How to Choose a Heating and Air Conditioning Contractor: 8 Checks Before You Sign

To choose a heating and air conditioning contractor in California, start with the state license. Look the company up on the Contractors State License Board (CSLB) site and confirm a current, active C-20 license, a bond on file and workers' compensation, which CSLB requires of every active C-20 contractor, with or without employees. Then compare at least three written bids for the same scope of work, and ask who pulls the permit and books the Title 24 duct test. Never pay a down payment above $1,000 or 10% of the contract price, whichever is less (CSLB).

• Before You Call: What to Have Ready
• 1. Look Up the License
• 2. Read the Bond and Workers' Comp Lines
• 3. Make Sure the Person Matches the License
• 4. Expect a Real Home Evaluation
• 5. Compare Three Written Bids for the Same Job
• 6. Ask Who Pulls the Permit and Books the Duct Test
• 7. Read the Contract Before You Sign
• 8. Call References and Listen for Repair Options
• Red Flags and What to Do If a Job Goes Wrong
• The Bottom Line
• Frequently Asked Questions

This guide is about choosing the right HVAC contractor, the company that does the work on a home system, whether it's a repair, a replacement or a new install. What the system itself should be is a separate decision, covered on our residential HVAC design and installation page and in how to choose an HVAC system. Brand choice has its own guide too: what to look for when choosing an HVAC brand.

Whether you're hiring for a repair or choosing the company that will install a new heating and cooling system, every check below is something you can verify yourself, mostly from public records, before anyone sets foot in your attic.

Key Takeaways

• A California HVAC contractor should hold a current C-20 (warm-air heating, ventilating and air-conditioning) license. Check it on the CSLB license lookup, not just on the business card.
• The license page also shows the contractor's bond and workers' compensation policy. CSLB warns that a bond "do[es] not assure the financial or professional integrity or competency of a contractor."
• CSLB advises getting at least three written bids for identical plans and scope, and to beware of any bid that is substantially lower than the others.
• Under Title 24, replacing an air handler, the outdoor unit of an AC or heat pump, a packaged unit or a coil triggers duct sealing and a leakage test verified by a third-party rater, with a few exceptions listed in check 6. Since January 1, 2026 California calls that rater an ECC-Rater (it used to be a HERS rater).
• A written contract is required on home improvement jobs over $500, the down payment can't exceed $1,000 or 10% of the price, whichever is less, and you can cancel in writing within three days of signing.

Before You Call: What to Have Ready

ENERGY STAR's first tip for hiring a heating and cooling contractor is to study up. Learn your state's license and insurance requirements. Then know the model of your current system, its maintenance history and which rooms are uncomfortable before you call (ENERGY STAR). A photo of each unit's data plate covers the model and serial numbers. A note of the rooms that run hot or cold tells a good contractor where to look first.

1. Look Up the License

A C-20 license is the CSLB classification that covers home heating and cooling work in California. CSLB defines a C-20 contractor as one who "fabricates, installs, maintains, services and repairs warm-air heating systems," air-conditioning systems, "and the ducts, registers, flues, humidity and thermostatic controls and air filters in connection with any of these systems" (CSLB, C-20 classification).

Contractors must print their license number on their business card and on every bid and contract, but CSLB is blunt that "seeing a license number doesn't necessarily mean the license is valid" (CSLB, finding the right contractor). Type the number into the CSLB license lookup yourself.

Here is what the record looks like, using Alpha Mechanical's own license, CSL# 967727, as read on CSLB's site on October 14, 2026 (CSLB license detail):

Source note: each line above was read from CSLB's public license detail page on October 14, 2026, which stamps its data "current as of 10/14/2026." The bond and policy numbers are left out.

Two more lines are easy to miss. CSLB's disclosure of complaints is limited by law, so a disclosable action appears only as a link on the record when one exists, and only construction-related civil judgments reported to CSLB are listed. The page also notes when a contractor carries a rare Blanket Performance and Payment Bond, which matters for the down payment rule in check 7.

2. Read the Bond and Workers' Comp Lines

A contractor license bond is a bond that every California licensed contractor must carry. CSLB cautions that bonds "do not assure the financial or professional integrity or competency of a contractor," and that the bond "is often not enough to cover multiple complaints made against it or your project if it's worth more than the value of the bond" (CSLB). Treat the bond as a minimum, not a guarantee.

Workers' compensation matters more than most homeowners think. In CSLB's words: "if a contractor has employees, they are required to carry workers' compensation insurance," and "if a worker is injured working on your property and the contractor doesn't have insurance, you could be financially liable to pay for injuries and rehabilitation" (CSLB). For heating and air conditioning contractors the rule is stricter: CSLB says every active C-20 contractor, "whether or not they have employees," must carry workers' compensation insurance or have a valid Certification of Self-Insurance on file (CSLB). HVAC work means ladders, roofs, attics and gas lines, so a current policy on the license page is worth the minute it takes to check. CSLB also suggests asking your own insurer whether the contractor's coverage is adequate.

