Whole-House Fan or Attic Fan in Los Angeles?

How much passive vent area an attic needs is in attic ventilation requirements.

A whole-house fan is also different from the small continuous fan the Energy Code calls whole-dwelling mechanical ventilation, which is there for indoor air quality, not cooling.

By those thresholds, the west Valley fits well, though the Pierce College station sits on the valley floor and hillside homes can run warmer at night; Burbank and the eastern Valley pass the California guide's test but not the Solution Center's 25°F swing; the Antelope Valley has the swing but warmer nights; downtown and the coast fall short. A whole-house fan doesn't filter or dry the air, so it's no help on smoky or humid nights; it can't cool when the night stays hot, as in a heat wave or a Santa Ana event; and it means windows open at night.

California's Energy Code draws a coarser line: for new single-family homes on the prescriptive path, it lists a whole-house fan in climate zones 8 to 14, which take in downtown and South Los Angeles as well as the Valley and the Antelope Valley, and not coastal zone 6 (Energy Code §150.1(c)12, Table 150.1-A). Your own nights matter more than the zone. It isn't required on the performance path, on additions of 1,000 sq ft or less, on new homes of 500 sq ft or less, or for existing homes, and a re-roof never triggers it.

• Airflow. The Energy Code's prescriptive rule for new homes is at least 1.5 cfm per square foot of conditioned floor area, using the airflow listed by the Home Ventilating Institute, not a number from the box; a 2,000 sq ft house needs about 3,000 cfm. That's a minimum: the Building America Solution Center's range works out to about 1.5 to 3 cfm per square foot with 8-foot ceilings, sized by the house's volume, and most recommendations sit at the higher end.
• Attic vents. At least 1 square foot of attic net free vent area for every 750 cfm of fan, or more if the fan's maker specifies more, unless the fan is ducted straight outdoors (§150.1(c)12B). For 3,000 cfm that's 4 sq ft, or 576 square inches. Size the vents from the fan you actually buy. Too little vent area cuts the airflow and can push hot attic air back into the house.
• Net free area, not vent size. Screens and louvers block part of every vent; the Energy Commission's compliance manual counts an insect-screened vent at half its open area. Use the net free area the vent's maker lists.
• Windows. Building America recommends opening at least 4 square feet of screened window for every 1,000 cfm, counting only the part of the window that opens; on a sliding window that's typically a third to a half of it.
• Winter. The fan is a hole in the ceiling. If it doesn't come with an insulated cover or damper, the Solution Center recommends adding one to cut heat loss when the fan is off.

On a one-story house the attic venting the code already requires often covers the fan; on a two-story house with a small attic it may not. A 2,500 sq ft two-story house with a 1,250 sq ft attic needs 4.2 sq ft of vent area if it's vented at the residential code's 1/300 option, which requires 40 to 50 percent of the vents high, but a 3,750 cfm fan needs 5 sq ft. A re-roof is the time to add vents if the numbers come up short; add low and high vents together so the high share stays at 40 to 50 percent. A house with no attic, under a cathedral or flat ceiling, can't use an attic fan, and a ceiling whole-house fan has nowhere to exhaust; Building America calls such homes very difficult or expensive to fit, and the options are a fan mounted in an exterior wall or one ducted straight outdoors.

• Little saving. Researchers at the Florida Solar Energy Center measured about a 6% cut in cooling, about 460 kWh a year, from two solar-powered attic fans in a Florida home that already had a radiant barrier; attic air peaked more than 20°F cooler, but at Florida's 2000 electricity prices the saving was worth about $37 a year against about $850 installed, a payback of over 20 years. They noted the saving could be larger without a radiant barrier, with less ceiling insulation or with the air handler in the attic. Older studies of line-powered attic fans that they reviewed found the fan used more electricity than it saved unless the attic was uninsulated.
• Cooled air pulled out. A 1994 field study of houses in North Carolina measured attic fans drawing an average of 231 cfm of air from the living space into the attic.
• What works better. Attic insulation and air sealing, a radiant barrier, or a cooler roof surface; see attic insulation when you replace the roof and radiant barriers in Los Angeles attics.

1. Check the nights. A whole-house fan works best where summer nights are cool and the swing is large; on the coast it does much less.
2. Size it from the listing. Use the HVI-listed airflow; 1.5 cfm per sq ft of floor area is the code minimum for new homes, and many retrofit fans are larger.
3. Count the vents. Add up the attic's net free vent area and compare it with 1 sq ft per 750 cfm of the fan you buy, or the maker's figure if it's higher; plan new vents with the roof.
4. Check gas appliances. If any gas appliance is in the attic or inside the house, or has a standing pilot light, have a combustion-safety check before you buy; it can rule out a whole-house fan.
5. Ask about permits and rebates. It's electrical work and a ceiling opening: in the City of Los Angeles, ask LADBS which permit applies; Burbank, Glendale, Pasadena, Santa Clarita, Palmdale, Lancaster and unincorporated LA County each have their own building department. If LADWP is your utility, its October 2025 program summary lists a $200 rebate per whole-house fan; other utilities set their own programs, so check the current terms before you buy.

Code sections, rules and figures on this page come from the primary sources below. Codes, local requirements and product terms change; each was verified October 15, 2026.

1. California Energy Commission, 2025 Building Energy Efficiency Standards (Title 24, Part 6), CEC-400-2025-010, sections 100.1, 150.1(b),…
2. California Energy Commission, 2025 Single-Family Residential Compliance Manual, CEC-400-2025-005
3. California Energy Commission, 2022 Single-Family Residential Compliance Manual, Chapter 4, section 4.7.10
4. California Energy Commission, Building Climate Zones by ZIP Code
5. California State Fire Marshal, Fire Hazard Severity Zones
6. California Residential Code 2025, Section R806 (UpCodes)
7. California Wildland-Urban Interface Code 2025, Section 504.10 (UpCodes)
8. Building America Solution Center, Attic Ventilation Fans (updated September 21, 2022)
9. Building America Solution Center, Whole-House Fans (updated September 29, 2022)
10. Building America, Measure Guideline: Ventilation Cooling (2012)
11. U.S. Department of Energy, Whole House Fan technology fact sheet (1999)
12. Parker and Sherwin, Performance Assessment of Photovoltaic Attic Ventilator Fans, FSEC-GP-171-00
13. Parker, Literature Review of the Impact and Need for Attic Ventilation in Florida Homes, FSEC-CR-1496-05
14. Tooley and Davis, Powered Attic Ventilators, ACEEE Summer Study 1994
15. NOAA NCEI, U.S. Climate Normals 1991–2020
16. LADWP program summary with electrification measures (October 2025), hosted by LADBS