Pansonic Vent fan

Hi ,,I have an master bathroom that has no vent in it,the vent is in the water closet . I was in the water closet and notice water streaks on the paint which is the wall that seperate the water closet from the biugger master bath.
I am thinking of putting in a new 150 pansonic vent fan but this fan has an 6 inch duct on it.
My question is would a vent fan this size be an overkill ? And would venting to the soffit be a good ideal or bad?
Also would reducing the vent size to the vent pipe coming out of the water closet which is smaller be a bad ideal or not?
the master bath area is 13x12 water closet is 6x3 with 9 foot ceilings.
I have to replace the water closet vent also. thanks to all George

With the volume you have, and 150cfm fan, you'll get about 6 air exchanges per hour, which isn't too bad. Some of the Panasonic fans will work with either 4 or 6" ducts, but the distance you can vent it will be shorter with the 4" pipe - you need to read the specs very carefully. Some of them also allow you to customize the output (i.e, slow it down) should you need or want to for the best operation.

Panasonic does may a through-the-wall fan (don't remember the size) that I'd prefer over going out a soffit. FWIW, I put a Panasonic fan in my mother's house this spring and the outlet was actually stepped so that you could put either 4" or 6" ductwork on it...but, the outlet of the fan was actually 4". By expanding immediately to 6", the overall restriction isn't a big deal. I ended up using 6" since with the elbows I needed along with the length, that was what was called for.

Thanks Jim,,the old fan in the water closet has an 4 inch vent pipe. My question can I run the new vent pipe from the master bath area and tie it into the vent from the water closet? Also would the fan in the water closet draw air from the master bath since there is a door ? thanks george

The combined output of the two fans would likely exceed the capacity of the duct, so no, I do not think it would work. The air will go underneath the door, if required, to provide the flow to the fan - yes, it will come from outside of that room where the water closet is. Same thing overall, when you push air out of the room, some must come into it somehow - and, it might come through the duct to the other fan, should you connect them together. Or, it could be trying to blow the air out the other fan, defeating the purpose. It will go wherever the path of least resistance takes it.

There are some engineered, multi-inlet ventilation systems - Fantec is known for this and makes some nice products. They usually use a remote fan, which also means it is very quiet. FWIW, the Panasonic unit I put in is virtually inaudible unless you get right up next to it, at least with my decent, but aging hearing. I also put in a humidity sensing switch, but they also make some of the fans with this built-in. If the humidity (actually condensation) gets to the switch, it will turn itself on automatically. If you manually turn it on, it will automatically turn itself off after 30-minutes. Slick, especially when you have people taking a shower and they either forget or are too lazy to turn it on when needed. And, since you dont' have to worry about forgetting, and leaving it on forever, it will end up running long enough to dry out the room reasonably well rather than flipping it off when you leave before things have dried out.

I am going put in an 209 CFM by panasonic with an 6 inch duct that
should be more then enough to swap out the air.
.George