Inevitably on This Old House, we run out of air time and end up giving less than full coverage to a noteworthy technology or product that goes into one of our subject houses. Usually this happens towards the end of a project, when the air is thick with incoming goods and we have to pick and choose those that we will focus on. A key product that was only glancingly referred to in the Key West job is a so-called in-line ventilation system. Ducting runs from bathrooms, showers and even vent hoods to a remotely located fan, which exhausts to the outside. Advantages include near-silent operation, powerful venting and especially long-lived motors. Savannah homeowner Mills Fleming, whose house has three bathrooms serviced by such a system, reports that his father, when paying a visit, always claims that "the darn vent isn't working." "He expects a roaring bathroom fan like he's used to," Fleming says, "I have to show him the fogless mirror to convince him." Sized according to the cubic feet of air needing to be removed, these systems use insulated, flexible ducts with fan motors matched to the load. The manufacturer used in Key West has a line that starts with 4" ducts with a small fan that pulls 108 cubic feet per minute and ranges up through 5", 6", 8", and 10" to the 12" diameter 2019 cfm monster Michael Miller specified for servicing the range hood in the Key West kitchen. "We needed good ventilation for removing humidity in the bathrooms and cooking odors in the kitchen," Miller says. "I'd never used a system like this before, but after hearing how quiet they are, and powerful, I've already put one into a job I'm designing now." The key to the system is the fan motor, located away from the room being vented. In Savannah, the motor was hung in the attic, as was the kitchen fan in Key West. The Key West bathroom fans were hung underneath the building. In either case, the sound of sucking air is barely perceptible. The motors are made in Europe and feature external rotors, meaning that there is no drive shaft; rather, the fan blades turn around the motor itself, just like a ceiling fan. Starting at around $120 for a small unit (versus less than $100 for a good-quality traditional ceiling-mount fan), the systems become cost-competitive as multiple rooms are serviced by a single motor. Most commonly, two bathrooms vent through one motor; when the fan is activated in one bathroom, the other bathroom is vented as well. Cambridge architect Chris Dallmus specs such systems for nearly all of his firm's projects. "When you think about the benefits in terms of longer paint and wallpaper life, less mold and mildew and plain and simple quietness, these things are great." That's what Mills Fleming keeps telling his dad.