Which zone you're in
California sets building energy rules by climate zone, and your zone is determined by ZIP code or street address, not just city name. San Diego, Chula Vista and Oceanside are in Climate Zone 7. Escondido, El Cajon and Temecula are in Climate Zone 10. Check your ZIP on the California Energy Commission's climate zone map.
Coastal Climate Zone 7
Cooling loads are modest and heating loads are small, which makes right-sizing important: an oversized system short-cycles and leaves rooms clammy. Salt air is the main threat to equipment near the beach, so coated condenser coils, corrosion-resistant hardware and annual coil rinsing matter. A heat pump often covers heating and cooling for the whole year.
Inland Climate Zone 10
Long hot summers put real load on equipment and on attic ductwork. Duct leakage and insulation often decide comfort more than the equipment brand. Climate Zone 10 cities publish alteration checklists; Escondido's calls for R-8 duct insulation on altered and new duct systems and MERV 13 filters on fully replaced systems with more than 10 feet of ducting. EER2, the hot-condition efficiency rating, is worth comparing alongside SEER2.
What stays the same
In both zones, replacing a refrigerant-containing component or the air handler makes the system an altered system under the Energy Code, which generally triggers HERS duct leakage testing. And in both, the best first step is a load calculation, not a quote that simply matches the old unit's size.
Keep reading
Looking for city-specific rules? See our SoCal city guides.
Sources
Last checked October 2026.