There is a 3'x3' opening in the ceiling of my second (top) floor. The opening leads into the unheated attic. I want to both seal and insulate this opening to keep out the cold in the winter. (I live in New York, were it can get cold.) I already have built a box around the fan in the attic using hard pink insulation, But it does not seal perfectly and is not all that well insulated.

How might I secure a 2"x3'x3' box to the underside of the opening (i.e., in my second floor hallway)? The box would contain 1.5" hard, pink insulation in this box and would have a 1/2" cover framed with 1"x2".

How might I attach this to the ceiling so that it will be a tight fit but easy to take off in the spring?


P.S. These related posts do not cover this question. How do I insulate a whole-house fan during the winter?

Here are photos of the vent opening and fan.
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UPDATE: I did something like the answer below. I built a square using 1x2's on top of a 1/4" 3' square plywood sheet, and filled it with rigid pink foam. I put soft foam tape on the edges of the 1x2's. In the ceiling I put the wood end of Wood to Metal Double Ended Screws. I attach the box to the ceiling with wing nuts. (See phooo.)


  • If that louver is steel I'd look at using magnetic tape.
    – isherwood
    Commented Nov 29, 2017 at 17:19
  • @isherwood I've used a sheet of plastic in the past. That ended drafts but provides zero insulation.
    – Yehuda_NYC
    Commented Nov 29, 2017 at 17:38
  • 2
    I'm not sure what you're saying to me. Build your foam panel and attach it with magnets.
    – isherwood
    Commented Nov 29, 2017 at 19:02
  • Magnets might be strong enough to support a foam panel. I was thinking of putting the foam in a wooden box, which would weigh too much. But your idea seems practical. Thx.
    – Yehuda_NYC
    Commented Nov 29, 2017 at 19:04
  • The reviews of magnetic tapes on amazon are lukewarm. Is there a style that has good holding power?
    – Yehuda_NYC
    Commented Nov 30, 2017 at 21:25

1 Answer 1


I know this is old but, might help someone?? It looks like there are twelve screws holding up the louvered flap register. I would build the box and use four of those holes (one on each side) to secure the insulated box. You'll need four longer screws to compensate for the added box. To make it air tight to the register line the top edges/border with foam tape. Another similar option is to cut a piece of whatever thickness plywood, paint it white and line the top with some of that rubber hardwood floor underlayment and screws it on the same way as above. Hope this helps someone.

  • 1
    That's actually a really good idea!
    – FreeMan
    Commented Aug 25, 2021 at 11:38
  • I did something like that. I updated the question.
    – Yehuda_NYC
    Commented Oct 26, 2021 at 1:10

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