WhisperSense DC Fan with Motion and Humidity Sensors Delay Timer and Pick-A-Flow Speed Selector 50, 80 or 110 CFM

No, it does not need a wall switch if the unit you bought doesn't have a light in it. I have two of these (model FV-0511VQC1) in my house. They are wired so the unit is always "hot" (power always on) and I have no wall switches. The fan will only come on when it senses motion and/or senses too much humidity. There are two dials in this this model that you can change-- One dial that controls how long the fan stays on once it stops sensing motion, and one dial that sets how much humidity the fans needs to sense before it goes on or off.

Yes. I ran mine out through the gable. About 15-20 feet of venting so I turned the cfm up to max (even though it's venting a small bathroom - it has a longer distance to vent). Works well.

The motion sensor is pretty sensitive because it has a 90 degree field of view and can sense motion up to 10 feet away. We have cats and they sometimes set off the motion detector of the unit. Luckily the unit is so quiet, it does not startle or wake us during the night. We also have the motion dial inside the unit set to only have the fan run for about a minute or two before it shuts off, so no biggie.

If you have the model FV-0511VQC1, it has two dials in there-- One dial to shut off the fan after a certain time after it doesn't sense motion anymore and one dial to shut off the fan once a certain level of humidity is no longer reached. Technically, if you don't have the unit with a light on it, you can wire the fan so it's "hot" (the power is always on) and not have a wall switch at all. The fan should turn itself off if either of the two criteria I mentioned above take place.

Determine the size of your bathroom with this formula: Length x Width x Height x 0.13 = Minimum CFM rating. From Home Depot URL:---> https://www.homedepot.com/c/ab/best-bathroom-fans-for-your-home/9ba683603be9fa5395fab90ab995103

These aren't made for dimmers or fan speed control switches. The fan in the unit is either running or off. There is a switch inside the unit that lets you choose one of three speeds for the air flow, but it must be switched manually and there is no other way to control that setting. Usually it's recommended you just choose a speed, see if it does the trick for you, and if not, try another speed.

sorry I can't give exact answer but mine is 15ft and no issues. The fan is a 6in exhaust and I reduced to 4in since that was existing.

As @buyquality indicated in his post---> "Not exactly. If you were to turn the switch on without entering the room the fan will NOT come on because no motion will be detected."::... Doesn't make sense to install with a switch as the motion detection serves the purpose to come on and stay on for the designated time after the last person leaves. To include a switch would only complicates the issue. If you use a switch might as well not go with the motion sensor and make the switch a countdown timer switch. The Panasonic Specifications sheet states---> UL listed for tub/shower enclosure when GFCI protected. I would wire the Panasonic fan to comply with whatever GFCI protection that is accessible and in place with your house, as in the bathroom protected GFCI receptacle and forgo the switch. If you want a switch then that would be placed as GFCI protected and would be put somewhere not so convenient as it would be left on. Anecdotally why would you want to explain over and over to your guest to leave the fan switch on when without the switch it is simple, walk in fan comes on when you're done leave.....

If it senses motion, the fan will stay on anywhere from .5 to 60 minutes depending on how you have the timer dial set in the unit itself. See pic below (sorry for the dust on it!)

I would recommend a separate switch so it can be controlled independently of the lights.