CSLB C-20 HVAC ContractorVentilation and Air DistributionMedium
A bathroom in new residential construction has no operable window. According to California Mechanical Code ventilation requirements, what minimum mechanical exhaust rate satisfies code if the fan runs continuously?
- A75 CFM continuous
- B20 CFM continuous
- C50 CFM continuous
- D10 CFM continuous
Show answer & explanationAnswer & explanation
Correct answer: B. 20 CFM continuous
When a bathroom lacks an operable window, mechanical ventilation is required: 50 CFM if intermittent (fan cycles with light or occupancy) or 20 CFM if run continuously, per CMC/ASHRAE 62.2 requirements.
Why the other options are wrong
- A. 75 CFM exceeds the code minimum unnecessarily.
- C. 50 CFM applies to intermittent, not continuous, operation.
- D. 10 CFM is below the code-minimum continuous rate.
Bathroom Exhaust Ventilation
Mechanical code requirement for bathroom exhaust when no operable window exists: 50 CFM intermittent or 20 CFM continuous.
- Based on ASHRAE 62.2 residential ventilation standard
- Continuous fans run at lower CFM than intermittent
- Must exhaust directly to outdoors, not into attic
Memory trick: Fifty if it stops, twenty if it never drops.