Ductless mini splits in Vienna.

Windover Heights, the Town’s historic district in northwest Vienna, is a single-family neighborhood the Town says has changed little since the turn of the century, mostly older homes on meandering, tree-lined streets. A house from that era may have been built for radiators, with no ducts at all, and a mini split cools its rooms without cutting plaster for duct runs. The catch is outside: the Board of Review looks at major exterior changes the street can see, so the outdoor unit and line set belong on a side or back wall.

Past the district, about two in ten homes in the Town went up before 1960. Many have grown since: an addition off the back, a sunroom, a screened porch closed in. The Town reviews that work on its small-scale residential permit, on top of the county’s, and the ductwork rarely grew with the house. A new branch off the old trunk starves the rooms already on it, so the new room gets a head of its own.

Basements are the other Vienna ductless room. Finishing one inside the town goes through the Town’s review, which asks for a floor plan naming each room’s use, and a bedroom or office down there seldom gets enough air from a trunk sized for the floors above. In the rebuilds, a quarter of the Town’s homes, it’s often the far end instead: a room over the garage at the end of the upstairs system.

Out back, the Town doesn’t review a one-story shed or studio of 256 square feet or less, the county’s rules aside, and that’s where a backyard office tends to land. One head and an outdoor unit set against the building handle it, fed by a circuit from the house panel. On the Tysons edge, where three in four homes in that Census area are condos and apartments, the first call goes to the association.