Air duct cleaning in Lovettsville.

Lovettsville’s weather is a heating story. At the Purcellville co-op, the nearest long-running station, January nights average a low of about 24.5 degrees, and heating degree days outnumber cooling degree days almost five to one, 4,942 to 1,050. Each hour of heat means the blower drawing room air in at the return grilles and sending it back out the supply runs, so winter is when the ducts do most of their work. Propane heats about 44 percent of owner homes in town, and electricity, usually a heat pump, about 42.

The Census dates the typical owner’s house in town to 2007, and six in ten of its homes to 2000 or later. Town Center grew around Zoldos Square after the Town approved it in 2002, alongside Keena, Loudoun West and Heritage Highlands. A house from those years usually still has the builder’s ductwork: a sheet-metal trunk with flexible branches, one or two big return grilles, and nearly two decades of filters behind them. Flex duct sags between its hangers as it ages, and dust settles in the dips. That’s what the camera finds.

Old Town is the opposite case. The 2012 National Register nomination for the Lovettsville Historic District, about 90 acres around East Broad Way and Pennsylvania Avenue, dates more than 60 percent of its historic buildings to 1880 through 1930, and balloon framing is the most common build. Central air arrived generations after those houses did, so the ductwork went wherever it could: through a closet, up an open wall cavity, across the attic. We photograph what’s in there before any price, and sometimes the answer is that there isn’t much worth cleaning.

Beyond the town limits sit about three of every four owner homes in 20180, nearly all detached houses on rural lots. A bigger house out there frequently has a second air handler for the bedrooms, tucked in the attic or a bonus room, so we walk the house before writing the number and price each system on its own. Add the dryer vent cleaning while we’re there for $199.