The Surprise Bill After Your Workers' Comp Audit: Class Codes, 1099 Techs, and How to Prepare

The workers' comp audit shows up 30 to 60 days after the policy year ends, usually as a form or a scheduled call. Six weeks later the invoice arrives, and for a shop that added a helper and used a subcontractor for two ductwork jobs, it can run into four figures on a year the owner had already mentally closed. Nothing fraudulent happened. The policy was priced off estimated payroll, the audit measures actual payroll, and the gap between them is billable either direction.

Most owners understand that part. What surprises them is that the biggest line items on an audit bill often have nothing to do with how much payroll they ran.

They have to do with how it was labeled.

How appliance and HVAC work gets split between workers' comp class codes

Workers' comp rates are quoted per $100 of payroll, per classification. Most of the country uses classifications published by the National Council on Compensation Insurance, and two codes cover almost everything a residential service company does.

NCCI's phraseology for 5537 is "Heating, Ventilation, Air-Conditioning, and Refrigeration Systems, Installation, Service and Repair, Shop, Yard & Drivers." Its scope describes an all-inclusive classification for nonportable forced air heating, ventilation, air conditioning and evaporative cooling systems, and it absorbs the electrical wiring, plumbing and sheet metal work when the same contractor performs it at the same job.

Code 9519 reads "Household and Commercial Appliances, Electrical, Installation, Service or Repair & Drivers." Its scope covers electrical household and commercial appliance work, naming machines like washing machines, refrigerators, dishwashers and electric ovens, and it takes in shop employees, outside service employees and incidental parts department staff.

The boundary between them is where audits go sideways, and NCCI drew it with cross-references rather than with a clean line. Portable air conditioning units are separately rated to 9519. Refrigeration units cleaned, oiled, adjusted or serviced in conjunction with an air conditioning system go to 5537. Audio, video and related electronics work goes to 9516 instead.

One caution before you argue a code with an auditor. Individual states can and do modify NCCI's national scopes, and the published scope pages carry revision dates going back years, so confirm the current version that applies in your state rather than the one that turns up first in a search.

The two line items that create the bill

The first is unsplit payroll. Travelers states the rule on its premium audit page directly: "If records don't show the actual payroll applicable to each classification, the entire payroll of the individual employee must be assigned to the highest-rated classification that represents any part of his/her work." The carrier adds that estimated or percentage allocations are not accepted, and that actual time records by job classification are what allow a split.

Read that as an operations instruction, not an insurance one. A tech who runs appliance calls four days a week and helps on a condenser changeout on Fridays can be billed at the higher-rated code for all five days if nobody wrote down which day was which. The fix is dispatch data you already generate. Most field software can tag a job type and export hours by tag, and an auditor will accept that far more readily than an owner's recollection in April.

The second line item is subcontractors. Travelers again: "Without a valid Certificate of Workers Compensation Insurance we may charge a premium for work performed by an independent contractor/subcontractor." Auditors pull the cash disbursements journal and the 1099s, and any payment to a person or company without a certificate covering the term of the work is a candidate to be treated as your payroll.

One detail matters more than the rest. The certificate has to cover the dates the work was actually performed, so one collected in January does nothing for a job worked the previous August. Collect at engagement, re-collect at renewal, and keep them in the same folder you already maintain for the additional insured paperwork your commercial clients demand.

Refusing the audit is the expensive option

Owners who dread the number sometimes stop answering. That is the one move with a published price.

Berkshire Hathaway Homestate Companies states on its premium audit page that non-compliance with the audit process "can result in the cancellation of your current policy and a charge of up to three times your estimated annual premium, in accordance with audit noncompliance charge (ANC) rules from the National Council on Compensation Insurance (NCCI) and the ANC endorsement on your policy." Whether a carrier applies that depends on the endorsement attached to your policy and your state's adopted rules, so read your own endorsement rather than assuming.

Losing the policy is the worse half of that sentence. A cancellation for non-compliance follows you into the next submission.

California runs its own system

California does not use NCCI. The state has its own rating bureau, the Workers' Compensation Insurance Rating Bureau of California, with its own classification system, so the code numbers and scope language above do not map one for one. A California shop should have its broker pull the actual WCIRB classification rather than reasoning from national codes.

The rate backdrop there moved this year. The California Department of Insurance announced on July 10, 2026 that Commissioner Ricardo Lara adopted advisory pure premium rates averaging $1.65 per $100 of payroll effective September 1, 2026, a 6.6% increase over the rates approved for 2025. WCIRB had asked for 10.4%. The department attributed the increase to higher medical treatment and medical-legal costs, more projected cumulative trauma claims, and rising claim adjusting costs.

One word in that announcement does most of the work: advisory. As the release puts it, "The adopted rate is advisory, meaning that insurance companies are not bound by it and are free to set their own rates." It is a benchmark for loss costs, not a price. Your carrier's filed rates, your experience and your classification decide what you pay, which is why two California shops in the same trade can see very different renewals in a year the benchmark rose 6.6%.

If California is your market, the state's coverage mandate timeline is the other thing to have straight, and we covered that in the piece on SB 216 and contractor workers' comp requirements.

What to have ready before the auditor calls

Pull together payroll reports for the policy term, quarterly 941s, state unemployment wage reports, your general ledger and cash disbursements journal, all 1099s and the 1096, certificates of insurance for every subcontractor, and whatever job-level hour records you can produce by class. Berkshire Hathaway's list and Travelers' list overlap almost completely, which tells you this is standard practice rather than one carrier being difficult.

Then do the part most owners skip: reconcile your own numbers first. Total the payroll by class, total subcontractor payments, and find the coverage gaps before the auditor does. An audit you walk into with a reconciled worksheet takes an hour. One you walk into cold takes three and ends with assumptions made in the carrier's favor.

Overtime is worth checking too. Travelers says overtime can be excluded from premium if separate records are kept, using one-third of the overtime when it is paid at time and a half and one-half when it is paid at double time, and notes the exclusion does not apply to workers' comp in Delaware or Pennsylvania. Other carriers and states handle it differently, so ask yours.

The 1099 question sitting under all of this is a legal one, not an insurance one. Whether a tech is properly an independent contractor is decided by state labor law, and in California that means the ABC test codified by AB 5. Getting it wrong costs more than an audit bill. Put it in front of a CPA and an employment attorney licensed in your state before the next hire, and read it alongside the mechanics in the first technician hiring guide and the multi-truck scaling guide.

Everything above describes general practice and published carrier language. Classification rules, audit rights and noncompliance penalties vary by carrier, by policy form and by state, and nothing here tells you what your policy provides or promises how a specific audit will come out. Have a licensed broker review your classifications before renewal and an attorney review any worker-status question. If you want a rough range to plan against in the meantime, the insurance cost estimator and the state requirements pages are built for exactly that.

Sources

National Council on Compensation Insurance. "Scopes Manual, Code 5537: Heating, Ventilation, Air-Conditioning, and Refrigeration Systems, Installation, Service and Repair, Shop, Yard & Drivers." ncci.com

National Council on Compensation Insurance. "Scopes Manual, Code 9519: Household and Commercial Appliances, Electrical, Installation, Service or Repair & Drivers." ncci.com

Travelers. "Workers Compensation Premium Audit." travelers.com

Berkshire Hathaway Homestate Companies. "Premium Audit." bhhc.com

California Department of Insurance. (2026). "Commissioner Lara takes action to maintain stable workers' compensation market amid rising costs," July 10, 2026. insurance.ca.gov