A new heating-and-cooling system is one of the biggest unplanned purchases most homeowners ever make, usually decided under pressure, with one quote on the table. This is the single page you take to the kitchen table. Ask these ten and a fair quote survives them; a sales pitch doesn't.
The questions cluster into three jobs. Questions 1–2 make sure you're buying the right size system for your house, not a copy of the old one. Questions 3–7 drag the hidden line items into the light before they show up as a change order. Questions 8–10 keep the repair option and the real numbers on the table. Get the answers in writing, not as promises.
Ask them in order. Write the answers on the quote itself.
A Manual J sizes the system to your house (insulation, windows, orientation, air-tightness, climate) in BTU/hr. "We'll just match your current unit" repeats whatever mistake was baked in years ago and ignores any insulation or windows you've added since. A good contractor does this as a matter of course.
Flag: "Same size as what you had" instead of a calculation. That's how oversized systems get sold.
Bigger isn't safer. An oversized system short-cycles: it blasts to temperature and shuts off before it removes humidity: "cold but clammy," uneven rooms, faster wear. Sizing rules cap oversizing at roughly 15% over the calculated load for exactly this reason. If you've air-sealed or added insulation, the right new size may be smaller, and cheaper.
Flag: Anyone upsizing you "to be safe." Don't let them.
A heat pump or electric backup is a big new load (~30–60 A). An older 100A panel near capacity may need a 200A upgrade or a dedicated circuit, often $1,500–$4,000, and it's usually not in the equipment price. Most at risk: pre-2000 homes, all-electric conversions, and homes already loaded with EV chargers or electric ranges.
Flag, both ways: a surprise panel charge after you sign, or a blanket "every heat pump needs a new panel" (it depends on your existing load).
As of Jan 1, 2025, new residential equipment can no longer be made with R-410A; new systems use R-454B or R-32 (mildly-flammable "A2L" refrigerants). That carries a roughly +8–15% equipment premium. You can't mix refrigerants, so a new A2L system needs matched indoor and outdoor units. You generally can't keep an old R-410A coil and bolt on a new condenser. Rules vary by state; some are stricter (New York's R-410A ban hit Jan 1, 2026).
Flag: a quote that pairs a new condenser with your old coil. Confirm your state's rules.
The copper refrigerant lines between the indoor and outdoor units often shouldn't be reused with new refrigerants. Old oil and residue don't mix with new synthetic oils, and diameters can differ. New line sets run ~$500–$1,200. Cautious installers just run new. Either answer can be fine. You just want it decided, and priced, up front.
Flag: the line set surfacing as a change order after work starts.
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. It applies mainly to furnace upsizes and tank-to-tankless swaps. Ask before you commit, not after.
A perfect unit on bad ducts still underperforms; duct leaks can waste 20–30% of cooling energy, and new equipment may need return or duct modifications. And permits are 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 later. In pre-1980 homes, also ask about asbestos duct wrap (licensed abatement, $2,000–$3,500+).
Flag: a quote that skips the duct inspection, or a "we don't need a permit for this" pitch.
The repair option must always be on the table. A capacitor (~$150–$400) on a 9-year-old unit is a repair, not a reason to replace. A contractor who jumps straight to "new system" without pricing the repair is selling, not diagnosing. Get both numbers in writing and compare cost-per-remaining-year: the repair divided by realistic years left, versus a new system divided by its lifespan.
Flag: "It's not worth repairing" with no repair number to back it up.
A higher SEER2 number saves some energy, but in moderate and cold climates the dollar payback on the efficiency premium alone is often longer than the equipment lasts. The real reasons to pay up are comfort, humidity control, quiet, and longevity, not an inflated utility-bill promise. 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.
Flag: a pitch that leads with huge bill savings. Make them show the numbers for your ZIP.
The federal 25C tax credit is dead for systems placed in service after Dec 31, 2025. Don't let anyone bake a 2026 federal credit into your numbers. What survives is income-gated, state-run IRA HEAR/HOMES rebates plus utility programs. Check DSIRE (dsireusa.org), the ENERGY STAR Rebate Finder, and your local utility for your ZIP. And watch financing: most "0% APR" offers are deferred interest. One dollar left at the promo's end can trigger all the back-interest at once.
Flag: a 2026 federal tax credit on the quote, or a "0%" offer you can't get the fine print on.
The ten questions plus the red flags to watch for, so you can take it to every quote. One email, no spam.