I have a Broan 659 heater/fan/light for my bathroom that is ready to install. It was about the only combo unit I could find for this size hole, which is why I bought it. You can see a copy of the instillation manual here

I got out the directions and discovered that I'm supposed to mount it using adjustable mounting brackets to fasten the unit to the joists.

The space over the bathroom is unfinished attic with blown in insulation accessed through small panel in a closet ceiling. I really don't want to go up there! Is there any other way I can safely install this combo unit? And is it safe to cover this unit with insulation after it's installed?

Fingers crossed there is another way to do this...

They can mount up thru the ceiling hole, but is usually works better if mounted from above. Electric wiring and ducting has to be done from above, so why not mounting???

As for the hole, no need to find one to fit a small hole, simply enlarge the hole. Going the other way requires some drywall patching, but can be done.

The wiring and ducting is already in place.. (I'm replacing an old, broken unit.) I just hate hate hate going into the attic!

Just to verify your wiring that's in place. This unit requires a dedicated 20 amp circuit. It also requires a 12/3 cable and a separate 12/2 cable be run from your wall switches to the unit. You'll also need a 3 function switch if you only have a single gang wall box installed.

Dora brings up good points. Assuming you have dealt with those issues, you can indeed install a replacement fan without going into the attic. I've done it a number of times and it has to be done when there is no attic above the bathroom as is the case is two story homes for example.

Since I can't use the the mounting rails on the new fan or the typical flanges that attach to the joist, I locate the fan in the hole and drill through the metal frame (after the fan plate has been removed) near each corner. Get the holes as high as possible so you don't interfere with the fan plate. Then, I drive screws through the holes and into the joist. I recommend using a small washer on the head of the screw to distribute the load.

I've even put small isolation pads between the joist and fan box to reduce noise, but, that seems optional in most cases.

Good luck, Bob.

Thank you so much for the guidance! Yes, the wiring is already done and up to the task. --I had some electricians in last year to put in a sub panel (beyond my skills) and they ran a dedicated 20 amp circuit from that panel when they were here.

Not having to go to the attic is a relief, taking his from epic scale dreaded task to something I can do in an afternoon.