The repair-vs-replace call on a 12-year-old system with a $1,400 quote is genuinely hard — and HVAC companies have an incentive to push replacement. Here are the objective rules that cut through it.
Multiply the repair quote by the system’s age. Under $5,000: repair. Over: replace. A $600 repair on an 8-year-old unit scores 4,800 — fix it. A $1,400 repair at 12 years scores 16,800 — that repair is a down payment on the next failure. It is a rule of thumb, not law, but it correctly prices the risk of stacking repairs on aging equipment.
Compressor or heat exchanger failure out of warranty (the two most expensive components — replacing them in an old chassis rarely makes sense). Systems using phased-out refrigerants where a leak repair means recharging with increasingly scarce, expensive gas. Repeated repairs: two service calls in one year on a 10+ year system is the pattern, not bad luck. And a cracked furnace heat exchanger is a carbon monoxide risk — replacement, full stop.
Central AC alone: $4,500–$9,000 installed. Furnace: $3,500–$7,500. Full system (AC + furnace or heat pump): $8,000–$16,000, more for high-efficiency or ductwork repairs (see our HVAC installation cost guide). Federal tax credits currently cover up to $2,000 on qualifying heat pumps — ask every bidder to quote a heat pump option alongside like-for-like.
Never decide from one opinion — diagnosis quality varies wildly. Get the failing part and diagnostic reading in writing, then post the job and collect 2–3 bids. Efficiency math matters too: replacing a 10 SEER dinosaur with a 16+ SEER2 system cuts cooling costs 30–40%, which shortens the real payback on replacement.
Post your project once — verified, insured local pros send you free competing quotes, and escrow protects every payment.
Get 3 Free QuotesRepair cost × system age. Under 5,000: repair. Over: replace. A $500 repair at 8 years old (4,000) is worth doing; the same repair at 14 years (7,000) is money into a dying system.