This vent was too small to be held between the joists so they installed (rough measurements since it's in my car) they installed a piece of sheet metal, LOOKS like it's factory made. Let's call it 25" by 6-7 inches and in it, is a rectangular cutout that magically, the register then fits into.

Wife doesn't like any of that. She wants a ROUND vent up there, not a rectangular that's already installed. Sigh.

Disassembled the register, took sheet metal off. Got a 90 degree elbow, damper and am ready to put things back. On putting back, I see that having a cross member brace to hole the ducting will be VERY beneficial.... I did NOT see this "joist hanger" type item when I was at the big box store.

I've taken to searching the internet. So far, I don't know what to call it so not sure how to search. I've not found anything like it yet. What I've seen are wire-ties that you mount to ceiling so you can suspend ("hang") the duct and that is not what I need.

I'm about to just use some perforated straps and mummify it up there before the drywall goes up. Thought I'd look again so am here asking.

It would be a piece of sheet metal long enough to span two joists. It would have a 6" cutout for the elbow to mount to. Drywall covers all this.

Any clue if it exists, what it's called and where I can get one? (probably have to ship it)
Monday, I'm going to call the HVAC people back and see if they have that version on hand and simply buy from them if so. So finding it online is my plan "B" in case they don't have them (might explain why they put the rectangular version in it....they did rest of house and put the rounds everywhere else but the ducting elsewhere allowed them to screw it to the joist. I tried to pull this to the side and it's fighting back (though I could perhaps use a longer screw, just thought of that) But this is where the perforated strapping is also coming to my mind.

Appreciate any thoughts.

Sigarms · Feb 12, 2022

Richard said:
We added on a room. Had the HVAC people extend system to room. (this was 8 years ago) Finally getting around to finishing the room (drywall, closet doors, tile flooring...)

When they brought the duct to the room, it came to the ceiling. The ceiling joists are (didn't measure, let's call them 16" OC) The SIX inch ductwork came into room, they had a formed metal 'elbow' that then housed a rectangular vent. The type that I would say is a floor vent with the tab to change the airflow.

This vent was too small to be held between the joists so they installed (rough measurements since it's in my car) they installed a piece of sheet metal, LOOKS like it's factory made. Let's call it 25" by 6-7 inches and in it, is a rectangular cutout that magically, the register then fits into.

Wife doesn't like any of that. She wants a ROUND vent up there, not a rectangular that's already installed. Sigh.

Disassembled the register, took sheet metal off. Got a 90 degree elbow, damper and am ready to put things back. On putting back, I see that having a cross member brace to hole the ducting will be VERY beneficial.... I did NOT see this "joist hanger" type item when I was at the big box store.

I've taken to searching the internet. So far, I don't know what to call it so not sure how to search. I've not found anything like it yet. What I've seen are wire-ties that you mount to ceiling so you can suspend ("hang") the duct and that is not what I need.

I'm about to just use some perforated straps and mummify it up there before the drywall goes up. Thought I'd look again so am here asking.

It would be a piece of sheet metal long enough to span two joists. It would have a 6" cutout for the elbow to mount to. Drywall covers all this.

Any clue if it exists, what it's called and where I can get one? (probably have to ship it)
Monday, I'm going to call the HVAC people back and see if they have that version on hand and simply buy from them if so. So finding it online is my plan "B" in case they don't have them (might explain why they put the rectangular version in it....they did rest of house and put the rounds everywhere else but the ducting elsewhere allowed them to screw it to the joist. I tried to pull this to the side and it's fighting back (though I could perhaps use a longer screw, just thought of that) But this is where the perforated strapping is also coming to my mind.

Appreciate any thoughts.

Apologies, not certain what your referring to per your description, but a picture is worth a thousand words. Worst case, I can only guess your looking for a insulated diffuser box (which is generally custom made) that the supply will tap into and then run a short length of round duct to the outlet?

Is the 6" (off the main duct) hard pipe with insulated wrap or is it flexible duct and what it the total length to near the outlet?

End of day, running 6" off of main trunk for a new space is pretty much only a bandaid and hoping for the best IMO with a lot of variables at play per the existing duct system.

Is the existing system zoned?

The bigger question that ensures it's done "right" is was a manual J & D done on the existing home with an added design for the new structure that was built and how the existing HVAC system will handle the additional load of the new conditioned area that the original system wasn't designed for?

