Why California HERS Testing Fails And How to Avoid an Expensive Re-Test

A failed HERS test is rarely about your equipment. It is almost always about how the system was installed and whether your contractor planned for the test from day one. HERS testing is third-party verification required under California Title 24 for most HVAC changeouts, and a fail means rework, a re-test fee, and a delayed final inspection. Here is why these tests fail in Nevada County and Placer County homes, and how to make sure yours passes the first time.

What a HERS Test Actually Checks

HERS stands for Home Energy Rating System. It is field verification performed by an independent, state-certified HERS rater who confirms your installed system matches what was modeled in the Title 24 paperwork. The rater does not work for your contractor. That independence is the point. Depending on your equipment, climate zone, and what was replaced, the rater verifies some combination of four things: duct leakage, refrigerant charge, airflow across the coil, and fan watt draw. The work flows through three forms: the CF-1R (the design), the CF-2R (what the installer measured and signed off), and the CF-3R (what the rater independently confirmed). A test fails when the rater's numbers do not match the standard the design promised.

Reason 1: Duct Leakage Over the Limit

Leaky ducts are the most common reason a HERS test fails in older Sierra foothill homes. The rater seals and pressurizes your duct system, then measures exactly how much air escapes. Homes around Grass Valley, Nevada City, and Penn Valley often have decades-old ductwork in crawl spaces and attics where connections have loosened over time. The usual culprits are unsealed boot-to-drywall gaps, flex duct that was never double-clamped, open seams at the air handler cabinet, and return leaks at framing. One detail trips up budget installers constantly: standard gray cloth duct tape is not code-legal on ducts. Only mastic or UL-listed foil tape passes. If your installer sealed with the wrong product, the rater flags it and you re-test. The fix is sealing the system correctly before the rater ever arrives. See our AC installation and furnace installation pages for how we handle ductwork.

Reason 2: Refrigerant Charge Off by a Hair

On air conditioners and heat pumps in certain climate zones, the rater verifies refrigerant charge. A system can cool your house and still fail this test. The rater attaches their own gauges and confirms the charge matches the manufacturer's specification within a tight tolerance, measuring superheat or subcooling depending on the metering device. Overcharged and undercharged systems both fail, and both quietly cost you in efficiency and equipment life. The failure almost always traces back to an installer who eyeballed the charge or skipped the measurement the CF-2R requires. A technician who charges by the numbers, then documents it, gives the rater nothing to flag. This is exactly what NATE-certified training is built to prevent, and our AC repair team handles charge verification the same way on every changeout.

Reason 3: Airflow Too Low and Fan Working Too Hard

Two related tests catch the same underlying problem: a duct system that cannot move enough air. For the airflow check, the rater measures actual delivery across the coil and compares it to the design value. A dirty or clogged filter is a frequent, avoidable cause, so the rater will have filters pulled before testing. The deeper cause is usually a restrictive or undersized duct system that no new furnace or condenser can fix on its own. The fan watt draw test measures how hard the blower works to move that air. A fan pulling too many watts per unit of airflow signals ducts that are fighting the system. When airflow fails, it is sometimes not the installer's fault at all. If the duct system was out of scope, the home may need duct upgrades to comply. The right move is catching this in the planning stage, before the equipment goes in, not after a failed test.

The Real Reason Most Tests Fail: No Plan for the Test

Step back and the pattern is clear. Duct leakage, charge, airflow, fan watt draw. Every common failure comes from the same root: a contractor who treated the HERS test as someone else's problem. The systems that pass are designed and installed with the test in mind. Ducts sealed with the right materials. Charge measured and recorded, not guessed. Duct capacity checked against the equipment before anything is bolted in. The installer fills out the CF-2R honestly so the rater's CF-3R lines up. A cheap install that ignores all of this is not a bargain. It is a re-test fee, a second visit, and weeks added to your final inspection. The way to avoid a failed HERS test is to hire the kind of contractor who never lets one happen.

What Happens If You Still Fail

A failed test is not the end of the project, but it costs time and money. Usually the contractor corrects the issue, then the rater returns and re-tests, and you pay for that second visit. In some cases the answer is on paper rather than in the field: if installed conditions differ from the original design, the Title 24 energy model can sometimes be updated to reflect real field conditions, which can resolve a borderline result without tearing anything apart. A good contractor knows which path applies and handles the coordination with the rater for you.

• Field fix: seal ducts, correct charge, or improve airflow, then re-test.
• Paper fix: update the Title 24 report to match verified field conditions where allowed.
• Either way: you should not be left chasing the rater yourself.

If a HERS upgrade points toward duct or equipment work, our financing options can help spread the cost.

Related: HERS testing requirements, HERS testing and project delays, AC installation.