Chelmsford lies southwest of Lowell across the town line, with an older centre, post-war neighbourhoods and newer construction toward Route 3 and the 495 corridor. The newer houses tend to carry high-efficiency condensing furnaces with sidewall venting and sealed combustion, while the older ones still run conventional chimneys.
Both need different things from a visit. Condensing equipment lives or dies on its condensate trap, drain and vent slope, and a frozen or debris-blocked trap in January shuts the furnace down. A conventional furnace depends on a flue that can still draft, which is a chimney question as much as an equipment one.