I am going to be attaching a piece of wood to a thin window sash in order to attach a rather heavy window fan to it. I will be using a wood screw to attach the fan housing to the strip of wood (I cannot attach the fan housing to the window sash directly since the wood needs to be wider - and I want to avoid doing damage to the sash, if possible; I hope I'm using term sash correctly: the side strips of wood that the window frame is attached to).

The problem that I see is that the space between the screw head and the fan is essentially nothing (maybe a 1/2") - not enough room to use a standard screwdriver to access it. Since I may want to take the fan out annually, I need a screw that can be accessed fairly easily.

How wide should the strip of wood be to accommodate this screw that you suggest, and the weight and vibration of the fan? Last question, what type of nail/screw or whatever should I use to attach the strip of wood to the molding?

I want to install this fan in the window - so the window can be closed (the typical installation for this type of whole house fan). I must leave a 1/4" gap between the vinyl window and any screws that go into the frame (in order to avoid damaging the integrity/warranty of the window and allowing space for the lip of the window for opening/closing).

I thought attaching a piece of wood to the sash (inner) would be better than trying to reverse the shields and try to attach it to the outside molding because the storm shields would leave a gap; this loses the efficiency of a whole house fan if there is a gap.

Because of the weight of the fan (and its top heaviness from the motor) I plan to put at least an 8" board on the window ledge to help it from falling and putting too much stress on the rest of the attachment points - with the vibrations and all. And legs, if needed. I've seen others make a box but I'm not sure how to do that.

Thanks, much!





  • 4
    If you have only 1/2" clearance, then your maximum screw length is 1/2" even if you could drive it with a wrench, like a carriage bolt. Would this even get through your wood & hold a fan? I think we need pictures of this location & proposed components to see if a better solution can be found.
    – Tetsujin
    May 22, 2022 at 18:48
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    Pictures and/or drawing would be helpful. This may also be a situation where you're better to concentrate on "how do I do the actual thing I am are trying to do" rather than "how do I do the difficult way I have thought of to do it" Sash is generally a movable part of the window, though "sash strip" may be the part of window frame you are thinking of - disambiguated by an annotaed picture - I'm ok with screws here, not here" or the like. Edit to add those.
    – Ecnerwal
    May 22, 2022 at 18:54
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    These are all good points. I think I need to go back to 'the drawing board'. I hadn't thought about my size restrictions. Lol! I'll add pics once I re-evaluate your thoughts to consider - if it is even possible. Thanks!!! May 22, 2022 at 19:01
  • 3
    If you can give us enough in pictures or drawings to see "what you have and what you don't want holes in (and where holes are OK)" we might well be able to come up with a way to do it.
    – Ecnerwal
    May 22, 2022 at 19:05
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    Thanks, Ecnerwal - and all the others. I'll draw up some details/ photos for you pros tomorrow and see what you think. The concept seems simple (just a couple of boards) but execution is another matter... clearly. Lol! May 22, 2022 at 19:10

1 Answer 1


The extended ledge for the fan to sit on seems reasonable. You should attach thin pieces at the front and back of the fan to prevent the fan from slipping in or out.

Precisely cut styrofoam (closed cell, not open cell) that fits into the channel in the jamb that the sash (sash=the unit that moves) runs in that also wedges the fan sideways. (Aim for 1/16" tight to ensure a good friction fit.)


The last bit is a length of wood across the top of the fan that fits precisely into the sash channel. It should be about double the width of the sash so that it sticks out in front and offers a place for a couple of screws that anchor the top of the fan. The bottom sash will sit on top of this board and hopefully seal well. If it doesn't, find something to fill the gap. (Sill gasket, backer rod, ...)

board on top

Happy to clarify if needed.

(Quick edit to say that this setup assumes the lower sash isn't going to get closed when the fan is in place... you might have to adjust the styrofoam a little and make the top board a very tight friction fit for this to work.)

  • Interesting, Aloysius! So the whole unit is held in place by the board on the top? That would solve the top heavy issue! (definitely will put a ledge on the bottom. Only thing is I will want the lower sash to open and close - during inclement weather, since I will be keeping the fan in place all season long. I will need to give a gap of about 1/4" from the window itself. Interesting. Thanks, much!! May 30, 2022 at 0:16
  • If you didn't mind a couple of screws into the jamb extensions (to the interior of the sash), you could put a couple of L brackets on the board across the top to keep it in place. May 30, 2022 at 14:09
  • Another great suggestion, Aloysius!! Jun 1, 2022 at 1:21

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