Does my bathroom fan need a humidity sensor?

Not under the Energy Code, which asks for an occupant on-off control or an automatic control that does not stop manual operation. CALGreen requires a humidity control in new homes and in additions or alterations that increase conditioned area, volume or size, unless the fan is part of the whole-house ventilation.

Does a bathroom with a window still need a fan?

Yes. Section 150.0(o)1G requires local mechanical exhaust in each bathroom and lists no exception for a window.

Can I replace a bathroom fan with a quieter one?

Yes, provided the new fan carries airflow and sound ratings. If a permit once required the fan to deliver a set airflow as the home's ventilation fan, the replacement must be rated at no less than that airflow.

Title 24 Bathroom Exhaust Fan Requirements

Every bathroom, a powder room included, needs a mechanical exhaust fan that vents outdoors. Section 150.0(o)1G allows two routes: a demand-controlled fan rated at 50 cfm or more, or a continuous fan rated at 20 cfm or more. A window does not replace the fan, because the rule lists no exception for one.

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What counts as a bathroom

Section 100.1 defines a bathroom as a room or area containing a sink used for personal hygiene, a toilet, a shower or a tub. CALGreen, the green code in Part 11, is narrower: for its purposes a bathroom has a bathtub, a shower or a tub-shower combination.

Choosing the route

Demand-controlled, 50 cfm or more. The occupant gets a readily accessible on-off control, or an automatic control that does not stop the occupant switching the fan on.
Continuous, 20 cfm or more in every hour. It runs through all occupiable hours, with a manual on-off control the occupant can reach. It may be part of a balanced ventilation system.

Reading the label

The fan must be rated for airflow under ASHRAE 62.2 Section 7.1 and for sound under Section 7.3, at no less than the airflow the code requires. The compliance manual sets the sound limits at 3 sones for a demand-controlled fan and 1 sone for a continuous one. Ratings are published in the Home Ventilating Institute directory.

Ducting it without a test

The installer must confirm the airflow delivered, either by measuring it with a flow hood or flow grid or by building to Table 150.0-H and having the work inspected. The table route needs the fan rated at 0.25 inch of water static pressure, no more than 25 feet of duct and three elbows, and an outdoor termination at least as large as the duct. A 50 cfm fan needs 4-inch duct, an 80 cfm fan 5-inch, and a 100 cfm fan 5-inch rigid or 6-inch flex, fully extended. A backdraft or automatic damper is required on any fan that moves air between the house and outdoors (Section 150.0(m)7).

Who inspects it

The building inspector looks at the duct and housing during framing and at the noise rating at final. An ECC-Rater does not test bathroom fans; the rater's ventilation checks are the whole-dwelling airflow and the kitchen hood rating.

Replacements, laundries and CALGreen

A new or replacement bathroom fan in an existing home meets the same rules (Section 150.2(b)1M). Part 6 asks for local exhaust in kitchens and bathrooms only, so a laundry room needs none, although a dryer must vent outdoors. CALGreen adds an ENERGY STAR fan ducted outside and a humidity control, unless the fan serves the whole-house ventilation, in new homes and in additions or alterations that increase conditioned area, volume or size.

Common Title 24 Questions

Frequently Asked Questions

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