CSLB C-20 HVAC ContractorVentilation and Air DistributionEasy
Per California Title 24/CALGreen requirements, a bathroom exhaust fan intended for continuous whole-house ventilation operation must have a maximum sound rating, when tested at 0.25 in. w.c., of no more than how many sones?
- A3.0 sones
- B0.5 sone
- C1.0 sone
- D5.0 sones
Show answer & explanationAnswer & explanation
Correct answer: C. 1.0 sone
CALGreen and ASHRAE 62.2 require exhaust fans used for continuous whole-house ventilation to be rated at 1.0 sone or less to minimize occupant annoyance from continuous operation, encouraging occupants to leave the fan running.
Why the other options are wrong
- A. 3.0 sones is closer to the allowance for intermittent local exhaust fans, not continuous systems.
- B. No standard requires such an aggressively low rating for typical bath fans.
- D. 5.0 sones would be excessively loud and would discourage continuous operation, defeating ventilation compliance intent.
Exhaust Fan Sone Rating
Sones measure perceived loudness of exhaust fans; continuous whole-house ventilation fans must be quiet (≤1.0 sone) so occupants do not disable them.
- 1 sone ≈ quiet refrigerator hum
- Continuous whole-house fans: max 1.0 sone
- Intermittent local exhaust fans allow higher sone ratings (up to 3.0)
Memory trick: 'Quiet fans keep running, loud fans get turned off.'