Blog · August 18, 2026
10 Questions to Ask an HVAC Contractor Before You Sign Anything
Replacing a furnace and air conditioner is one of the biggest purchases most homeowners never plan for. It usually starts with a system that quit in the first hot week of summer, three contractors through the house in two days, and three prices that are wildly far apart.
The spread is real, but it usually isn’t because one contractor is gouging you. It’s because the three quotes are for three different jobs — different equipment, different efficiency tiers, different assumptions about your ductwork. The questions below are how you force them onto the same page before you sign.
First, know what the number should look like
Per Sesklo’s HVAC cost guide, HVAC work across the 50 largest U.S. metros spans roughly $3,500 to more than $21,000 — the low end being smaller jobs and straight equipment swaps, the high end being full replacements with ductwork and electrical involved.
Location matters more than most people expect. The same full replacement has a typical cost about 54% higher in the priciest metros than the cheapest: a median near $7,000 in Oklahoma City versus roughly $10,800 in the San Francisco Bay Area. That’s not a materials difference — a condenser costs about the same anywhere. It’s local labor rates, permit regimes, and how competitive the market is.
Treat that as a sanity band, not a target. If a quote lands far outside the range for your metro in either direction, that’s your cue to ask why — and a bid that’s dramatically low is worth more scrutiny than a high one.
1. Did you run a Manual J load calculation, and can I see it?
This is the single most useful question on the list. Manual J is the industry standard method for sizing a system to your actual house — square footage, insulation, window area and orientation, air sealing, and local climate. It’s a calculation, not a guess.
Plenty of contractors skip it and just match whatever tonnage is on the old unit. That perpetuates whatever mistake was made 15 years ago. An oversized AC short-cycles: it cools fast, shuts off before it has pulled moisture out of the air, and leaves you with a house that’s cold and clammy. An undersized one never catches up in August.
Ask for the calculation in writing. A contractor who runs one will hand it over happily.
2. Is this a straight swap, or does my ductwork need work?
Ductwork is the line item that turns a predictable job into an expensive one. If your ducts are undersized, leaky, poorly routed, or missing in part of the house, the best equipment in the world will underperform — and fixing them can add thousands.
The important part is that this gets decided before you sign, not discovered mid-install. Ask specifically: did you inspect the ducts, what condition are they in, and is any duct work included in this price? If the answer is “we’ll see once we’re in there,” get that scoped and priced as a named contingency rather than an open-ended one.
3. What exact equipment am I getting?
You want three things in writing: manufacturer and model number for both the indoor and outdoor units, the capacity in tons, and the efficiency rating (SEER2 for cooling, AFUE for a gas furnace, HSPF2 for a heat pump).
Without model numbers you cannot compare two quotes at all. Efficiency tier alone can move the equipment cost substantially — the same manufacturer’s line typically spans a wide price range from base-tier to high-efficiency units. A quote reading “new 3-ton system — $9,400” tells you nothing about whether you’re getting the bottom of the catalog or the top.
4. Are the indoor and outdoor units a matched set?
Mixing a new outdoor condenser with an old or mismatched indoor coil is a well-known way to get a system that never hits its rated efficiency and may not be covered under warranty. If a quote is noticeably cheaper than the others, check whether it’s reusing the existing air handler or coil.
Sometimes reusing is a legitimate, deliberate choice — a coil that’s five years old and sized correctly, for instance. It just has to be a decision you made on purpose, with the tradeoff explained.
5. Does the price include the permit and the inspection?
Most jurisdictions require a permit for HVAC replacement, and the inspection that follows is how the work gets verified against code. The permit fee itself is usually minor. Its absence is not — unpermitted mechanical work has a habit of surfacing at resale, and it means nobody independent ever looked at the install.
Ask whether the permit is pulled by the contractor, included in the price, and who meets the inspector. If a bid is cheaper because it skips the permit, it isn’t cheaper.
6. What’s included if you find something behind the old unit?
Replacements routinely turn up adjacent problems: a disconnect or breaker that doesn’t meet the new unit’s requirements, a refrigerant line set that needs replacing for a modern refrigerant, a condensate drain with nowhere good to go, a gas line that’s undersized, or a rusted-out plenum.
Ask what’s included, what’s excluded, and what the contractor charges if each of those shows up. Electrical is the most common one — if your panel is older or already full, a new circuit may need electrical work that isn’t in the HVAC quote at all. Better to price that now than to find out on install day.
7. Who is actually doing the install?
Equipment quality matters less than installation quality. A mid-tier system installed well will outperform a premium system installed badly, every time.
So ask who’s coming: the contractor’s own crew, or a subcontractor? How long have they been doing this? Is anyone on the crew certified for the refrigerant handling and startup procedure the manufacturer requires? And will someone commission the system at the end — check the refrigerant charge, verify airflow, confirm the thermostat is configured for your equipment — rather than just turning it on and leaving?
8. What rebates or tax credits does this equipment qualify for?
High-efficiency equipment often qualifies for utility rebates, state programs, or federal tax credits, and these can be worth real money. They also change frequently, vary by state and utility, and depend on the specific model’s ratings.
Don’t accept a vague “you’ll get money back.” Ask the contractor to name the specific program, state the amount, confirm the exact model qualifies, and say clearly who files the paperwork — many utility rebates have to be submitted by the installing contractor within a set window after the job. Then verify it yourself with your utility. A contractor’s rebate estimate is a sales aid, not a guarantee.
9. What are the warranties — both of them?
There are two, and they’re separate.
The manufacturer warranty covers the parts. It’s typically the longer of the two, and many manufacturers require you to register the equipment within a short window after installation to get the full term rather than a shorter default. Ask who registers it — the contractor usually can, but only if they actually do.
The labor warranty is the contractor’s own, and it’s the one that varies most between bids. It covers the cost of the technician who comes out to install a part the manufacturer will happily send you for free. One year is common; longer terms exist. When two quotes are close, the labor warranty is often the real difference.
Ask both, in writing, and ask what voids each one.
10. What does maintenance look like after the install?
Most manufacturer warranties expect documented annual service, and skipping it can complicate a claim later. Beyond the paperwork, an annual check is genuinely how a system gets to the top of its expected lifespan instead of the bottom.
Ask whether the contractor offers a recurring maintenance plan, what a visit actually includes, and whether plan customers get priority scheduling in July when everyone’s system fails at once. Get the visit checklist, not just the price — “annual tune-up” covers everything from a thorough inspection to a filter change and a handshake.
The short version of the red flags
If you only remember a handful of things: be wary of a quote with no model numbers, no permit line, no load calculation, and a discount that expires today. High-pressure same-day pricing on a five-figure mechanical system is a sales tactic, not a deal — a legitimate contractor’s price will still be there tomorrow.
And get three quotes. Not because the cheapest wins, but because the second and third quotes are what teach you which questions the first one didn’t answer.
Ready to compare HVAC quotes side by side? Describe your project once on Sesklo — add photos or a short video of your existing system, the label on the outdoor unit, and where it’s installed — and get structured quotes from local contractors laid out in the same format, so you’re comparing the same job instead of decoding three different PDFs. Get started here.