Air duct cleaning in Catlett.

Electricity heats about half of Catlett’s owner homes, usually through a heat pump, which sends heated and cooled air through the same ductwork. At the Warrenton co-op station, about seven miles west-northwest, a normal year runs close to 4,700 heating degree days against roughly 1,000 cooling degree days, so most of the blower’s hours come in winter. Between the median first freeze on November 1 and the last one on April 9, a heat pump runs long, steady cycles, each one drawing the house’s air, dust and all, back through the returns.

Wood is the third fuel in 20119: 131 owner homes, about one in eight, heat with it. Loading a stove or emptying its ash pan lifts fine ash into the room, and in a forced-air house the returns pull part of that into the ductwork. Where a house burns wood, the return side is the first place to send the camera, because that’s where ash would settle.

Roughly 180 of the ZIP’s homes predate 1940, and the historic village counts buildings from 1855 to 1958; the oldest went up long before anyone ran ductwork. What they have now was added later, threaded through closets, crawlspaces and attics, often in flexible duct that sags where its straps have let go. The roughly 470 houses from the 1990s and 2000s have the ducts their builder laid out, and a 1990s system that’s never been opened has moved thirty winters of air.

The County’s plan puts Catlett in a nearly flat basin with extensive floodplain along Cedar Run, and the Weather Service gauge near the village crested at 18.2 feet in July 2013, when flash flooding closed roads in Catlett. Ducts in a crawlspace or basement that took water are a different job from dusty ducts. We photograph them first; anything that sat in floodwater may need replacing rather than cleaning, and the photos show which.