Don't know if this is an electric or mechanical question, but here is my problem ...

we have a 60's brick ranch house that we are remodeling ... one story with a full basement ... it has 2 small baths that stack on top of each other, both on the back wall of the house ... the exterior wall on the top bath is brick veneer on wood frame and the the exterior wall on the lower bath is 10" concrete block ... now, the issue we have ...

neither bath has an exhaust fan ... I don't want to just exhaust the upper bath into the attic space and going through the brick wall to the outside would be a pain; however, going into the attic and piping to the soffit (we have a fairly wide overhang) seems like a reasonable solution ... but, what about ...

the lower bath? ... the only options I can come up with to vent to the outside is to go through the concrete block (ugh!), go into the space between the two floors and then through the brick wall above (not easy either), or lastly ...

go up and through the upstairs bath and tie into the exhaust pipe in the attic (in other words, share the same exit pipe with the upstairs bath) ... this could be done fairly easily since both baths are currently torn down to the studs ... my question is ...

can or should this be done? ... I've never seen it done before ... it's a long way for the exhaust to go up and out from the lower bath to the soffit on the upper floor ...

any ideas or suggestions about how to solve this exhaust challenge? ...

if my idea makes sense, how should I size each of the exhaust fans? again, both baths are small (about 6' x 8').

Thanks in advance, Bill

The fans can be in the 80 to 100 CFM range for those baths. Taking the lower bath fan up through the upper bath and to the soffit is OK, but connecting the two into one duct is more complicated. If that is done, there needs to be a backdraft damper in each duct before they connect, and the exit duct needs to be bigger in diameter and sized properly...and then you'll need a vent cap which is sized for the larger duct. If you run them to the soffit independently, then yes, you'll have to cut two holes, but everything can be done with the fan manufacturer's standard fittings for each fan. I forget how to calculate static pressure, but the lower fan should be checked for the manufacturer's design maximum static pressure. Calculating it involves allowing for the amount the fan must lift the air, plus allowances for friction loss for each elbow fitting in the ductwork. Perhaps one of the mechanical contractors will post a how-to on that issue. It is remotely possible that you may have to use a more powerful fan for the lower bath because of the static prseeure in such a long and convoluted duct run.