As far as a round ceiling diffuser...

Richard · Feb 12, 2022

I get it.... apologies. I'm actually working on my camera right now as I type.

What I'm looking for interfaces BETWEEN what you show, and the actual 6" elbow. right now, I have the flexible ductwork up there, flopping around (dangling down) so it needs to be anchored in place. It's between the joists. They had this metal thing, mounted to the joists and this is what held the ductwork and vent.

I'll be getting a picture in a minute.

Richard · Feb 12, 2022

I'm laughing. If you knew the gymnastics I had to go through to get this... heh.

Anyway, the flex pipe comes out the wall at the ceiling. I need to turn it 90 degrees. They had the boot thingy. I bought a 90 degree fitting that you can rotate to change the angles. So I've got the vent coming out of the wall, into the 90 degree fitting...but need something to hold it in space. They had this item sitting on the right.

It was mounted to the joists, the pictured duct was mounted to the holder and all is well.

I've converted to a ROUND vent so would like to find the item on the right, except with a round cutout verses rectangular.

Given I've got a picture, this is more than 1,000 words!

Birdhunter1 · Feb 12, 2022

I used to be an HVAC guy and we made alot of stuff like you are talking about that would hold a boot in place in a ceiling but there is nothing wrong with framing what you want in wood and nailing through the boot or using sheetmetal screws through the metal into the wood. Of course that work was long before cell phone cameras so I have no photos of the work I used to do. We rarely ran flex duct as the boss hated it but we often used basset hangers to suspend flex duct or hard metal pipe in joist spaces, but again there is nothing wrong with attaching a board across the span to hold it up. Unless something drastic happens it will never move while just laying in there once your sheetrock is up, you don't want to neccessarily use the sheetrock itself to hold your boot and register but it doesn't take much to hold a 6" register.

Richard · Feb 12, 2022

There is going to be an adjustable damper mounted AFTER these two are attached. Then the diffuser will go in after the drywall goes up (obviously)

Birdhunter1 · Feb 12, 2022

I was typing my previous response when you posted the photo. From what you are describing is you have a 90* elbow and you are wanting to know how to frame it in place so you can drywall around it. A 2x4 frames across on two sides of your elbow and a screw through it (from inside preferably) will hold it in place for life and allow what you are wanting to do. completely boxing it in wouldn't be bad either just mount it in a manner that doesn't oval your pipe where your register will go in.
A picture of where it is going will help, but mounting this in a professional looking manner isn't rocket science. As long as it is held is the key, it isn't going to get major forces applied to it to make it move once it is in there.

Richard · Feb 12, 2022

One thing I think I discovered this morning (keep in mind this room was an addition, they left the 10" joists because they either screwed us or since it's a small room.... but this is a different conversation)

Anyway, I've noticed that this ductwork is going to be a snug fit up there. Since it's a "plastic" (no idea what it's made of) liner that attaches to the duct, then it has insulation around it.....it's flexible and looks like it WILL fit.

The issue is going to be by the time I turn the 90 degrees to bring it below the face of the joists... it's going to be extended maybe 1 1/2"-2" because of the depth of the space (or lack of). So I can see that this is maybe why they used the pictured version, it takes up less depth.

Ultimately, all I need to do is bring it into room (ducting already there) attach it to a plenum or something where I can have the air coming in, turn 90 degrees so I can bring it through the drywall and I've got a 10" space to do this.

Birdhunter1 · Feb 12, 2022

The Basset hangers I mentioned earlier. The last time I used one or bought any it was from our supplier and it was probably a box of 1000, I'm sure there is something at Lowe's or Home Depot very similar.

https://www.acandb.com/hvac/hangers/a-1-galv-bracket-adj-12-19?gclid=Cj0KCQiA0p2QBhDvARIsAACSOOPneutasi-hOhzapXp8bxRITRuDVEdFAXyrO7NfvZx2VT0eofoajlwaAqt3EALw_wcB

Richard · Feb 12, 2022

Just took some pictures of the location. Take me a minute to get them hammered into shape for posting here. Walking back and having read what you wrote....it dawned on me, I could also maybe just block it off with wood. Bring duct into the wooden box, then cut a hole in the bottom for the output side.

Never thought of that.