3. Make Sure the Person Matches the License

CSLB suggests asking the person who comes to give you a bid to show their pocket license and a picture ID, and making sure they are the same person named on the license. Salespeople need their own registration: a Home Improvement Salesperson (HIS) is a salesperson registered with CSLB to sell home improvement work for a contractor, and you can ask to see that registration card too (CSLB). The same CSLB lookup checks HIS registrations.

For the technicians, one federal credential applies: EPA rules under Section 608 of the Clean Air Act require technicians who "maintain, service, repair, or dispose of equipment that could release ozone depleting refrigerants into the atmosphere" to be certified (EPA, Section 608 technician certification). Ask any technician who will work on the refrigerant circuit to show that certification; EPA notes that it does not issue the cards itself. Look for NATE-certified technicians as well: NATE is an industry certification (NATE), and it adds to the license check rather than replacing it.

4. Expect a Real Home Evaluation

A good bid starts with a look at the house, not a price over the phone. ENERGY STAR says the contractor "should spend significant time inspecting your current system and home." It also notes that "a bigger system isn't always better," and that sizing should account for the size of the house, its insulation and its windows. It adds that a good contractor will inspect the duct system for air leaks and insulation and "measure airflow to make sure it meets manufacturers specifications" (ENERGY STAR).

If the contractor never steps into the attic or checks the ducts, the bid is a guess. Ask what they looked at and what they measured.

5. Compare Three Written Bids for the Same Job

CSLB's advice is to "get at least three written bids on your project, and make sure you're comparing bids based on identical plans, specifications, and scope of work." It also warns: "Do not automatically accept the lowest bid. In fact, you should beware of any bid that is substantially lower than the others" (CSLB). ENERGY STAR adds that bids should be compared on cost, energy efficiency and warranties, because the lowest price "may not be the best deal if it's not the most efficient" (ENERGY STAR).

The phrase that does the work is "same scope." Three bids only compare when each one names the same things:

• The exact equipment, by brand and model number, for every piece being replaced.
• Whether the permit and the Title 24 duct test (check 6) are included.
• What happens to the ductwork: tested and sealed, repaired, or replaced.
• Removal and disposal of the old equipment.
• The labor warranty, in writing, separate from the manufacturer's parts warranty.

A bid that leaves out the permit and the duct test isn't a cheaper version of the same job. It's a smaller job, and the code requirement doesn't go away because the bid left it out. CSLB says a bid far below the others "probably indicates that the contractor made a mistake or is not including all the work quoted by their competitors" (CSLB).

6. Ask Who Pulls the Permit and Books the Duct Test

This is the question that separates contractors fastest. The California Energy Commission puts it plainly: "Properly permitted work will trigger any necessary HERS testing. A contractor should understand and be able to explain permitting requirements to the homeowner" (CEC, HERS program).

The name changed in 2026. Since January 1, 2026, the field verification and testing that used to run through the HERS program sits in the Energy Code Compliance (ECC) program. An ECC-Rater is the certified third-party tester who checks that installed work meets the Energy Code (CEC, Energy Code Compliance program). You may still hear it called a HERS test; the CEC lets rating companies keep "HERS" in their names.

What the test checks on a typical change-out is set by Title 24. Under the 2025 single-family compliance manual, when an air handler, the outdoor unit of a split air conditioner or heat pump, a complete packaged unit, or a coil is replaced, the ducts connected to it must be sealed by the installer and verified by an ECC-Rater (CEC, 2025 Single-Family Residential Compliance Manual, chapter 9):

Source: CEC 2025 Single-Family Residential Compliance Manual, chapter 9.

The manual lists a few exceptions: ducts already sealed, tested and certified by a rater, duct systems with less than 40 feet of duct, and ducts that contain asbestos. A contractor who meets these targets has to find and seal the leaks first, which is real work; our guide to leaky ducts explains what that involves.

Three permit follow-ups are worth asking:

1. Is the permit in the bid, and in whose name will it be pulled?
2. Who books the ECC-Rater? The CEC notes that the homeowner has the right to hire a rater who is independent of the contractor.
3. Will I get the compliance paperwork? Title 24 requires that completed documentation be left in the home for the building owner (CEC).

On AC installs, Alpha Mechanical pulls the city permit and handles the Title 24 testing as part of the job, as our AC installation page sets out; the same questions apply to a furnace replacement.

7. Read the Contract Before You Sign

California requires a written contract for any home improvement project over $500 in combined labor and materials. CSLB says the contract should detail "the work, price, when payments will be made, who gets the necessary building permits, and when the job will be finished," and must identify the contractor with their address and license number (CSLB, contracts). ENERGY STAR adds model numbers, the job schedule and warranty information to that list (ENERGY STAR).

