HVAC Replacement Estimate: The 14 Lines It Must Show

Three bids for the same HVAC replacement — furnace and coil, one house, one week — sat on my kitchen table last spring, and the highest was well over half again the lowest. I am deliberately not printing the three numbers, because a price from another market, another house and another year is the least useful thing I could hand you. The spread was nearly useless to me as well, for a better reason: the three sheets were not describing the same job.

Some states legislate against exactly that gap. California requires a home improvement contract to carry the heading "Description of the Project and Description of the Significant Materials to be Used and Equipment to be Installed", followed by a description of both — Business and Professions Code §7159(d)(7). Treat that heading as the bar a bid clears before its total is worth comparing to anything, wherever you happen to live.

The cheapest was four lines long. An outdoor unit model number, "new coil," "new pad," a total. The most expensive named nine separate components and volunteered an AHRI reference number I hadn't asked for. The middle one felt substantial — two pages, a logo, a payment schedule — and it was the one I nearly signed. Then I laid the three side by side and started ticking off what each one actually promised. The middle bid never said whether the line set was being replaced. It never said who was pulling the permit. It never named the indoor coil.

I signed nothing that week. Here is the checklist I built out of that afternoon, and have used on every bid since, including on a rental unit where I got it wrong once and paid for it.

How to use this

Print the bids. Not on screen — on paper, side by side, with a pen. Work down the 14 lines below and write the line number in the margin wherever you find it. At the end you will have three sheets with different numbers written on them, and the gaps will be obvious in a way they never are on a phone. If you want the arithmetic afterwards, the bid comparison calculator adds the missing items back before it ranks anything.

I am not a licensed contractor and I inspect nothing. What follows is document comparison: what the bid claims, and which document you can open to check the claim. Where a code section is cited, I read it on 17 August 2026 and noted the edition, because codes get amended and an undated citation becomes a wrong one.

The lines I am not counting

Price, deposit, payment schedule, the change-order clause and the cancellation notice are on almost every bid, and nobody forgets to read them. They are also frequently required by state law rather than by good practice — California's Business and Professions Code §7159 and New York's General Business Law §771 both list required contents for a home improvement contract in writing. California also caps the down payment at $1,000 or 10 percent of the contract price, whichever is less — §7159(d)(8) puts that sentence on the contract in 12-point bold, and CSLB says flatly there are no exceptions for special-order materials. New York's §771 requires a notice that the owner may cancel until midnight of the third business day after signing. Those deserve their own treatment. The 14 below are the ones that go missing.

Lines 1–3: who is doing the work, and what work

Line 1 — Legal business name, business address, and licence number. Not a logo and a mobile number. The licence number is what lets you open your state's licensing database and confirm the entity on the paper is the entity that holds the licence, and that the classification covers mechanical work. In California this is statutory: B&P §7159(d)(1) requires "the name, business address, and license number of the contractor" in the contract itself, and CSLB repeats it in plain language for consumers. Missing: you cannot look anyone up, and if the crew that shows up works for a different entity than the one on the contract, you find out during a dispute rather than before one.

Line 2 — An approximate start date and an approximate substantial completion date. NY GBL §771(b) goes further and asks whether the parties have agreed that a definite completion date is of the essence. Missing: "we'll get to you" is not a schedule, and with no dates you have nothing to point at when the equipment sits in your garage for five weeks.

Line 3 — The scope in physical terms: what comes out, what goes in, what stays. Old equipment removal and disposal. New pad or new stand. Whether the existing thermostat stays. Whether ductwork, plenums, and the filter cabinet are touched at all. Missing: every ambiguity gets resolved in the contractor's favour on the day, and "I assumed the old furnace haul-away was included" is not a position you can defend.

Lines 4–7: the equipment, by model number

Line 4 — Every model number. Outdoor unit, indoor coil or air handler, and the furnace if one is involved. A split system is a pair. Half a pair on paper is not a specification. Missing: the installer can put any coil on that condenser and the bid is still technically satisfied.

Line 5 — The AHRI Certified Reference Number for that exact combination. This is the one line that turns the whole equipment section from a claim into something you can check yourself, at ahridirectory.org. The directory's residential search asks for brand and model of the outdoor unit and of the indoor unit; it does not ask for serial numbers, which is worth knowing because nothing needs to be installed yet for you to run the check. The reference number identifies a matched system — that pair, rated together. Missing: the SEER2 figure on the bid is coming from a brochure for the condenser, and a condenser paired with an undersized or unmatched coil does not deliver the brochure rating. Ask for the number in writing. How long it takes to arrive tells you something on its own.

