Quick answer
Replacing the AC alone makes sense when your furnace is young and sound — match the new condenser's SEER2 tier to your budget and move on. But if the furnace is also past 12–15 years, a cold-climate heat pump usually wins: it replaces both boxes with one system, and it's the only path Washington's rebate programs actually fund. The worst time to decide is mid-heat-wave, so run this comparison before July.
- Furnace under ~10 years old: replace the AC like-for-like ($9,000–$15,000 installed for a quality central system in the Puget Sound).
- Furnace also aging: price the heat pump crossover ($12,000–$20,000 before rebates) — one system replaces both, and WA HEAR can take up to $8,000 off for income-eligible households.
- SEER2 tiers are a comfort decision as much as an efficiency one — variable-speed equipment cools more evenly and quietly.
- Cooling-only AC earns almost no rebate support in Washington; heat pumps earn the most.
Use this guide when
Your AC died during a heat wave and you're choosing like-for-like vs upgrade under pressure, your system is limping past 12–15 years and you want to decide calmly, or you're already planning a furnace replacement and wondering whether to fold cooling into the same project.
What actually drives the decision
Two things dominate: the age of your furnace (because the AC and furnace share the blower and ductwork, their replacement timing is linked) and rebate eligibility (because Washington's programs fund heat pumps, not cooling-only equipment). Everything else — SEER2 tier, brand, single-stage vs variable-speed — is tuning within whichever path you pick.
Compare your options
Like-for-like AC replacement
Right when your furnace is young and sound. You're buying a new outdoor condenser and coil matched to the existing blower — typically $9,000–$15,000 installed in the Puget Sound depending on tonnage and efficiency tier. Base-tier SEER2 equipment satisfies code; higher tiers buy quieter, more even cooling and lower summer bills.
Heat pump crossover
Right when both boxes are aging. A cold-climate heat pump replaces the AC and the furnace's job in one system ($12,000–$20,000 before incentives), heats at 2–4× the effective efficiency of gas in our climate, and unlocks the rebate stack: WA HEAR up to $8,000 (income-eligible), PSE rebates of $500–$1,500, and Seattle City Light instant discounts for its customers.
Repair one more season
If the failure is a capacitor, contactor, or fan motor on a system under 12 years, a few hundred dollars buys you time to plan. Use it: get the comparison quotes now so next summer's decision is a phone call, not a scramble.
Key terms and context
This guide is written for heating & air decisions in the Puget Sound. It uses the same terminology you'll hear from inspectors, technicians, and permit offices.
Mismatching new AC with an old furnace
A new high-SEER2 condenser paired with a 20-year-old furnace's blower may never deliver its rated efficiency or airflow — and when that furnace dies two winters later, you'll pay labor twice on the same ductwork. If the furnace is past 12 years, price the combined replacement before buying cooling alone.
Heat-wave panic buying
When the AC dies at 95°F, everything says 'fastest install wins.' That's how homes end up with oversized builder-grade equipment that short-cycles for 15 years. Oversizing is the classic rush mistake — a load calculation takes a day and protects a five-figure purchase.
How we build this guidance
- We quote the AC-only and heat-pump paths side by side with rebate math included — the honest comparison is net price, not sticker.
- Every system is sized by load calculation, not by matching the old unit's tonnage.
- Spring scheduling beats July emergencies — we'll tell you if your system is worth nursing one more season.
Methodology: Equipment tiers and install ranges from Eco's published Puget Sound cost guide; sizing per ACCA Manual J; 2026 rebate rules (WA HEAR, PSE, Seattle City Light) verified at estimate.
Last updated: 2026-07-05
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Common questions
When is the best time to replace an AC in the Puget Sound?
Spring, before the cooling season. Scheduling is open, you have time for a proper load calculation and rebate check, and you're choosing equipment instead of taking whatever's on the truck. July failures during a heat wave are the most expensive way to buy the same system.
What SEER2 rating do I actually need?
Code sets the floor, and in our short cooling season the pure-payback case for premium SEER2 tiers is weaker than in Arizona. What the higher tiers reliably buy here is comfort: variable-speed systems run longer and gentler, hold temperature evenly, dehumidify better, and are dramatically quieter. Buy tier for comfort first, efficiency second.
My AC died but my furnace is fine — should I still consider a heat pump?
Ask how old the furnace is. Under about 10 years: replace the AC and keep the furnace. Past 12–15: a heat pump replaces the dying AC now and takes over heating too, capturing rebates cooling-only equipment can't. Some homes split the difference with a dual-fuel setup — heat pump primary, existing furnace as backup.
How long does an AC replacement take?
Most straight condenser-and-coil replacements are one day. Add time when ductwork needs sealing or resizing, when electrical work rides along, or when a heat pump conversion adds a new indoor air handler. Permits and inspection are part of every legitimate Puget Sound install — we handle both.