Furnace tune-ups in Midland.

Of the 1,066 owner homes in ZIP 22728, the Census counts 354 heating with propane and 12 with utility gas, so a Midland furnace that burns fuel usually burns propane from a tank on the property. Propane runs at close to three times natural gas’s pressure at the gas valve, through smaller burner orifices. The tune-up reads that pressure with the burners lit and checks it against the propane figure on the rating plate, where a furnace set up wrong at install shows itself.

The other 622 owner homes heat with electricity, usually a heat pump with electric strips in the air handler for backup. NOAA’s 1991 to 2020 normals for Warrenton 3 SE, about six miles north-northwest, count close to 13 days a winter when the high never gets above freezing. On those days a heat pump gets no warm afternoon to catch up; it runs, defrosts and hands more of the load to the strips. Its tune-up is the same $69 a system and runs heat, the defrost and each bank of strips before the first freeze, which that station’s median puts at November 1.

That station sits around 500 feet up, above the village’s 327, so read its numbers as close, not exact. Fauquier County’s code sizes heating for a 17 degree night; the station averages about five nights a winter at 10 or colder and one at zero or below every two or three years. It read 2 degrees on February 20 and 21, 2015.

The railroad-era village houses were built long before anybody set a furnace in a cellar, so their heat came later: a basement furnace, a heat pump with attic ducts, a ductless mini split. A boiler or a ductless system gets the tune-up at the same $69 a system.