Ductless mini splits in Dunn Loring.

The Census counts 862 homes from the 1960s across the whole Dunn Loring area, its biggest decade, and at most 32 of them have a 22027 address; the rest carry Vienna mail. Sixty years on, a lot of those houses have grown: a family room pushed out the back, a porch closed in, a carport made into a den. The 1960s ductwork seldom grew along with them, and a branch tapped off the old trunk to feed the new room steals air from the rooms already on it. A head with its own outdoor unit serves the new room and leaves the old system alone.

Inside 22027 the houses are younger and almost all detached, 608 of 659, with the 1990s the busiest decade. A house from those years nearly always came with central air, so a mini split there is usually for space finished later: the room over the garage at the far end of the upstairs ducts, or a basement turned into an office that the thermostat a floor up never feels.

Whatever room it serves, the head has to heat as well as cool. Vienna’s weather station, 3.6 miles west, records about 99 nights a year at or below freezing and close to four at 10 degrees or below, and Fairfax County saw Extreme Cold Warnings on three nights between January 27 and 31 of 2026. If the room has no other heat, choose a model rated to keep heating at those temperatures, and size it for January as much as July.

Then there’s where the outdoor unit goes. The Vienna station averages about 18 inches of snow a year, and storms like January 2019’s, which left 12 inches near Tysons Corner next door, bury anything set flat on the ground. A wall bracket or a raised stand keeps the coil clear and lets defrost water drain instead of freezing underneath.