This is a stupid question, but I can’t find the obvious answer anywhere:
How do you install a ceiling diffuser box for AC?
Does it sit on the DW or should the edge be level with the bottom of the DW? Latter makes more sense for caulking, but the flange will get in the way.
What is the purpose of the flange on these things?
All I’ve got to go on is how my CAC retrofit was done in my house. The boxes sit on the DW, metal strips are wrapped around the edge of the DW and screwed into the sides of the boxes, and the vent cover then screws into those metal strips. The flanges are just screwed into the sides of the box.
At a guess, I’d imagine the vent cover is screwed into the flange, but I don’t see how that can be done unless someone is holding down the flange from above.
When I ask at the local HVAC store, I get blank stares. Looking for those metal strips on the internet.
Replies
I don't like to use a box like you show for supply registers, but rather what is commonly called a "boot". Sometimes called a "basement boot". They come in straight and 90 degree versions. The tabs or flanges on the boxes and boots are to attached to the structure. In a floor, a hole would be cut just over the side of the box and the box dropped through the subfloor, then flooring is installed over the tabs. In a ceiling, the boot goes in before the drywall, usually between joists and if the in trusses on 24" centers, extra pieces of 2x4 are added for rigid connection. On 16" centers, the tabs for a 10x6, 12x6 or 14x6 register will fall across the structure with no spacers required.
See http://www.standexadp.com/catstyle.php?prodcode=FG08&groupname=Diffuser%20Boxes #55
Edited 5/31/2006 11:51 am by Tim
So on a ceiling box, that flange is supposed to screw into ceiling joists? I can see the rail in the boot you linked to going both sides of a joist bay, not so with the diffuser box (#1000 in the same catalog). I've got a 6x6x5 box, I've elected to screw into the side of a joist, flange is doing nothing but getting in the way. I'll see if I can get one of those boots (#P5F in the Standex catalog) and make something of it.Thanks for your help.