Questions to Ask Your HVAC Contractor
By Danish Javaid, founder & editor · Published
The most useful questions to ask an HVAC contractor concern the load calculation, equipment selection, airflow, installation scope, and startup verification. Ask for written evidence and defined deliverables. A reassuring sales answer or a calculator estimate cannot establish that the proposed system suits your home.
Why the questions matter
Replacing a furnace, air conditioner, or heat pump is one of the larger purchases in a home, yet quotes often arrive with little more than a brand, a tonnage, and a price. Equipment size should come from a calculation, not a rule of thumb. When size comes from square footage times a number, or from matching whatever was there before, the result can be too large, and an oversized system may short-cycle, remove moisture poorly, and cost more to buy and run. The questions below bring sizing and scope into the open so bids can be compared on substance rather than on the bottom line.
Ask for evidence you can keep
| Question | Useful answer or document | Reason to ask again |
|---|---|---|
| What are my heating and cooling loads? | Report with inputs, design weather, and sensible/latent cooling | Only a square-foot rule or old equipment label |
| Why these exact models? | Matched-system selection at local design conditions | Only nominal tonnage or an “up to” efficiency claim |
| Can my ducts carry the required airflow? | Inspection and measurements, with repair scope if needed | No return-path, pressure, or airflow evaluation |
| What happens on the coldest design day? | Heat pump output, backup heat, and control sequence | No low-temperature capacity data |
| What is included in the price? | Models, materials, permits as applicable, exclusions | Broad promises such as “complete installation” |
| How will you verify startup? | Manufacturer procedure and documented results | Only a claim that air will feel cold |
| Who handles warranty and corrections? | Parts/labor terms, registration, service responsibilities | Unwritten coverage or acceptance promises |
The questions in detail
1. Did you perform a Manual J load calculation, and can I see it?
Manual J is the ACCA method for calculating a home's heating and cooling loads from design temperatures, insulation, windows, air leakage, orientation, and internal gains, which a square-footage rule ignores. A real calculation produces a report with a heating load, a cooling load split into sensible and latent parts, and the inputs behind them. Ask to see it. “I've done this for years” is not a calculation. You can explore your own assumptions first with the Manual J calculator so you know the rough neighborhood, remembering that it is an estimate, not a permit-ready report.
2. How did you choose this equipment?
Manual J gives the load; Manual S selects equipment that matches it. Ask how each model was chosen and how its capacity at your design conditions compares with the calculated load. “We always install four tons for a house this size” is not an answer. A better answer states the calculated load, the selected model's total, sensible, and latent capacity at your design conditions, and the percentage of the load that capacity represents.
3. What efficiency are you proposing, and why?
Request the exact matched-system SEER2 and EER2 ratings, and HSPF2 for heat pumps. Higher ratings usually cost more up front and lower operating cost, but how much depends on climate, energy prices, and runtime. Ask for the quoted upgrade premium and the assumptions behind projected savings, and be as skeptical of a top tier chosen with no reasoning as of the cheapest builder-grade unit chosen only for price.
4. Did you evaluate the existing ductwork?
New equipment connected to undersized or leaky ducts can underperform regardless of its rating. A thorough contractor checks the airflow the new equipment requires, measures static pressure at the manufacturer's boundary, inspects returns, and looks for leakage. If ducts need work, that belongs in the quote as a line item, not as a comfort complaint after installation. The static pressure and duct sizing articles explain what to expect.
5. Are you licensed, insured, and pulling a permit?
Ask what licenses and insurance are required locally, and verify them yourself through the licensing authority. A permit puts a third-party inspection behind the work, and in some jurisdictions a load calculation is part of that review. A contractor who proposes skipping the permit to save time is skipping the oversight that protects you, and the omission can cause trouble at resale or in an insurance claim.
6. What is included, and what is warrantied?
Get the scope in writing: model numbers, line sets, electrical work, duct modifications, thermostat, startup commissioning, haul-away, and cleanup. Separate the manufacturer's parts warranty, which may require registration by a deadline, from the contractor's labor warranty on the installation. A vague quote is where change orders and uncovered repairs tend to hide.
