I have 2 bathrooms and a kitchen that are currently unvented. I would like to install an inline exhaust fan to service all three. I will be putting the exhaust fan just inside a gable that will have an exhaust port to the outside. Are there any issues with having a kitchen and bathroom share exhaust ducting? They will all have dampers at the intake vent. See picture for diagram. I have already calcuated the CFM needed for the kitchen which will be about 360 CFM and will be getting an appropriate fan. Are there any issues, safety or otherwise, with the sharing of the ductwork? Grease buildup?
International Mechanical Code 2012
Chapter 4 Ventilation
Section 401 General
401.1 Scope. This chapter shall govern the ventilation of spaces within a building intended to be occupied. Mechanical exhaust systems, including exhaust systems serving clothes dryers and cooking appliances; hazardous exhaust systems; dust, stock and refuse conveyor systems; subslab soil exhaust systems; smoke control systems; energy recovery ventilation systems and other systems specified in Section 502 shall comply with Chapter 5.
Chapter 5 Exhaust Systems
Section 505 Domestic Kitchen Exhaust Equipment
505.1 Domestic systems. Where domestic range hoods and domestic appliances equipped with downdraft exhaust are located within dwelling units, such hoods and appliances shall discharge to the outdoors through sheet metal ducts constructed of galvanized steel, stainless steel, aluminum or copper. Such ducts shall have smooth inner walls, shall be air tight, shall be equipped with a backdraft damper, and shall be independent of all other exhaust systems.
Chapter 4 says you cannot use the same ducting for ventilation, as you do for your range exhaust. Chapter 5 is quite explicit in what materials should be used for the range exhaust ducting, and also says that the ducting cannot be shared. If you're using the ventilation ducting between two or more spaces, you'll have to be sure the fan and ducting are both adequate to move the amount of air required. you'll also have to insure there is an adequate supply of makeup air.
NOTE: Local codes may vary. Contact your local government for all applicable codes.