Whole-home humidifiers in Aldie.

Nearly every owner home in the 20105 ZIP went up after 2000, so there are no drafty farmhouses to chase here. What changes from one Aldie house to the next is size. A Willowsford house with three or four thousand square feet often runs two or even three heating and cooling systems, one per level or wing, and a humidifier only treats the air its own furnace moves. Put one on the basement system and the upstairs bedrooms can still be zapping you at the light switch.

So the first thing we ask is which system serves the rooms where you feel it. Often that’s the one over the bedrooms, up in a utility closet or attic, and getting a water line and a drain there is the real job. Sometimes two smaller units beat one big one. We would rather tell you that at the kitchen table than hang one on the wrong furnace.

About three in four Aldie owners heat with gas, so a bypass model on a gas furnace is the usual answer, and one in seven runs electric heat pumps, where a fan-powered Aprilaire does better with the cooler air. Propane is a small slice, around one in twenty, and those furnaces behave like gas for this purpose.

Stone Ridge has townhouses and condo communities, each with its own management company, and a condo association can have opinions about a new water line through a shared wall. Check the rules before you buy. A detached house in Kirkpatrick Farms or Stone Ridge has no such question, just the shortest clean run from the furnace to a cold-water pipe. If a unit you already have stopped, the $99 visit finds out why.