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Choosing an air cleaner in California
Filters, room units, electronic cleaners — they do different jobs, and California has rules about some of them. Pick what you're trying to fix to see where we'd start.
Find your starting point
Start with a better filter
Most homes do well with a pleated filter in the MERV 8–13 range. Higher numbers catch finer particles but resist airflow, so we measure your system's pressure before going up.
- A 4–5 inch media cabinet lasts longer and restricts less than a thin high-MERV filter.
- Seal leaky return ducts, or they pull in attic dust around the filter.
A MERV 13 filter plus a room unit
On smoke days, a MERV 13 filter — where your system can move air through it — with the fan running helps the whole house. A portable HEPA unit in the bedroom gives you one cleaner room overnight.
- Keep windows shut and avoid bringing in outside air while smoke is heavy.
- Change the filter after a long smoke event; it loads up quickly.
A portable unit sized to the room
Look for the clean air delivery rate (CADR) on the box. A common rule of thumb: smoke CADR of at least two-thirds of the room's floor area in square feet, for an 8-foot ceiling.
Ventilation before filtration
Particle filters don't remove smells well. A range hood vented outdoors, bathroom fans that actually move air and a steady supply of fresh air come first; activated-carbon filters can help after that.
- Avoid devices that make ozone to "freshen" air. Ozone generators sold as air purifiers are banned in California.
Filters, outside air, then room units
Use the highest filter grade your rooftop or split system can handle, and check the outside-air damper is actually open and set. Portable units help in waiting rooms and closed offices.
- Electronic air cleaners in a business follow the same CARB rules as at home.
- Put filter changes on a schedule and log them per unit.
What each kind of air cleaner does
Pleated filters
Rated by MERV. Catch dust and pollen as air passes through the system. Higher MERV means finer particles and more resistance.
Media cabinets
A deeper filter housing at the return. More surface area, so better capture with less airflow loss and fewer changes.
Portable HEPA units
Clean one room. Size them by CADR and run them on a setting you can live with — a quiet unit left on beats a loud one switched off.
Electronic cleaners
Ionizers, electrostatic precipitators and "plasma" devices, portable or in the ducts. They can produce ozone, so they must be certified to sell in California.
UV lamps
Mostly used to keep the indoor coil clean. Choose ozone-free lamps, and ask for the certification where the device falls under CARB's rules.
Ventilation
Exhaust fans and fresh-air supply remove what filters can't, such as cooking smells and stale air.
The California rule, in short
The California Air Resources Board (CARB) limits the ozone that air cleaning devices may emit to 0.050 parts per million, and devices covered by the rule must be certified before they can be sold here — including electronic units installed in ductwork.
Ozone generators marketed as air purifiers can't be sold in California at all. Before buying, check the exact model on CARB's air cleaner page.
