"Odor free" does not mean healthy. There is no substitute for proper ventilation. First of all, effective ventilation is dependent upon several things. First, you must have the same amount of clean air coming in as you exhaust out, obviously from some kind of light-tight inlet. Second, friction in the air exhaust ducting is just like having too small a garden hose, or a kinked one. That too has to be light-tight. Third, fan rating needs to be at least double the theoretical value due to both duct friction, and even more, pushing against hydrostatic pressure in damp or humid atmospheric conditions. Fourth, air is more efficiently pulled than pushed. A weatherproof exterior-mounted fan will extract air better as well as isolate the noise. Intermediate in-line duct fans are a second best. Worst are the old-fashioned noisy indoor ceiling propeller fans.
Very quiet efficient inline fans cost three or four hundred dollars. Most will accept variable-speed controls, another nice feature. Panasonic makes an especially nice line of them. More ordinary bathroom quiet fans in the 200 CFM range, for wall or ceiling mount, are about half that price. The idea with a speed-control fan is that you can run it low most of the time, then boost the CFM when mixing nasty chem, or when fighting greater hydrostatic pressure during wet weather. 100 CFM is generally too small to be realistic. Broan probably still has a selection of outdoor-mounted pull fans, which provide more CFM for less money.
Among the many things our company sold to construction before I retired were thousands of ventilation fans a year. Even though darkrooms were a minor percentage of that, I consulted on many darkrooms every year, all the way from tiny bathroom conversions to huge industrial labs using ventilation fans so large that they required three-phase motors. A good placed to review options is a Grainger catalog (their website is so-so). Forget the toy stores like Lowes or Home Cheapo. Nobody in those places has a clue about any of this.