Sizing: ask what the numbers mean
Manual J calculates the load; Manual S selects equipment; Manual D supports residential duct design. Ask which parts are included. Cooling total should be separated into sensible and latent loads. For furnaces, compare output with heating load rather than comparing fuel-input BTU/h directly.
Commonly cited Manual S limits are roughly 95–115% of total cooling load, with heat pumps up to about 125% in heating-dominated climates, and furnace output about 100–140% of heating load. Sensible and latent capacities must cover their respective loads. These are screening limits, not universal permission to round up: use the applicable Manual S edition, equipment type, manufacturer performance data, and local requirements.
Ask whether design capacities come from expanded manufacturer data and whether minimum capacity suits mild-weather loads. A nominal 3-ton system is not guaranteed to deliver exactly 36,000 BTU/h under your conditions. A larger nameplate is not automatically an upsell; request the selection justification before judging it.
Airflow and commissioning
Ask what airflow the equipment requires and how it will be measured. About 400 CFM per ton is a rough assumption, not a universal setting. Static pressure must use the manufacturer’s measurement boundary and blower data. Request checks of room delivery, closed-door return paths, refrigerant charge under the specified procedure, condensate drainage, controls, and heating safety checks as applicable.
Scope, authorization, and warranty
- Who obtains any required permit and inspection, and who resolves review comments?
- What licenses and insurance are required locally, and can you independently verify them?
- Which ducts, line sets, electrical circuits, fuel connections, drains, and controls are reused or changed?
- What can trigger a change order, and must you approve the price before the work?
- What are the parts and labor warranties, registration deadlines, exclusions, and service-call responsibilities?
Do not assume every parts warranty lasts a particular number of years or that a permit guarantees every aspect of performance. Obtain the actual terms and a defined commissioning record. For newer refrigerants such as R-454B or R-32, ask about the specific manufacturer installation requirements rather than assuming existing components can be reused.
Efficiency and incentives
Request the exact matched-system SEER2/EER2 and heat-pump HSPF2 ratings. These rating systems took effect January 1, 2023. Ask for the quoted upgrade premium and the assumptions behind projected savings. Federal §25C is unavailable for equipment placed in service in 2026; confirm any state or utility rebate directly before treating it as a discount.
Good answers and red flags
| Topic | What a good answer sounds like | Reason for concern |
|---|---|---|
| Load calculation | Here is the report with its inputs | Square-footage rule of thumb |
| Load numbers | Heating, sensible, latent, and total cooling shown | Cannot or will not share them |
| Equipment size | Load, selected capacity at design conditions, and percentage | “We always install this size” |
| Efficiency | Justified against your climate, rates, and usage | Top tier with no reasoning |
| Ductwork | Airflow and static pressure measured, repairs priced | Old ducts reused without evaluation |
| Licensing and permit | Verifiable license, insurance, permit pulled | Suggests skipping the permit |
| Warranty | Written parts and labor terms | Verbal promises only |
Use the answers to compare proposals
Get several written quotes and ask each contractor the same questions. Resolve different load inputs or installation scopes before comparing totals. If one report uses different glazing, leakage, ventilation, or design weather, ask why. Contractors who size from a documented calculation should be able to explain any difference in their results; a bid far above or below the others deserves a specific explanation. An estimate from the HVAC load calculator is useful for reviewing assumptions, but disagreement with it does not prove a contractor’s report is wrong. Choose a documented design and accountable installation process, not a bidder solely because the tonnage or price is lower.
When quotes are in hand, the next step is the quote verification checklist, and the guide to reading a Manual J report helps with the load documents themselves.
Continue with: Verify a quote; Read the load report; Current incentives.
References and verification
ACCA Manual J; ACCA Manual S; ACCA Manual D; IRS: home energy credit expirations.
Calculation guidance is reviewed against our published methodology. To report an error or request a correction, use the contact page.