Should you repair or replace your furnace?

Three facts drive the decision: the age of the furnace, which part failed, and the repair price next to a replacement price. ENERGY STAR suggests you consider replacement once a furnace or boiler is more than 15 years old. Treat that as the point where a big repair deserves a second look. Plenty of furnaces run past it.

The repair or replace calculator scores age, the repair quote, repair history and warranty status together.

• The failed part is routine. Ignitors, flame sensors, pressure switches and capacitors are common, modest repairs.
• The furnace is well under the ENERGY STAR age mark.
• The parts warranty is still active. Heat exchangers often carry longer coverage than other parts, so check the paperwork.
• The house heats evenly and fuel bills are steady.

• A cracked heat exchanger. The heat exchanger keeps combustion gases out of the air you breathe. Replacing it is one of the largest furnace repairs, and on an older unit it rarely makes sense. Read more about a cracked heat exchanger before you agree to anything.
• Frequent repairs and rising energy bills. ENERGY STAR lists these together as a reason to replace.
• Rooms that are too hot or too cold, or a system that has become noisy. These are also on the ENERGY STAR list. Uneven heat can be a duct or sizing problem, so ask the contractor to check before blaming the furnace.
• Major parts failing out of warranty. A control board, inducer motor and blower motor failing one after another points to a furnace wearing out as a whole.

A red tag. If a technician or the gas utility shuts the furnace off as unsafe, ask for the finding in writing, including what was observed and how. You are entitled to a second opinion from another licensed contractor before you buy a new furnace.

An old furnace with a cheap fix. Age alone does not condemn a furnace. If the repair is minor and a technician finds the heat exchanger and venting sound, repairing it is reasonable. The guide on how long a furnace lasts explains what wears one out.

It failed in a cold snap. Emergency timing weakens your bargaining position. Space heaters used safely can buy a day or two to collect a second quote. Do not use an oven or a grill for heat.

Replacing the AC at the same time. The furnace blower moves air for the AC too. If both are old, pricing them together can save on labor compared with two separate jobs.

You cannot inspect a heat exchanger, test gas pressure or check venting yourself. Ask the technician for a written diagnosis naming the failed part and the test that showed it. For a heat exchanger finding, ask to see the crack or a photo of it.

Get the repair price and a replacement price in writing. A replacement quote should list the model, the heating capacity in BTU, the efficiency rating, venting changes, permits and the labor warranty. The guide to furnace replacement cost shows what drives the price.