Air duct cleaning in Clifton.

Six in ten homes in 20124 have nine rooms or more, more than twice the Fairfax County share. A house that size usually has more than one trunk and often a second system, one serving the main floors and one the upstairs or the basement, and each system gets its own camera photos and its own line on the price. And in the Census tract around the town, 98 in 100 homes are detached houses, so every trunk, branch and return is the owner’s to look after; there’s no association shaft or shared riser to work around.

Nearly eight in ten Clifton homes went up between 1980 and 1999, so most systems still run on their original ductwork, three or four decades of returns pulling air through the same metal. In the 1980s subdivisions around Springstone Drive the furnace usually sits in the basement, with the main trunk hung under the first-floor joists. In the bigger houses on the acreage the second system often lives in the attic, where a flexible run can sag between the joists or get pinched under a box someone stored on it.

Inside the Town of Clifton the houses are mostly from the decades around 1900, built long before forced air. Their ductwork went in later, fitted into crawlspaces, closets and attics wherever it would go, and the Town’s own plan says the restoration work there started in the 1970s and hasn’t stopped. Sanding and plaster work with the system running sends that dust wherever the returns pull it, and the camera photos show how far it went.

A big house can also mean a long dryer vent, from a laundry room in the middle of the floor plan to an outside wall. Added to an air duct cleaning, the dryer vent cleaning is $199.