HVAC (C-20) · Lesson 1 of 6

Airflow per Ton and Fan Efficacy: The Title 24 Verification Numbers

"Airflow per Ton and Fan Efficacy: The Title 24 Verification Numbers" is lesson 1 of 6 in the HVAC (C-20) Learning Hub. It opens with "Airflow Is Verified by Test" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. Airflow Is Verified by Test
  2. The Airflow Minimums
  3. Fan Efficacy in Watts per CFM
  4. Build In the Test Access
  5. Alterations and the Charge Check

The worked example in the course applies this lesson to a realistic job in 5 steps, from "Find the minimum airflow" through "Turn the limits into watts".

What you'll be able to do

  • Explain the main idea of "Airflow per Ton and Fan Efficacy: The Title 24 Verification Numbers" in plain language you can use on the exam.
  • Apply this step with confidence: "Fan Efficacy in Watts per CFM".
  • Apply this step with confidence: "Build In the Test Access".
  • Apply this step with confidence: "Alterations and the Charge Check".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Airflow per Ton and Fan Efficacy3-ton ducted split, gas furnace air handlerSUPPLY PLENUMStatic-pressureprobe holeEVAP. COILBLOWER470 WRETURN1,100 CFMFan efficacy = watts / CFMNot to scaleSection 150.0(m)13B: 3 tonsMinimum: 3 x 350 = 1,050 CFMTest 1: 1,020 CFM, below 1,050: FAILRetest: 1,100 CFM at 470 WAirflow 1,100 is at least 1,050: OKEfficacy = 470 / 1,100 = 0.427Gas furnace limit 0.45: OKGas furnace: 0.45 x 1,100 = 495 W maxNot gas furnace: 0.58 x 1,100 = 638 WSmall duct high velocity: 250 CFM/tonRetest passes: 1,100 CFM (needs 1,050) and 0.427 W/CFM (limit 0.45)Altered system (refrigerant parts replaced): minimum is 3 x 300 = 900 CFM.2025 California Energy Code Section 150.0(m)13B; Section 150.2(b)1Fii(a) for altered systems.CC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: Airflow Is Verified by Test

The 2025 California Energy Code, Section 150.0(m)13, applies to dwelling space-conditioning systems that use forced-air ducts to supply cooling. The installer must demonstrate both the airflow across the system and the air-handler fan efficacy by field verification and diagnostic testing. The test procedure is in Reference Residential Appendix RA3.3, which the Energy Code cites; this lesson uses the numbers the Energy Code itself prints.

Step 2: The Airflow Minimums

A single-zone central forced-air system must demonstrate, in every control mode, airflow of at least 350 CFM per ton of nominal cooling capacity through the return grilles (Section 150.0(m)13B). A zonally controlled system must deliver at least 350 CFM per ton in every zonal control mode (13C). A small duct high velocity system needs at least 250 CFM per ton (13D). Nominal capacity is the rated size, so a 4-ton system needs 4 x 350 = 1,400 CFM.

The remaining 3 steps, the worked example and the quiz are in the course. This is a preview. The full lesson, with the step-by-step explanations, a worked example and a quick-check quiz, is inside the classroom.

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