extending vents in basement ceiling?


Old 11-30-02, 01:11 PM
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extending vents in basement ceiling?

im installing a drop ceiling in my basement,i have existing duct work there now that is even with the bottom of the joistes. what is the correct way to extend them down to the new height of my drop ceiling. it will a 3in. drop minus the thickness of the panels.they have 90 deg. boot on them now with a register attached.
Old 11-30-02, 10:24 PM
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I would suggest posting this question in the Repair forum under Heating and Cooling. We have some experienced HVAC moderators there that can really answer this with clarity.

From my experience, the boot that has metal lips attaches to your joists (16" o.c.). With a suspended ceiling, you may only have to acquire longer screws to reach the metal once you install your ceiling diffuser. In essence, the boot or extension should just be above your ceiling tile. Again this will vary depending on the type of difuser you are wanting, square, round or rectangluar.

They do sell a Suspended Ceiling Duct Kit if you interested at Home Depot.

Hope this helps!
Old 12-01-02, 07:15 AM
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The duct is usually supported by a metal strip fastened to the joist on either side. The boot itself is likely screwed to the joist. Remove the screw holding the boot. If the metal strap has enough slack simply bend it down to allow the duct to come closer to the required height. If not, remove one end of the strap from the joist, reduce the space between the joists to create slack. Take two small wood blocks, 1 1/2 x 1 1/2 x 4 and screw these to either side of the boot. Cut out your ceiling tile, set in place then screw the register to the blocking on the boot.
Old 12-01-02, 02:26 PM
Lew Falconer
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Good evening Mudcat. I've installed many suspended ceilings with exactly the same heating setup as you have. Unscrew the boot from the joist. Remove the metal strap altogether. The ducts will drop down far enough to rest on the ceiling tile. Just screw the register through the tile into the ears of the boot and let the ceiling support the duct. Works every time.
Have a good day and let us know how your project works out.

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