Furnace replacement in Philomont.

Propane warms about 42 percent of owner homes in the Purcellville ZIP area that Philomont’s Census numbers come from, against about 6 percent for natural gas. So a new furnace here is more often a propane furnace than a gas one. $4,285 to $14,040 is the installed range for either, 2 to 5 ton, keeping the air conditioner you have, and the HVAC replacement cost estimator at goswiftpro.com/estimator narrows it to your house.

The median owner home in that ZIP area dates to 2000, so a furnace original to it is well into its third decade, past the years most are retired. Nearly three in ten homes date from 1980 through 1999, and roughly a quarter predate 1980. In houses like those the furnace may be older than the air conditioner beside it, which is the case a furnace on its own suits best.

Winters set the stakes. The Purcellville station counts 4,942 heating degree days a year and 114.7 days with lows at or below 32F, and the coldest nights of the January 2026 arctic outbreak fell under Extreme Cold Warnings. A furnace that fails in that stretch leaves a house that cools fast. The median spring date of the last 32F low is April 16 and the fall’s first is October 25, which bracket the mild weeks for planning a swap.

Permits come into it. Loudoun County asks for one when a gas furnace is swapped, and since October 2025 it has skipped plan review for a like-for-like replacement, same BTUs and same location. Read the input rating off the old nameplate, then ask for the new one’s, and compare the two. Oil heats about 6 percent of owner homes in the ZIP area. That burner is one we won’t touch, though trading oil for propane or a heat pump is a job we can price.