I have what I think is a Broan 670 exhaust fan installed in my bathroom. I would like a fan/light combo instead. I am unable to easily access it from the attic so I am hoping to replace it from the bathroom itself.
My first preference is to keep the housing and replace the fan with a fan/light combo. My second option is to replace both the housing and the fan but maintain the same dimensions (7.25" by 7.5"). My third option will be to just completely replace the fan and expand the opening if needed.
I found a Delta Breez ITG80LED which seems to be the same width and length.
Question: How do I know if it's possible to reuse my existing housing with this fan/light? Or is that only possible with a replacement Broan part (which I can't seem to find with a light) and should I plan on replacing the entire housing?
Photos of existing fan, for reference:
Bear in mind there's a bit of margin for error in this trick but as you can see, the diameter of the cutout would be roughly 13 1/2". You may have to ream out your drywall a bit but that's better than having a hole that's too big. And remember your grill is 15" so you'll have aprx. 3/4" of fudge room all around. In all likelihood the drywall cutout won't be an issue, but you'll probably have to modify the blocking to accept the new unit, which (as long as your framing is as it should be) won't be too much hassle.
Best Answer
It is highly doubtful that it would be possible to simply place the guts of a new fan unit into the housing of an old fan, especially when it is a different manufacturer. In addition the fact that the new one has lighting in it means that there will be different wiring provisions inside the new housing for two circuits and your old housing only accommodated a single circuit.
The differing models are also highly likely to have differing size and type of fan blade assembly and air guides as well. Attempting to deconstruct both the old and new units to be able to swap parts just to save an old external housing might be possible but it is not something you are going to do reaching up into the ceiling. Instead you would have to have both units out on a workbench to perform the surgery. Such work would likely include breaking spot welds and needing to drill holes and use sheet metal screws to reassemble. But hey if you have it out on a workbench why not just mount the new one in the ceiling.
It has been my experience that you can replace the fan from below (I've done it on flat roofed houses where there was no attic) but you should plan from the outset to remove the ceiling drywall back to the center of the next ceiling joist and make the cutout be large enough that you can work through it. You will need access to:
You did say you had an attic...even though access may be difficult it may still be less work overall to replace your fan from above even if the clearance to rafters is only a foot or so.