California Climate Zone 2
Climate zone 2 covers the inland North Bay and wine country, a step warmer than the bay shore and cooler than the valley floor. The Energy Commission assigns 119 of California's ZIP codes to it, making it the 11th largest of the sixteen.
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Where zone 2 is
The Energy Commission assigns 119 ZIP codes to zone 2 — about 4.4 per cent of every ZIP code it lists, and the 11th largest of the sixteen. Places in it include Santa Rosa, Napa, San Rafael, Petaluma, Ukiah and Sonoma.
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 945xx, 949xx, 954xx, 955xx.
What drives compliance in zone 2
Both loads matter, which makes this one of the harder zones to design for. Inland North Bay summers are warm enough that cooling has to be taken seriously, while winters are cool enough that heating cannot be treated as an afterthought. A design tuned only for one of the two tends to fall short on the other.
Where zone 2 ends
The zone 2 boundary with the bay shore runs through Marin, and it is unusually tight: Corte Madera sits in zone 3 while Larkspur, immediately next to it, sits in zone 2. Two adjacent towns on opposite sides of the assignment is about as compact as any boundary in the state.
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.