Joist Bay as Return

[klipper]

Hey,

I'm having some HVAC work done and we're rerouting some returns. My buddy wants to use the joist bay in our unfinished basement as the "duct" for part of the return.
The idea is to sheet metal the bottom of the joists, enclosing the bay, and with the subfloor and floor upstairs, it will be airtight.
I've never heard of this. Have any of you?
Is is safe? Functional? a good idea?
Please let me know.
Thanks

[fixit50]

Like this????????

http://www.tvmi.com/rfoil/H107.htm

[klipper]

Yes,

except with sheet metal and not rfoil.
This isn't such crazy idea then?

[dash]

Okay if it's truly air tight(all sides and the ends),in our area it's not allowed by code,as the wood is flamable.I know it's common in other parts of the country.


Oh,it also needs to be large enough to handle the airflow required,may need more than one.

[condenseddave]

Very common, just bear in mind that you can only do that with the return, and sealing it to the return ductwork is necessary.

There are other products available, such as thermopan, and the dubble-bubble that can be stapled up, but sheet metal panning is the best way to go.

[klipper]

The joist bay is 14" by 9 1/2"

"sealing it to the return ductwork is necessary."

You mean connecting it to the return so it functions, right?

Thanks for your help!

[condenseddave]

Yep. You want to attach the panning to the joists with roofing nails every 4-5". The panning should be sealed off from the area that it's in, and the ductwork should be connected to the panning. IOW, don't leave the panning open on one end and defeat the purpoose of the panning.....

[klipper]

Ok,

I get it.
We're cutting a hole in the floor and running a duct UP from that hole. That duct will have vents for returning air.
The joist bay under the hole is going to be sealed the length of the bay with sheet metal and attached to a duct on the other side of the house.
The duct it's attached to feeds the return on the furnace directly.

So, there's no opening's except for where the ducts are.
Thanks again, this site rocks!

[amickracing]

Just curious why you choose metal?

I know everyone (including me) preaches metal on this site (as opposed to flex). But sometimes the metal panning can "bong" when you walk across the floor, or as the house settles in the future.

Just throwin my 2 cents out there.

[klipper]

what are my choices?

[tinman]

Good stout metal 22 or 24 guage with a pitts on one end and a crossbreak. There will be no oilcanning.

[framehvac]

klipper Hey,

I'm having some HVAC work done and we're rerouting some returns. My buddy wants to use the joist bay in our unfinished basement as the "duct" for part of the return.
The idea is to sheet metal the bottom of the joists, enclosing the bay, and with the subfloor and floor upstairs, it will be airtight.
I've never heard of this. Have any of you?
Is is safe? Functional? a good idea?
Please let me know.
Thanks

Yes we do it all the time in wv we use duct board or metal to pan with check out your code first.

[amickracing]

Whoops, guess I should have posted what else you could use. I typically use a lot of thermo-pan (basically a cardboard type stuff). Also, it's true that a thicker metal (22 or 24 ga) probably won't "bong", but around here all I have ever seen is really thin, like around 30 ga.

[git-r-dun]

Same in Colorado. We do and use the same thing as you guys in WV