Fitting the Fan Into a Wrong-Size Hole

When the wall fan in our downstairs bathroom quit, I figured we could easily replace it, so I took measurements and bought one that had the same dimensions as the old fan. It did, however, have a different arrangement for the fan and exhaust port. But I thought it would easily fit the space occupied by the old unit.

It didn't take long to remove the old fan, because the back was easy to access from an unfinished section of the basement. It looked like the job would take only a few minutes. Unfortunately, the fan body would not go through the old cutout from the bathroom side due to the arrangement of the fan chamber and exhaust port. The fan manufacturer got a strongly worded letter afterward about poor engineering of a product billed as a drop-in replacement.

I could get at the hole in the wall from the basement side, but mounting flanges along the front edge of the fan prevented me from pushing the fan through from the basement side. The fan was just too big. I had no room to cut the drywall to make a bigger hole. After a while, it dawned on me if I couldn't make the hole bigger, I could make the fan smaller.

Here's how I did it. I made a cut with a hacksaw at about the middle of each flange, which let me push in, or deform, the fan body so the front looked like a four-pointed star. Thus, the outside dimensions of the flange became smaller, and the front of the fan easily passed through the opening. Then I "expanded" the front of the fan box back into a square and secured it in place with several screws into the wood around the original hole.

This entry was submitted by Jon Titus and edited by Rob Spiegel.

Jon Titus has designed electronic equipment, and is a contributing technical editor for Design News. He worked as chief editor of EDN and Test & Measurement World magazines for many years. He now lives in the Salt Lake Valley in Utah.

Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.

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