What's the '50% rule'?

If a repair costs more than about half of a new furnace, replacement is usually the better value. It's a OurHomeSays rule of thumb, not an official standard.

Should I replace the AC at the same time?

If both are near end-of-life, replacing together can save on labor and match efficiency — but only if the AC is also aging. Don't replace a healthy unit for convenience.

Furnace repair or replace — with the safety override

First, the override: if a technician confirms a cracked heat exchanger (a carbon-monoxide risk), replace it regardless of the repair price and don't run it meanwhile. Otherwise it's a cost decision — a gas furnace typically lasts 15–25 years, and a repair over about half the cost of a new unit usually tips to replacement. Enter your numbers below.

Typical service life used: 15–25 years (cited below).

Has an HVAC technician confirmed a cracked heat exchanger or CO risk?

furnace age (years)Breakdowns in the last 12 monthsRepair quote ($)Replacement cost ($)

It's much less efficient than a modern unit

Tell us the age, repair quote, and replacement cost for a verdict.

When to call a pro

• Any diagnosis that involves gas, combustion, refrigerant, or the heat exchanger — get a licensed technician.

The safety override comes first

A cracked heat exchanger can leak carbon monoxide into your home. If a technician confirms one, replacement is the answer regardless of the math, and the furnace shouldn't run until it's resolved. This is the one case where cost doesn't decide — and it's why OurHomeSays keeps the safety check separate from the money.

When it's just a cost decision

A gas furnace typically lasts 15–25 years (InterNACHI). Under about two-thirds of that with a modest repair, fix it. Past that, or with a repair over ~50% of a new unit, or repeated breakdowns, replacement usually wins — and a modern high-efficiency unit lowers running cost. Furnaces made before 2010 may also face R-22-era parts issues.

When to call a professional

• Any heat-exchanger, gas, or combustion diagnosis needs a licensed HVAC technician.
• Get the crack claim in writing — 'cracked heat exchanger' is sometimes used to upsell; a second opinion is fair when the furnace is otherwise young.

Common questions

What's the '50% rule'?: If a repair costs more than about half of a new furnace, replacement is usually the better value. It's a OurHomeSays rule of thumb, not an official standard.
Should I replace the AC at the same time?: If both are near end-of-life, replacing together can save on labor and match efficiency — but only if the AC is also aging. Don't replace a healthy unit for convenience.

Sources

Gas furnace typical service life: 15-25 years. Tier 2 (standards/extension)
InterNACHI (Standard Estimated Life Expectancy Chart) · verified 2026-07-26
Gas furnace replacement: $3,500–$7,500 (US, industry estimate). Tier 3 (industry estimate)estimate · has commercial bias
Sears Home Services · verified 2026-07-26
HVAC service call / diagnostic: $70–$250 (US, industry estimate). Tier 3 (industry estimate)estimate · has commercial bias
Angi · verified 2026-07-26