Inline fan to a soffit vent

[RascalHoudi]

I am in Ontario, so need to deal with hot summers and cold winters.

I have built an addition, and the master bathroom will have a whirlpool tub. Additionally, the custom tile shower will have a steam generator. Bottom line.. lots of moisture.

My square footage calculations came out to a requirement of a 112cfm fan. I purchased a 190cfm inline fan and will mount it in the attic about 3 feet above the bathroom ceiling. I am putting an adjustable vent in the shower, and another one in the main bathroom. They will be T-Y'd before the horizontally mounted inline fan in the attic. From there the ducting will slope downward to the soffit and exhast through a soffit vent on the southwest corner of the building (this will get lots of winter sun should there be any ice buildup in the soffit exhaust). All piping is 4" insulated.

I have a back draft damper and wondered where the best place is to install it. I'm not worried about putting it on either of the intake pipes, since the fan will draw from both locations at once, so I will put it between the fan and the soffit vent to prevent any backdraft from outside. If I put it close to the fan, it will be easier to install and service. Unless there is some benefit to putting the damper right at the soffit vent?

Also.. I selected a timer switch for the fan that goes up to 30 minutes. Think that is sufficient time?

thx.