Before you replace your HVAC: the 12-point checklist

Age sets the whole conversation. Central AC and heat pumps hit diminishing returns around 10–15 years; gas furnaces last 15–20 years if the heat exchanger is intact. A 9-year-old unit with one bad part is usually a repair; a 16-year-old one that needs a major component is usually a replace. You don't have to guess the age. It's encoded in the unit.

Two rules of thumb, used as a trigger to investigate, not a verdict:

• The "$5,000 rule": age (years) × repair cost ($). Over $5,000 leans replace. (A 12-year AC × a $500 repair = $6,000 → lean replace.) Many sources now call $5,000 outdated given higher equipment costs and the refrigerant phase-out, and suggest $6,000–$7,000, so treat it as a flag, not a line.
• The 50% rule: if a repair is ≥50% of a new system's price, especially past mid-life, replacement usually wins.

Not every failure means a new system. Rough installed ranges so you can sanity-check a repair quote:

• Capacitor ~$150–$400 (the most common, cheapest fix)
• Blower motor ~$300–$900 (up to ~$2,000 for a variable-speed/ECM motor)
• Refrigerant recharge ~$250–$700, but rising fast as R-410A is phased down (see #8)
• Evaporator / condenser coil ~$1,900–$3,000, often a tipping point
• Compressor ~$1,200–$2,500: the priciest; frequently tips toward replace
• Heat exchanger (furnace) ~$1,250–$3,000: safety-critical (carbon monoxide); on an old furnace this usually signals replacement

This is the single most important thing you can insist on. A Manual J load calculation sizes the system to your house (its insulation, windows, orientation, air-tightness, and local climate) in BTU/hr. "Replace what you had" or "one ton per 500 square feet" just repeats whatever mistake was baked in years ago, and ignores any insulation or windows you've added since.

Most homeowners assume a bigger system is safer. The opposite is usually true. The U.S. Department of Energy estimates a large share of residential systems are oversized, and an oversized system short-cycles: it blasts to temperature and shuts off before it removes humidity, leaving you "cold but clammy," with uneven rooms and a compressor that wears out faster. Sizing rules cap oversizing tightly (generally no more than ~15% over the calculated load for a standard AC) for exactly this reason.

Before you spend five figures on equipment, ask whether some of that comfort problem is the house, not the machine. Air-sealing and insulation often deliver more comfort per dollar than a higher efficiency number: the EPA/Energy Star estimate ~15% average savings on heating and cooling from air-sealing plus insulation, and because they reduce the load, they can let you buy a smaller, cheaper system.

A heat pump or electric backup is a big new electrical load (~30–60 A). An older 100A panel that's already near capacity may need an upgrade to 200A or a dedicated circuit, often $1,500–$4,000 (more in high-cost areas, sometimes $5,000–$7,000+ with a new meter base or code work). It's usually not in the equipment quote.

The most fact-sensitive item on the list. As of Jan 1, 2025, new residential AC and heat pump equipment can no longer be made or imported with R-410A; new systems use R-454B or R-32 (both mildly-flammable "A2L" refrigerants). Two things follow:

• New systems cost a bit more: the A2L equipment premium runs roughly +8–15% (extra sensors, sealed relays, leak detection, new tooling passed through).
• Keeping an old R-410A unit gets pricier: R-410A is getting scarce, so recharges are climbing. A leaky system can rack up $2,000–$3,500 in refrigerant over five years, which often tips the scale toward replacing. You also can't mix refrigerants, so a new A2L system needs matched indoor + outdoor units (you generally can't keep an old R-410A coil and bolt on a new condenser).

Two physical items that often surface mid-job:

• Gas line / meter sizing. Your gas pipe and meter were sized for the original appliances. A bigger furnace or a tankless water heater can exceed capacity, requiring a larger line (~$500–$1,500) and sometimes a utility meter upsize. Applies to furnace upsizes and tank-to-tankless swaps.
• Line-set reuse. The copper refrigerant lines between indoor and outdoor units often shouldn't be reused with new refrigerants. Old oil/residue doesn't mix with the new synthetic oils, and diameters may differ. Replacement runs ~$500–$1,200. Cautious installers just run new line sets.

A perfect unit on bad ducts still underperforms. The DOE estimates duct leaks can waste 20–30% of cooling energy. New equipment may also need duct or return modifications (a return drop ~$300–$400; per-run work $300–$1,200). And a few things only bite in certain homes:

• Permits & inspection: required in most areas even for a like-for-like swap. The cash "no-permit deal" can void insurance, complicate a sale, and trigger fines + retroactive permits later.
• Asbestos: pre-1980 homes may have asbestos duct wrap or insulation that needs licensed abatement before tear-out ($2,000–$3,500+). Don't let a crew rip out suspect wrap dry.
• Condensate drainage & access: a new high-efficiency furnace produces water that needs a drain or pump; bigger equipment may not fit the old closet/attic access. Plus a C-wire may be needed for a smart thermostat in an older home.

A higher SEER2 number saves some energy, but the dollar payback on the efficiency premium alone is often long, in moderate and cold climates, going from ~14 to ~18 SEER2 can save only ~$65–$130/yr in cooling, a payback that can outlast the equipment. Cooling efficiency pays back fast mainly in hot climates; heat-pump efficiency pays back big mainly when you're replacing propane, oil, or electric resistance heat, not cheap natural gas.

Be careful with rebate promises. The federal 25C tax credit is dead for systems placed in service after Dec 31, 2025: do not let anyone bake a 2026 federal credit into your numbers. What survives is income-gated and state-run: the IRA HEAR/HOMES rebates (heat pump up to ~$8,000, panel up to ~$4,000, ~$14,000 household max) cover up to 100% of cost at ≤80% of area median income, 50% at 80–150%, and generally nothing above 150%. They're first-come and unevenly available by state.