HVAC (C-20) · Lesson 6 of 6

Whole-Dwelling Ventilation Rate (Energy Code Equation 150.0-B)

"Whole-Dwelling Ventilation Rate (Energy Code Equation 150.0-B)" is lesson 6 of 6 in the HVAC (C-20) Learning Hub. It opens with "Tight Homes Need Mechanical Ventilation" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. Tight Homes Need Mechanical Ventilation
  2. The Equation
  3. If the Central Fan Is Used (CFI)
  4. Infiltration Credit Is a Separate Calculation
  5. Select the Fan and Place It Right

The worked example in the course applies this lesson to a realistic job in 5 steps, moving through "Write the equation", "Area term", "Bedroom term", and "Compare the fans".

What you'll be able to do

  • Explain the main idea of "Whole-Dwelling Ventilation Rate (Energy Code Equation 150.0-B)" in plain language you can use on the exam.
  • Apply this step with confidence: "If the Central Fan Is Used (CFI)".
  • Apply this step with confidence: "Infiltration Credit Is a Separate Calculation".
  • Apply this step with confidence: "Select the Fan and Place It Right".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Whole-Dwelling Ventilation: Qtot Calculation2,100 sq ft conditioned, 3 bedroomsBR 1BR 2BR 3LIVING / KITCHENFANFan must deliver at least 93 CFMEquation 150.0-BQtot = 0.03 x Afloor + 7.5 x (Nbr + 1)Area term: 0.03 x 2,100 = 63Bedroom term: 7.5 x (3 + 1) = 30Qtot = 63 + 30 = 93 CFMFan A: 80 CFM rated = FAILFan B: 110 CFM rated = OKStudio check, 600 sq ft, Nbr = 1:0.03 x 600 + 7.5 x 2 = 33 CFMRequired whole-dwelling ventilation: 93 CFMNo infiltration credit taken. Pick a fan rated for at least 93 CFM.2025 California Energy Code Section 150.0(o)1C(i), Equation 150.0-B.CC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: Tight Homes Need Mechanical Ventilation

New California homes are built tight, so fresh air does not leak in on its own. California Energy Code Section 150.0(o) requires every dwelling unit to have whole-dwelling mechanical ventilation, and Section 150.0(o)1C(i) prints the equation for the total required rate. Window operation is not a permissible way to provide it (150.0(o)1A). HVAC contractors install or size the ventilation fan, or the outside-air duct on the central system, so this calculation is part of the job.

Step 2: The Equation

The total required airflow is Qtot = 0.03 x Afloor + 7.5 x (Nbr + 1), in CFM (Section 150.0(o)1C(i), Equation 150.0-B). Afloor is the dwelling-unit floor area in square feet. Nbr is the number of bedrooms and is not to be less than 1, so a studio is counted as one bedroom.

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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