The number can also be checked at the far end without anyone's permission. The directory's public search takes either a reference number or a model number, and AHRI's own login notice says accounts are not issued to people who want to search products or download certificates, "as this can be done on the public site without logging in." A certificate that arrives as a PDF goes back through the Verify Certificate page, which asks for the reference number, the date as it appears on the certificate, and the certificate number printed in the bottom right corner — certificates printed from the directory after 30 July 2009 are covered.

Line 6 — The certified capacity and efficiency of the combination. Nominal cooling BTU/h, SEER2, EER2, and HSPF2 for a heat pump; AFUE and input BTU/h for a furnace. Certified values, from the directory entry, not from the sales sheet. Missing: you cannot compare bids on efficiency at all, and you cannot check the system against the DOE regional minimum that applies where you live. Since 1 January 2023 those minimums are regional and written into 10 CFR 430.32(c): a split-system air conditioner under 45,000 BTU/h has to hit 13.4 SEER2 nationally but 14.3 SEER2 if it is installed in the Southeast or Southwest region, and the Southwest adds an EER2 floor on top. That is why a friend two states away gets quoted a differently rated unit for what sounds like the same house.

Line 7 — The refrigerant, and the equipment's date of manufacture. R-410A or R-454B changes the answer to "what happens in year eight." The date of manufacture changes whether the unit is even legal inventory. Under the AIM Act's Technology Transitions programme, new residential split systems moved to lower-GWP refrigerants for 2025 manufacture; EPA's final rule of 26 May 2026 (FR doc. 2026-10387, effective 27 July 2026) then removed the 1 January 2026 cut-off that would have banned installing pre-2025 R-410A stock, which NAHB summarises as installation permitted until existing supplies run out. Some states kept the earlier deadline in their own law — NAHB names New York, where the 1 January 2026 date was codified statewide. Start at EPA's Technology Transitions page and then check your state, because this is the one line on the bid where the federal answer and your state's answer can differ outright. Missing: you may be buying old stock at new-stock prices without being told it is old stock — which can be a perfectly good deal, but only if you know.

Lines 8–12: the installation, where the money actually hides

Line 8 — The load calculation the tonnage came from. IRC section M1401.3 (2021 edition, read 17 August 2026) states that equipment "shall be sized in accordance with ACCA Manual S or other approved sizing methodologies based on building loads calculated in accordance with ACCA Manual J or other approved heating and cooling calculation methodologies." Two documents, in that order: Manual J produces the load, Manual S selects the equipment against it. Manual D covers duct design, and matters the moment anyone touches a duct. Missing: the size came from the label on the old unit, or from square footage divided by a rule of thumb. If the bid says "load calculation performed" with no attachment, ask for the report. A real one names your window areas and orientations. Note that adoption varies — confirm which IRC edition your jurisdiction adopted and how it amended this section.

Line 9 — The line set: replaced or reused, with length and diameter. Manufacturers ship condensers with a factory charge covering a stated tubing length (15 feet is a common figure) and their installation instructions give a charge adjustment per additional foot. If the existing line set is being reused, the bid should say so, and say what happens about flushing it and about the fittings. Missing: this is the classic mid-job change order. You agreed to a total that quietly assumed a reuse, and on install day the reuse turns out to be impossible. A per-foot price for line set, agreed before signing, is the cheapest half-hour of the whole project — the change-order clause that reopens a fixed price covers what that sentence has to say.

The refrigerant decides part of this, so put the two questions in one sentence. Where the new system uses an A2L such as R-454B, whether the existing tubing can be reused is answered by that system's installation instructions rather than by what is already in the wall, and whether the equipment can be installed at all depends on what your jurisdiction has adopted — AHRI publishes a state-by-state map of where "state and local building codes have been updated or legislation passed to allow equipment using A2L refrigerants," and says it revises the map as those codes change. Reuse or replace, length in feet, both tube diameters: three entries on the bid, and the install-day version of the conversation stops being available.

Line 10 — Condensate: primary drain, trap, and secondary protection. IRC M1411.3.1 (2021 edition, read 17 August 2026) requires a secondary drain or auxiliary drain pan for each coil "where damage to any building components will occur as a result of overflow from the equipment drain pan or stoppage in the condensate drain piping," and gives compliance options including an auxiliary pan draining to a conspicuous point, or a pan with a UL 508 water level detection device that shuts the equipment off. Manufacturer instructions add their own requirements — a trap, and a positive slope on the drain line. Missing: if the air handler is in an attic above finished ceilings, this is the line that decides whether a clogged drain costs you a service call or a ceiling.

