Designing Kitchens and Bathrooms - bathroom exhaust fan replacement

I would like to replace our bathroom exhaust fans with quieter ones that are Energy Star efficient. The fans are so old that I am having trouble removing the screws from the vent cover! How will I know if the fans are properly vented to the outside of the house soffets and how do I know what size (CFM) and strength to get for the room? I saw something about 1.5 x sq feet of room = cfm rating...is that right? Also, I want to make sure that it is super quiet. Any advice on that front as well please?

The formula for sizing the fan is generally correct. How far you have to run ducts to get to the outside is a major factor in sizing. Long runs and elbows dictate more air flow. If there is an attic space over the bathroom, you can check for proper venting to the outside. I don't recommend using corrigated flex vent unless space is very tight. Rigid metal duct offers the least resistence to air flow.

Panasonic and Broan make quiet fans. But it is likely you will have to alter the cutout for the fan, usually needs to be larger.

thanks much. If I wanted to hire someone to do this for me, is this something that any handyman could do or would I need to hire an electrician or otherwise?

Local codes can be an issue, but from a reality standpoint, it does not take an electrician to replace an existing fan. He likely would not do drywall repairs should you install a physically larger fan, anyhow. So one person should be able to do the job. One persons definition of a handyman may be different for others, but probably yes.

I had a loud exhaust fan. After careful dismantling (e.g. turn off breaker, just in case), I noticed that the actual cage fan was a bit wobbly. The big box stores carry "upgrades" for recent fan models. These upgrades contain a different motor that is supposed to be more efficient and quiet. I couldn't find one for my model, which I could still read and why this may not apply to you, but found a parts vendor off the manufacturer's web site. $60 later, I had a new cage, bearing and I-forget-what-else assembly that I screwed in place and fixed my noise issue. The big advantage for me was that by not ripping the old fan out, I didn't risk breaking the ceiling sheet rock, which would have required patching and painting to repair, thereby turning a 1 hour job into several hours.