AC tune-up in Haymarket.

Inside the town limits an air conditioner isn’t supposed to be on display. The Town’s historic district guidelines want outdoor heating and AC units screened from public view, and where planting does the screening it has to work all year. That means evergreens, and evergreens keep growing. A condenser pulls air in through the coil on its sides and pushes it out the top, so a hedge grown to within a few inches leaves it breathing its own hot air. The tune-up cleans that coil, and the tech tells you if the screen needs cutting back.

The houses behind those screens date mostly from the 1980s and 90s, around a 1995 median, and close to four owners in ten heat with electricity. In a house that age that usually means a heat pump, so the unit you call the air conditioner has been heating since November. In the Town’s townhouses, about a third of its homes, the indoor half often sits in a hall closet or the attic, with a drain line nobody thinks about until a ceiling stain shows up.

Outside the town, close to half of all Haymarket homes were built from 2000 to 2009 and three in ten more since 2010. A big two-story house from the first wave in Dominion Valley or Piedmont often runs a second system for the bedrooms, its air handler up in the attic, the hottest room in the house all summer. Each system is its own tune-up at $99, and the attic one is the one that gets skipped.

Bull Run Mountain Estates is older and all single-family, with a 1978 median owner home. Where a propane furnace heats one of those houses, about one in eight up there, the cooling coil sits on top of it and shares its blower and filter, so the tune-up starts indoors before it goes out to the condenser.