Lighting, Light Fixtures, Ceiling and Exhaust Fans - Venting exhaust fans

I need to put fans in 2 bathrooms and 2 kitchens so I'm planning out the paths for the vents. I could knock 4 separate holes in the exterior walls for the 4 vents, but that seems like a lot of damage when there is an alternative staring me in the face.

There is an unused brick chimney which used to connect to something, maybe an oven, or a wood-fired stove, or something. It is no longer connected to anything. There is no fireplace or anything connected to this chimney-type thing. It's not even a fireplace chimney, it's just a brick path leading from the main floor kitchen to the 2nd floor kitchen. There's one round hole in the brick in the 2nd floor kitchen and a large gap in the first floor kitchen wall directly below it.

I would like to use this path to vent the kitchens and bathrooms. Why? Because it's already there and it's taking up space for nothing. I might as well try to find a use for it. The wall juts out to cover up this path.

So my plan is to run vents through the ceiling from the 1st floor bathroom and kitchen, connect them inside the chimney with a Y-connector which connects to a tube which goes up the chimney to the 2nd floor kitchen, where vents from the 2nd floor bathroom and kitchen will join the tube. Then the tube will be vented out through a new hole I will cut in the brick on the other side of the hole (shown in picture)

I would like to know if my plan is completely stupid and will cause damage to the home. I've been reading about venting and the only issues I can find are:
1. You should use insulated tubing.
2. You should use Y-connectors instead of T-connectors.
3. You don't want to vent out of a soffit because then the steam would just re-enter the attic.
4. You want the exit vent to run at 45 degrees, not straight up and not straight horizontally.

Another thing that is confusing me is how to get the vents from the 2nd floor bathroom and kitchen to enter the hole in the wall from the ceiling. I would have to run these vents down from the ceiling to get into the hole. I assume this is probably not recommended but I don't know enough about this subject to know exactly why. Moisture buildup? There would be motors on the fans to force the steam out of the hole - to the average person who doesn't do this for a living, a motor sounds like it would be enough. I'm probably wrong.

I'm just trying to find the best solution which will cause the least damage to the outside of the home while still venting these 4 rooms properly and according to code.

http://lh5.ggpht.com/_CLHSTuEIMns/SYip7RBjBII/AAAAAAAAAHw/dAB7Y-00B2I/s400/100_2059.jpg (http://picasaweb.google.com/lh/photo/4JvEcLgvuomIe6lF8dzrYw?feat=embedwebsite)

In the picture, the 2nd floor kitchen vent would be coming from the right (from the ceiling, then down outside the brick and into the hole); the 2nd floor bathroom vent would be coming from the left (probably through the ceiling and down outside the brick and then into the hole). These pipes would be covered up by a wood and drywall frame or cabinetry. The vents from the 1st floor would join them inside the hole.

I think the issue will be with the length of the duct runs and the distance in the chimney. Bath and kitchen exhaust fans are not very powerful and the longer the duct the less efficient they will be.

Kitchen grease will also build up in the ductwork.

... my plan is to run vents through the ceiling from the 1st floor bathroom and kitchen, connect them inside the chimney with a Y-connector which connects to a tube which goes up the chimney to the 2nd floor kitchen, where vents from the 2nd floor bathroom and kitchen will join the tube.

Sorry, prohibited as described by:

IRC M1507.1 Where toilet rooms and bathrooms are mechanically ventilated, the ventilation equipment shall be installed in accordance with this section. M1506.2 Recirculation of air. Exhaust air from bathrooms and toilet rooms shall not be recirculated within a residence or to another dwelling unit and shall be exhausted directly to the outdoors. Exhaust air from bathrooms and toilet rooms shall not discharge into an attic, crawl space or other areas inside the building.

and

IRC M1502.1 General. Range hoods shall discharge to the outdoors through a single-wall duct. The duct serving the hood shall have a smooth interior surface, shall be air tight and shall be equipped with a backdraft damper. Ducts serving range hoods shall not terminate in an attic or crawl space or areas inside the building...

Bold is mine.

Thus combined vents from standard exhaust fans are prohibited, reasoning is that air from one bathroom or kitchen will back up into other rooms on the combined line - the "flappers" at exhaust fan housings are not air tight - and you will get kitchen smells in the bathroom and bathroom smells in the kitchen. :( (There are exception for engineered systems in multi-unit buildings, but they don't apply in your case.)

However... you could combine the two baths on one exhaust line if you use a remote fan which pulls air out of the bathrooms, for example one of the Fantech (http://www.fantech.net) products

http://www.fantech.net/bath17.jpg

as air pulled toward the fan will not back-flow from one bathroom to the other.

Also, your local building department might let you combine the two kitchen exhausts in a similar manner.

However... you could combine the two baths on one exhaust line if you use a remote fan which pulls air out of the bathrooms, for example one of the Fantech (http://www.fantech.net) products

http://www.fantech.net/bath17.jpg

as air pulled toward the fan will not back-flow from one bathroom to the other.

Also, your local building department might let you combine the two kitchen exhausts in a similar manner.

Hmm.. it would probably be too tricky to get one of those motors shown in the picture into position to serve both vents. I had been assuming the motor would be located inside the vents, not remote.

So I guess I will vent all 4 rooms separately, close to each vent.

Thanks for the details!