Two related questions:

  1. I have a problem section of heating vent that is 2.5" x 12". I thought I'd be able to find this size in Lowes or Home Depot, but nothing is even close (I see 3.5" x 10"). Note: This section handles the air into the furnace (from an upstairs register).

The question is: Where can I get 2.5" x 12" or does there exist some place I can order a converter?

  1. The reason for question #1 is a tricky one. I would have to provide some screenshots and way too much info, but I have reason to believe that removing this section altogether might be my best option for now. If I do this, I am concerned that I might be putting too much strain on the furnace.

Here is how it is configured. First, there is a very large air intake register (sorry, I don't know the terminology) upstairs that leads right into the furnace (about 4 feet of 3.5" x 12" ducts). The "problem" duct described above is from another intake register in another room. This doesn't go directly into the furnace. Rather, it comes right in the middle of that 4-foot section of the other air intake. I would imagine that this really doesn't provide that much more air to the furnace, but I could be wrong.

So, to summarize: 1. What to do about odd-sized ducts? 2. Can I just block off that additional air intake, or will my furnace explode? Thanks.

  • What is the problem with this section of duct, and why do you think you have to replace it?
    – Tester101
    Nov 3, 2011 at 18:21
  • Rather than connect the duct all the way up to the section of duct running to the in-vent upstairs, they simply nailed a huge sheet of aluminum to the joists, then attached the duct coming from the furnace to the aluminum sheet. So there is a "box" created by the ceiling, 2 joists, and a bunch of aluminum. It's way too complicated. I tried to draw it. I'm thinking I need to get some photos of this. Not only is this a mess, I think it may actually be pulling in some air from the crawl space under the attached porch on that side of the house. I am smelling a musty/moldy smell.
    – user980
    Nov 3, 2011 at 18:45
  • I want the air to be pulling from the upstairs - not from the basement (and elsewhere).
    – user980
    Nov 3, 2011 at 18:47
  • 2
    Creating a return vent in that way is very common. sealing any connections with metal tape, will prevent it from sucking air from unwanted places.
    – Tester101
    Nov 3, 2011 at 19:21
  • There may be some structural issues that are causing some air (potentially smelly air from under the porch) to be sucked in. I just want to go straight up to the stretch of duct going up to the wall.
    – user980
    Nov 3, 2011 at 19:43

1 Answer 1


The "odd size" is due to what was available at the time compared to what is available today. Your exact size may still be available, but not through regular retail outlets, they carry what's commonly demanded. A Heating & Cooling Contractor or their Supply Store may be able to get new replacements readily. Also, scour the Internet, as many suppliers are now offering their catalogs to the world.

If you don't find yourself adjusting the Registers regularly, then you may have a system that was precisely balanced & comfort is always fairly uniform. Changing the size of the Registers & therefore their duct box wouldn't cause a problem or difference, just don't change any actual duct sizes.

Finally, why not repaint them or totally refinish them, if they're in good working order? A trip to an Automotive Store will have the Spray Paint Remover & the new Spray Paint so you can fully restore them back to new in the color you want. Bent fins can be straightened, mangled screws can be replaced & detached operation knobs or handles that are still around (in their absence a longer screw or bolt can suffice) can be drilled & screwed for secure re-attachment.

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