Are residential bathroom fans required to be controlled by a switch?

Not that I can think of ... assuming you can use the breaker for a disconnect.
It is not uncommon to see them on motion sensors.

Who, in a residence, could tollerate the HVAC drain that an unswitched fan would cause?

Just the noise, alone, would have the residents howling.

I have seen them on humidistat's in the hall and go off and on as required depending on the whole house level and not just the bathroom. Doesn't do anything for getting rid of the smell though.

In my 30 years of electrical experience, I have yet to see a bath fan NOT on a switch of some kind. Most of them go on with a light in the bathroom. I myself put them on timers, because my kids never remember to shut off lights and such.

Timers are better than switches because you want the fan to run after the shower / bath to allow all the humidity to exhaust out. If its on a light switch you only get ventilation while you are in there.

Somewhere I read or was told it should be running for 30 minutes after you get out to bring the humidity back to normal.

I agree with all of the responses. Switch is not required per code but common sense should prevail and it becomes a design issue.

I agree the switch is not required by the NEC. The exhaust fan also is not required by the NEC.

Some of the instructions with exhaust fans mention a wall switch in the installation instructions. So 110.3(B) may apply.

Also building codes and building energy codes may mandate an accessible wall controll for occupants.

New this year in Massachusetts, all venting has to be done by a HVAC installer and permits filed with inspections by the mechanical inspector.

This is fine by me...I never looked forward to drilling 4inch holes with a holesaw up on a 24ft extension ladder.

You find the fan requirement in the building code if your bathroom window is too small or doesn't open.

Typically that is 3 sq/ft with half opening.

Fan operation 'may' be addressed within the Energy Codes. I'll ask one of the Building guys today. I have not seen any without a switch, timer, or motion.

Most of the new comm are using motions (with override) in the restrooms.

Codes require ventilation in bathrooms. It can be either by fan or by window.

Just as there is no law requiring your car to have a speedometer, there is no requirement that there be any switch, anywhere, to turn the thing off.

There is certainly no requirement that the fan be on a switch separate from the light.

Code-required ventilation is a minimal requirement, and there are many situations where it is desired to have more. There are also physical reasons why it's desirable to have the (small) fan run longer, than have a (big) fan run for short periods. So, a healthy market has sprung up selling special timer switches for bath fans.