Repair vs replace calculator

Enter your situation and the calculator applies two published rules: ENERGY STAR's age guidance and the Department of Energy's repair-cost test. An optional efficiency estimate shows a rough payback for replacing.

The rules used

• ENERGY STAR: consider replacing a furnace or boiler older than 15 years, and a heat pump or air conditioner older than 10 years; also consider it if equipment needs frequent repairs and bills are rising.
• DOE flowchart (heating systems): if the system is not broken and is over 15 years old, replace. If it is broken and repairs cost more than half the cost of replacement, replace; otherwise repair. Very inefficient systems (draft-hood gas furnace, AFUE below 80%, oil boiler below 80% AFUE, all-electric resistance) point toward replacement.
• Heat pump and air conditioner: the DOE chart covers heating systems. For heat pumps we apply the same 50% repair-cost test as a rule of thumb, with ENERGY STAR's 10-year age guidance.
• Payback estimate (optional): annual savings = yearly fuel spend × (1 − current efficiency ÷ new efficiency). This is an approximation that ignores duct losses, fuel price changes and rebates. The DOE guide's own example is about $320 per year saved on a $1,000 fuel spend when going from 65% to 95% AFUE.

Before deciding, have a licensed contractor check safety items the DOE lists for a furnace tune-up, such as flue gas spillage, the vent connector and chimney, and heat exchanger cracks or leaks. If a technician finds a cracked heat exchanger, follow their advice about using the furnace. See our guide repair or replace your furnace.

Frequently asked questions

What is the 50% rule?

The U.S. Department of Energy's repair-or-replace flowchart for heating systems asks, for a broken system, whether repairs will cost more than half the cost of replacement. If yes, it says to replace; if no, to repair.

How old is too old for a furnace?

ENERGY STAR says to consider replacement if a furnace or boiler is more than 15 years old, and a heat pump or air conditioner more than 10 years old. The DOE flowchart also uses 15 years for heating systems that are not broken.

Is this a recommendation to buy a new system?

No. It applies published rules of thumb to your numbers. A licensed contractor should inspect the equipment, check the heat exchanger and venting, size the replacement properly and give written quotes.

Sources

• When is it time to replace? (ENERGY STAR)
• Building America Best Practices Series Vol. 14: Energy Renovations, HVAC (repair or replace flowchart) (U.S. Department of Energy)

General guidance, not a quote or inspection. Disclaimer.