Line 11 — Electrical: disconnect, whip, and a circuit sized to the nameplate. The equipment nameplate carries a minimum circuit ampacity (MCA) and a maximum overcurrent protection (MOCP); those two numbers, not the installer's habit, size the conductors and the breaker. NEC 440.14 requires the disconnecting means to be located within sight from, and readily accessible from, the equipment — with the caveat that states adopt the NEC on their own cycle and amend it, so which edition your inspector holds is a question for the building department, not for me. Missing: the existing disconnect and breaker were sized for the old unit. If the new unit's MCA is higher, someone has to pay for that work, and if it is not on the bid, it is not in the price.

Line 12 — Venting, combustion air, and gas piping — or, on a heat pump, the backup heat. For a gas furnace: vent category and vent material, termination and clearances, and whether the gas line is adequate. IRC G2407 (2021 edition, read 17 August 2026) governs combustion, ventilation and dilution air; its standard method at G2407.5.1 sets the minimum required indoor volume at 50 cubic feet per 1,000 BTU/h of appliance input rating, which is the calculation that decides whether a furnace can stay in the closet it is in. For a heat pump: the size and staging of the auxiliary heat, and the circuit it needs. Missing: replacing an 80% furnace with a 95% one changes the venting entirely, and if you share a chimney with a water heater, the water heater's venting is now part of the job whether or not it is on the bid. This is safety territory, so the correct move is not to work it out yourself — it is to make the contractor put their answer in writing and let the inspector see it.

Lines 13–14: permit and warranty

Line 13 — The permit, the inspection, and who schedules them. CSLB's consumer guidance is blunt about wanting "written direction as to who will get the necessary permits." A system replacement is regulated work in most jurisdictions; the IRC's permit exemption list is short and does not read like it was written to cover swapping a furnace. Your building department's own page is the authority here, not a national article — including on what the permit costs, since a bid that says "permit included" and one that says "permit by owner" are not the same price. Missing: you inherit unpermitted work, and it surfaces at the least convenient possible moment, which is during a sale.

The timeline and the permit's scope are both published, which makes them questions for before you sign rather than after. Seattle's building department tells applicants to "plan for 9 weeks from the time you apply to the time we issue your permit," states that an issued permit "is valid for 18 months after the issue date," and notes that a mechanical permit does not cover gas lines or refrigeration, which are separate permits. Your city will have its own numbers, but the three questions do not change: how long to issue, how long the permit stays alive, and how many permits this one job actually needs.

Line 14 — Warranty, split three ways. The manufacturer's parts term. Who registers the equipment and by what deadline. The contractor's own labour warranty and its length. These are three different promises from two different parties, and "10 year warranty" on a bid tells you which of them? CSLB lists getting "any warranty offered by the contractor for labor and materials in writing" among the basics. Missing: the most common failure I have seen. Registration windows are typically measured in weeks from installation, and the unregistered parts term is shorter — often much shorter — than the number printed in the brochure. Miss the window and you have paid for coverage you no longer have, and there is no notification, because nobody is obliged to send you one.

The bid I accepted on the rental unit

On the rental unit I accepted a bid that named the outdoor unit, the coil, and the AHRI number — I thought I had been thorough — and said nothing about ductwork. The existing return was undersized for the new blower. That conversation happened with the old system already on the driveway, which is the worst possible negotiating position, and it cost me a number I still find annoying.

So now I add a fifteenth question that is not a line on anybody's bid: what does this bid assume about my house that it does not say out loud? Duct condition. Attic access. Whether the pad is level. Whether the electrical panel has space. Asking it before signing costs nothing. Asking it on install day costs whatever the contractor says it costs.

What this list cannot do

It cannot tell you whether the tonnage is right — that is what the Manual J report is for, and reading one is a separate job. It cannot tell you whether a price is fair; the only honest comparison is against your own second and third bids for the same specified scope, which is the entire reason for pinning the scope down first. And code adoption is local: every IRC section above is from the 2021 edition, and your jurisdiction may be on a different edition with its own amendments. Confirm at your building department before you treat any of it as the rule where you live.

What the list does do is turn "this one feels more professional" into a count. Three bids, fourteen lines. Write the numbers in the margin and see which sheet is actually describing the job.