To answer you materiel question, you should check the spec.s on the box or ask a clerk if you can look at the installation instructions. Frequently this info is linked on the merchant's/maker's web site.
If your bathroom has an attic space over it, I'd suggest you box in a 'chimney' over the hole in the ceiling. Install the fan unit on top of this chute. The next time you need to replace or service the fan you will not have to do any construction, it's practically plug-n-play even with dis-similar products. If there are women in you house-hold the fan/impellor may be jammed with deposits of hair-spray and dust. Scrape it off and there's a good chance your problem will go away.
I've never heard of a bathroom fan that includes a heating unit. Usually they get mounted in the ceiling which is not the most efficient place for a heat source. Not being a ventilation expert it appears that I have a gap in my knowledge though.
