Furnace replacement in Alexandria.

Gas heat isn’t spread evenly across an Alexandria address. Out in the county, Hayfield has close to nine in ten owner homes on gas and Fort Hunt about eight in ten, with Rose Hill, Groveton and Hybla Valley each near three in four. Inside the City it’s a bit under six in ten, and in Franconia and Woodlawn, where most owners heat with electricity, a furnace is the exception.

Keeping the air conditioner makes the most sense in the older corners. A Fort Hunt house from the early 1960s or a Belle Haven one from the 1950s usually keeps its furnace in the basement, while the condenser outside is often the part somebody already swapped in a hurry one July. Read the date on both labels. An air conditioner younger than ten or so, on R-410A or a newer refrigerant, is usually worth keeping; one still on R-22 is the case for pricing both at $8,898 to $23,000.

A high-efficiency furnace changes the outside of the house in one small way: its plastic vent pipes usually leave through a wall instead of the chimney. In Old Town the Board of Architectural Review looks only at what people can see from a street or public place, and its staff can approve a vent under a cubic foot if its color matches the wall. Out a side or back wall nobody sees from the street, the Board isn’t involved at all.

Kingstowne went up mostly in the 1980s and 1990s, and close to half its homes are townhouses, so plenty of furnaces there sit in a closet or an attic built around the first one. Hybla Valley has the most propane on the Alexandria address, roughly one owner home in twenty-two. A propane furnace swaps out the same way; only the gas valve gets set for propane.