Four CSLB rules protect you at signing:

• The down payment cap. By law, a contractor "cannot ask for a down payment of more than 10% of the contract price on a home improvement project or $1,000, whichever is less" (CSLB). The only exception is a contractor with a Blanket Performance and Payment Bond on file with CSLB. CSLB says only about two dozen licensees have one, and it shows on the license page.
• The three-day right to cancel. You may cancel within three days of signing, in writing, mailed before midnight of the third day (CSLB, contracts).
• No blank spaces. Never sign a blank or partially blank contract, and keep a copy.
• Changes in writing. Added or removed work, swapped equipment or a new finish date goes on a signed change order, with any price change.

Paying for a heat pump through a rebate or a loan adds one more check. SMUD's heat pump HVAC rebates must be submitted by "a qualified participating contractor through the SMUD Contractor Network," so ask whether the contractor is in it before you sign (SMUD, heating and cooling rebates). GoGreen Financing is different: it's California's financing program for energy upgrades, including HVAC, and the loan is an arrangement between you and the lender, not a rebate (GoGreen Financing). Our financing page explains how it works with an Alpha Mechanical install.

8. Call References and Listen for Repair Options

ENERGY STAR suggests asking friends, neighbors and co-workers for referrals, then asking each contractor for customer references and calling them about "the contractor's installation or service performance, and if the job was completed on time and within budget" (ENERGY STAR). Useful questions for a reference:

1. Did the crew arrive when promised?
2. Was the final price the price in the contract?
3. Did they pull a permit, and did the system pass its inspection and duct test?
4. Did they test the system and explain how to run it before they left?
5. Would you call them again for a repair?

Then listen to how each contractor talks about your current system. For example, a contractor who explains whether a repair still makes sense, and why, is giving you something a replacement-only pitch doesn't. Our repair or replace guide and the HVAC replacement guidelines set out the questions behind that call, and the common HVAC sales claims are worth reading before the first estimate.

Red Flags and What to Do If a Job Goes Wrong

Walk away, or slow down, when you see any of these:

• The license number is missing from the bid, or the name on the CSLB record doesn't match the company.
• The license is anything other than current and active, or the workers' comp line is blank (CSLB requires a policy or a self-insurance certificate on every active C-20 license).
• A down payment request above $1,000 or 10% of the price, whichever is less, with no blanket bond on the CSLB record.
• A bid far below the others, especially one that quietly leaves out the permit and the duct test. For example, a quote with no permit line is a smaller job, not a better price.
• "We don't need a permit for this" on an equipment change-out, with no reason you can confirm with your city or county building department.
• Pressure to sign the same day.

If something goes wrong after the work, the CEC's advice is to contact the installer first, and if the issue persists, contact CSLB, which licenses and regulates contractors and takes complaints (CEC). If you just signed and changed your mind, the three-day cancellation notice from check 7 is the faster route.

The Bottom Line

Choose a heating and air conditioning contractor the way an inspector would. Check the license, bond and workers' comp on the CSLB record first. Then look for a real home evaluation, three written bids for the same scope and a clear answer on the permit and the duct test. Sign only a contract that follows California's down payment and cancellation rules. Alpha Mechanical (CSL# 967727) is a licensed C-20 contractor based in Fair Oaks serving homes across Greater Sacramento, and every check in this guide applies to us too. Each rule above comes from the CSLB, CEC, ENERGY STAR, EPA, SMUD or GoGreen page it cites, and the NATE note from NATE's own site; the fact check against those pages was done on October 14, 2026. More about us, including the license link, is on our about page. When you're ready, request an estimate.

Frequently Asked Questions

What certifications should a reputable HVAC company have?

In California, start with a current, active CSLB license, normally in the C-20 class for heating and air conditioning work, which you can check on the CSLB website along with the contractor's bond and workers' compensation. Technicians who work on refrigerant circuits should hold EPA Section 608 certification. Look for NATE-certified technicians too; NATE is an industry certification that adds to the license check rather than replacing it.

How can I verify the reputation of an HVAC company?

Start with the CSLB license page, which shows the license status and any disclosable complaints or judgments. Then ask for customer references and call them about timing, budget and whether the job passed its permit inspection, and read reviews across more than one site. Consistent feedback across sources is the best signal.

What should a good HVAC installation contract include?

A written contract for any home improvement job over $500 that names the work, the equipment by model number, the total price, the payment schedule, who pulls the permit and when the job will be finished, along with the contractor's address and license number. The down payment can't exceed $1,000 or 10% of the price, whichever is less, and you can cancel in writing within three days of signing.

Should you buy an AC from a manufacturer or a contractor?

Whichever you buy from, line up the licensed installer first, because the installer's work is what the permit and the duct test check. In California, replacing an AC or heat pump outdoor unit, an air handler or a coil triggers Title 24 duct sealing and a leakage test verified by an ECC-Rater, with a few exceptions, and the CEC says properly permitted work will trigger any necessary testing. Check the installer's C-20 license on the CSLB site, and get a written bid that names the model number and a labor warranty in writing, separate from the manufacturer's parts warranty.