Furnace replacement cost: gas, electric, oil

The ranges below are national figures published by This Old House, which says they are based on HomeAdvisor estimates.

Electric furnaces are the simplest to install because they need no gas line or flue. Gas furnaces need safe venting and a gas connection. Oil furnaces also involve a tank and a chimney or vent in good condition, which is part of why they sit at the top of the range.

• Efficiency. According to This Old House, the U.S. Department of Energy defines a high-efficiency furnace as one with an AFUE of 90% or higher. These condensing furnaces cost more and need plastic vent pipes and a condensate drain, which can add labor if your old furnace vented into a chimney.
• Size. This Old House gives a typical size range of 40,000–120,000 BTU. The right size comes from a heat-loss calculation on your home.
• Blower and burner type. Two-stage and modulating burners and variable-speed blowers add comfort and cost.
• Venting, gas line and electrical changes. Any of these adds labor and materials.
• Duct repairs. A new furnace on leaky or undersized ducts will not perform as rated.
• Access. Attic and crawlspace furnaces take longer to replace.

This Old House gives a simple rule: a repair is generally worth doing if it costs less than half the price of a new furnace. The same source cites a typical furnace lifespan of 15–25 years and notes that breakdowns become more frequent from around 15 years.

A cracked heat exchanger is the main exception to weighing costs. It is a safety problem, and on an older furnace it usually ends the discussion in favor of replacement. The guide on whether to repair or replace your furnace covers the decision in more depth.

If you are replacing anyway, it is worth a look at heat pump versus furnace running costs for your climate before you commit to the same fuel.

Ask for a written quote that lists:

• The exact model numbers and capacity of the equipment or part being installed.
• Labor, materials and refrigerant listed as separate lines.
• Permit and inspection fees, and who pulls the permit.
• Removal and disposal of the old equipment.
• The parts warranty and the labor warranty, each with its length in writing.

Check that the quote names the AFUE rating and the BTU input, states how the furnace will be vented, and says whether a combustion safety test is done after installation. Get at least three quotes for the same size and efficiency so you are comparing like with like.