Furnace Repair & Installation in Portland, Maine

A gas or oil furnace combines a burner, a heat exchanger, a blower, a set of safety controls, and a flue — all in one box, and a failure in any one of them can look identical from the thermostat's point of view. A cracked heat exchanger, a failed igniter, a clogged filter starving the blower, and a tripped high-limit switch can all present as "the furnace won't turn on," but they're entirely different repairs.

This is why a real diagnostic checks the whole chain in order rather than guessing at the most common part.

Annual Fuel Utilization Efficiency (AFUE) measures how much of the fuel burned actually becomes heat in your house versus what escapes up the flue. A mid-efficiency furnace runs around 80% AFUE; a high-efficiency condensing furnace recovers additional heat from the exhaust gas — cool enough by the time it's captured that it condenses, which is where the "condensing" name comes from — and can reach the mid-90s.

• A dirty or wrong-size filter, changed too rarely — restricts airflow, makes the blower work harder, and can overheat the heat exchanger over time.
• Short-cycling from an oversized unit — more on-off cycles per hour wears ignition components faster than a correctly sized system running longer, steadier cycles.
• Skipped annual service — burner and heat-exchanger inspection catches early cracking and combustion problems before they become a safety issue or a mid-winter failure.
• Closed-off supply registers in unused rooms — this raises system pressure and can shorten blower motor life, contrary to the popular belief that it saves energy.