South Lowell runs down toward the Billerica line, a mix of smaller houses, two-families and the industrial edges that grew along the rail and the Concord River. The housing is less uniform than the Highlands, and so is the equipment inside it.
Some houses here sit on slabs or shallow crawlspaces, which puts the furnace in a closet and the ductwork under the floor, where it is cold, damp and hard to reach. Others have full basements and a conventional layout. The first question on a call is which of the two the house is, because it changes what can be inspected and what can be corrected.