When to Repair vs. Replace Your Furnace

Your furnace breaks down on the coldest night of the year. The repair quote comes in, and you’re left wondering: should I fix it, or is it time for a new one? Here’s how to make that decision.

The 50% Rule—If the repair costs more than 50% of a new system, replace it. This simple guideline accounts for the fact that an aging system will likely need more repairs soon. A $2,000 repair on a 15-year-old furnace is almost never worth it when a new high-efficiency unit starts around $4,000–$5,000 installed.

Age Matters—A well-maintained gas furnace lasts 15–20 years. If yours is 15+ years old, you’re in the replacement zone regardless of the current repair. Parts become harder to find, efficiency degrades, and the risk of heat exchanger cracks increases. A cracked heat exchanger is both a safety hazard (carbon monoxide risk) and typically costs more to repair than the furnace is worth.

Efficiency Gains Are Real—If your furnace is 80% AFUE (common for units installed before 2010), upgrading to a 96% AFUE unit means 16% of your heating energy is no longer going up the flue. On a $200/month gas bill, that’s $32/month in savings—nearly $400/year. Over 15 years, that’s $6,000 in energy savings alone.

Safety Red Flags—Replace immediately if the heat exchanger is cracked, you detect carbon monoxide near the furnace, you see visible soot or flame rollout marks, the furnace produces a yellow or flickering flame instead of a steady blue, or you smell gas when the furnace runs.

Repair Makes Sense When—The furnace is less than 10 years old, the repair is minor (ignitor, flame sensor, blower motor capacitor), the system is properly sized for your home, and it’s been well-maintained with regular filter changes and annual tune-ups.

Don’t Forget the Ductwork—If you do replace it, it’s the perfect time to evaluate your ductwork. Leaky, undersized, or poorly designed ducts can waste 25–40% of your system’s capacity. A new furnace connected to bad ductwork won’t perform to its potential.

Not sure where your furnace stands? Our free HVAC guide helps you assess your system’s condition. Or schedule a diagnostic—we'll give you an honest assessment with repair and replacement options side by side.