I'm not an expert, but from what I've read, you're right, that's not going to be enough. If you haven't already, why don't you ask on some of the GW building forums also to improve your chances of getting this answered before the contractor gets there tomorrow :) Here is some info I've saved from our master bath remodel. Hope you find it helpful. If not, maybe someone else will :) Monica Venting exhaust If he is venting the exhaust into the attic air space, that's bad. Even if there are attic vents (normally gable wall louvered vent panels, or a combination of soffit and ridge vents) in the attic that allow air to move through the space. If he has the end of the duct just pointing at the attic gable vent, that's no good either. The goal is to get the moist air outside the house, not to dump it directly in the attic, or dump it near the gable vent, where air currents can keep the moist air in the attic. If he is bringing the duct up into the attic, then continuing the duct laterally and running the duct out through the gable wall and installing a vent cap out there, then that's a good thing. I prefer the vent to be rigid metal instead of the flex duct, and I prefer the lateral run to be sloped slightly lower as it runs towards the gable wall. I use aluminum tape to tape all seams in the duct, taping both the seam that runs the length of each piece of duct as well as around the circumference where two pieces are joined together. This way if there is any condensate in the duct it runs out the vent instead of pooling and/or running back down into the fan. It's a small, but important detail. Personally, I prefer as few holes in the roof as possible. Mongo Rigid ducts are fairly easy to slope, they just need periodic support along the horizontal run. In a attic it can either be hangers coming down off the rafters, or wood scabbed to the floor joists running up vertically. Oooooh. I didn't think of a brick house. Brick can be more difficult, but it is done. Still with brick, it might actually be easier to go out the roof, but hopefully only if it's on the back side of the house. I'm not certain if venting to the outside is required by code in your area, you could give your local building department a call. If it is a code requirement (it is in my locale), then it should have been included in the scope of the work. After all, he should bid the job and complete it to code, right? Then again, I wouldn't want a ticked off contractor cutting a hole in my brick wall or in my roof while angry and while trying to do it on the cheap.

Unless your bathroom is 21' x 21' or equivalent a 250cfm fan is way too much. Bathroom exhaust fans should be sized for 4 complete air exchanges per hour. You begin by multiplying length x width x height to determine the total number of cubic feet in the room, then multiply by the desired number of air exchanges per hour. The result will tell you the number of cubic feet of air per hour that you must move. You then divide the cubic feet per hour by 60minutes/hr to determine the required CFM. By example, let us consider a bathroom that is 10' x 10' with an 8' ceiling. 10'x10'= 100sq.ft 100sq.ft x 8' for the ceiling = 800cu/ft in the room. We desire 4 air exchanges per hour so we multiply 800cu.ft x 4 = 3200cu/ft per hour. Dividing 3200cu/ft per hour by 60min/hr = 53.3cfm. Thus a fan that is rated at 54 to 60cfm would give you the required 4 exchanges per hour.

A bathroom exhaust fan should produce 4 air exchanges per hour. Your bathroom is 7 x 7 which is 49sq.ft Assuming an 8' ceiling the total volume would be 49 x 8 = 392cu.ft We want four complete air exchanges per hour so that would be 392cu.ft x 4 = 1568cu.ft per hour. There are 60 minutes in an hour so we divide 1568 by 60min and it equals 26.13cfm. You currently have a 50cfm fan, which is twice the size you really require yet your having problems with the mirror fogging up. I suspect your problem is not the fan. Nature abhors a vacuum therefore a fan cannot push air out of a room unless there is provision for an equal amount of air to enter the room. You can test the theory by running the shower and leaving the bathroom door slightly ajar to allow more air to enter the room. Generally they make a slightly higer gap under the bottom of a bathroom door to allow more space for makeup air to enter the room but in some circumstances that does not provide enough makeup air. The solution then is to install a duct through the wall to an adjacent room and put a grille on either side. That will allow the additional air.

Our very tiny master bath (40 square feet) doesn't have one and never did. There is a big viga running across the ceiling in this bath, so I'm not sure where a fan would go if I wanted one (I would consider one of those remote units like pal has, but we have a flat roof with no real space between roof and ceilings). The room has a window, though, which helps. There is a newer combo heat/fan/light unit in the main bath. Neither bath has ceiling light fixtures, so there is no competition.