Can an Open Window Replace the Bathroom Fan in a Pasadena Remodel? Not Once There Is a Shower
Short answer: no. If a bathroom has a tub or a shower, California's residential code wants a mechanical exhaust fan, and an operable window does not count as a substitute. That surprises Pasadena owners more than most, because so many older bathrooms here have a window, a lot of tile, and no fan at all.
What the code actually requires
The residential code says a bathroom with a bathtub, shower or tub-shower combination must be mechanically ventilated for humidity control, and it adds that window operation is not a permitted way to provide that exhaust (section R325.2.1 in the 2025 edition, which the California Residential Code text lists; handouts written for the 2022 edition cite it as R303.3). The 2025 bathroom handout from the City of Glendora boils the rest down to the same short list an inspector works from:
50 CFM on demand, or 20 CFM running continuously.
A humidity-sensing control (CALGreen section 4.506.1, part of the state's Green Building Standards Code).
An ENERGY STAR compliant fan.
Ducted to the outdoors, not into the attic.
Its own switch, separate from the lights, under the Title 24 energy standards.
One exception is worth knowing. A powder room with no tub or shower can still rely on a window of at least 3 square feet, half of it openable, plus a light.
Which Pasadena projects this reaches
Pasadena's City Council took up the 2025 California Building Standards Code at its November 3, 2025 meeting, and the City's staff report says the new codes apply to projects that file for a building permit on or after January 1, 2026. A bathroom remodel permitted this year is therefore reviewed against the 2025 codes. Glendora's handout lists the usual permit triggers: replacing or moving a toilet, sink or tub, replacing drywall, or altering the electrical. Nearly any remodel that opens the walls qualifies.
We did not find a Pasadena-specific bathroom handout, so treat the statewide code as the rule and confirm details for your address with the City's Permit Center before you buy a fan.
What we find in older Pasadena bathrooms
Our bathroom remodeling page describes what we run into again and again when we open a bathroom in an older house: no exhaust fan at all, or a fan that vents into the attic instead of outside. The windowed 1920s bathroom is the classic case, because the owner assumed the window was doing the job. It is not. The window is shut during a winter shower, and the moisture goes into plaster, paint and framing. That is part of why a bathroom that looks fine can still be rotting behind the tile, which we cover in our look at what a $10,000 bathroom really includes and in our guide to adding a bathroom.
Our call: pay for quiet, not for airflow
If we could change one thing about how people shop for a fan, it would be this: buy the quietest fan that meets the code, not the strongest one. A loud fan gets switched off, and a fan that is off protects nothing. For most bathrooms the 50 CFM minimum is enough, so the extra money is better spent on a low-noise unit with a humidity sensor and a short, straight duct run to the outside, insulated where it crosses cold attic space. We would also not accept a fan that terminates in the attic because the bathroom is small. The code does not make an exception for small.
The fan matters most when the shower surfaces change. If you are weighing tile against solid panels, the shower wall comparison covers that choice, and the fan keeps either one dry. For older houses, the Craftsman bungalow restoration guide shows where else moisture and age collide.
Before you hire anyone
Ask the contractor to name the fan model, the duct route and where it exits the house, and to write all three into the scope. Our remodeling contract checklist explains what else belongs in a proposal. If the work also touches the kitchen, the City may want more than a fan; see what a kitchen permit can trigger elsewhere in the house. Finished bathrooms from our crews are in the project gallery, and common questions are answered in our remodeling FAQ. For a whole-house plan, start with our whole-home remodel guide.
Call (626) 744-0402 or request a free in-home estimate. Pasadena Remodeler is the remodeling division of Handyman Connection of Pasadena, 110 S Rosemead Blvd, Pasadena, CA 91107, CSLB License No. 992200.
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