California Climate Zone 9

Climate zone 9 covers the Los Angeles basin, the San Fernando and San Gabriel valleys and the inland Los Angeles County plain. The Energy Commission assigns 350 of California's ZIP codes to it, making it the 2nd largest of the sixteen.

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Where zone 9 is

The Energy Commission assigns 350 ZIP codes to zone 9 — about 13.0 per cent of every ZIP code it lists, and the 2nd largest of the sixteen. Places in it include Los Angeles, Pasadena, Glendale, Burbank, Pomona, Santa Clarita, Simi Valley and West Covina.

The zone is geographically contiguous — it occupies one continuous block of the state rather than being scattered. The ZIP codes fall in the prefix ranges 900xx, 902xx, 906xx, 910xx, 911xx, 912xx, 913xx, 914xx, 915xx, 916xx, 917xx, 918xx, 930xx.

What drives compliance in zone 9

Cooling drives the result and heating is secondary. Hot inland summers across the basin and the valleys mean glazing area and orientation, duct location and cooling equipment efficiency carry most of the calculation. Ducts run in unconditioned attics are a common weak point here.

Where zone 9 ends

The second largest zone, covering the Los Angeles basin and the valleys behind it. The City of Los Angeles itself sits in zone 9 across much of its area while also reaching into three other zones, which is why a Los Angeles address says very little about which assignment applies.

Boundaries follow conditions rather than administrative lines, so the assignment is resolved from the project ZIP code rather than inferred from the city on the drawings.

Cities we cover in zone 9

3 of our city guides cover places in this zone, and some of them cross a zone boundary inside the city.