Abt recommends 1 CFM per 100 BTUs. For example: a GE $1,000 gas range has five burners, totaling 47,000 BTUs. That implies you'll need a exhaust vent with a fan rated at 470 CFM. That's assuming, though, that you have all five burners on at the same time. In the bathroom, you might want to upgrade your fan if your stomach doesn't process burritos well.
What About Noise Levels? Common sense might imply that the more powerful the fan, the more noise it will make. However, that's not always the case. Better motors, blade size and shape, and other features make small contributions to the total amount of noise that a fan makes. What you should look for in a fan is the specified noise level, generally listed in sones. If you're escaping into the bathroom for some peace and quiet, the last thing you want is a loud fan buzzing in your ear. Other Factors It might sound simple, but make sure your fan fits! Many high powered bathroom fans are designed to slide into 2x6 or bigger ceiling joists, so if you don't have the space you might have to settle for a lower power model. Also consider when buying a range hood for your kitchen that the space above your range might not match exactly. If you have a 30" free standing range surrounded by cabinets, the upper cabinets on the sides might have end panels that eat into your 30" of available space. Also be careful to note where the fan exhausts (it's not always straight up, sometimes those stacks are cosmetic) and make sure you have a spot to run your exhaust outside. (Images: XPhantom/Shutterstock, Michael Higginson/Shutterstock)