Best U-Factor and SHGC for Windows in California

Data updated October 12, 2026.

ENERGY STAR Version 7.0 splits California into 4 climate zones: South-Central, North-Central, Northern, Southern. The limits for each are in the table below. Check your address with the ENERGY STAR climate zone finder.

ENERGY STAR zone	U-factor	SHGC
South-Central	0.28 or lower	0.23 or lower
North-Central	0.25 or lower	0.40 or lower
Northern	0.22 or lower	0.17 or higher
Southern	0.32 or lower	0.23 or lower

Across California, in the GlassBase heating and cooling model, replacing a single-pane window with an ENERGY STAR window saves 369 kWh per window per year. Upgrading a double-pane window saves 185 kWh.

In the Northern zone, the SHGC limit is a minimum, not a maximum. ENERGY STAR also lets a window with a slightly higher U-factor qualify if its SHGC is high enough to collect more winter sun. See window energy ratings in the US for the full table.

What matters most for windows in California

In California, most of the modeled saving comes from cooling: 230 kWh of cooling load against 138 kWh of heating load per window per year, for a single-pane to ENERGY STAR upgrade. SHGC measures how much solar heat the window lets in. A lower SHGC means less heat for the air conditioner to remove.

Results vary inside the state; see the city table below.

Modeled savings per window per year across California

One window of 39 × 59 in (1 × 1.5 m), averaged over eight facing directions. Weather: 80 TMY3 weather stations.

Upgrade	Heating saved, kWh/yr	Cooling saved, kWh/yr	Total, kWh/yr	Natural gas saved, therms/yr gas furnace	Heat pump + AC, $/yr	Gas furnace + AC, $/yr
Single-pane → double-pane	130	54	184	5.2	20	18
Single-pane → ENERGY STAR (each location's zone)	138	230	369	5.6	44	42
Double-pane → ENERGY STAR (each location's zone)	8	176	185	0.3	24	24

Dollar figures use California average prices, not your utility's rate. Electricity $0.3254/kWh: California residential average, 2025. Source: U.S. EIA, Electric Power Monthly, Table 5.6.B, residential sector, year-to-date through December 2025, retrieved 2026-10-06. Natural gas $2.15/therm: California residential average, 2025. Source: U.S. EIA, Natural Gas Prices: price delivered to residential consumers, and heat content of natural gas delivered to consumers, 2025, retrieved 2026-10-06. Heat pump COP 3.2, air conditioner COP 2.5, gas furnace efficiency 85%.

The single-pane and double-pane windows use values from the calculator's reference-window table. In California, each location uses the limits of its own ENERGY STAR zone (South-Central, North-Central, Northern, Southern). kWh here measures heat, not electricity on a bill. Air leakage and the rest of the house are not modeled. Model version tmy3-hourly-iso13790/f4822a26309b, data run October 12, 2026. How the model works.

Cities in California

Modeled savings per window per year in California cities with a GlassBase page.

City	ENERGY STAR zone	Total, kWh/yr single-pane → ENERGY STAR	Total, kWh/yr double-pane → ENERGY STAR
Los Angeles	South-Central	223	108
San Diego	South-Central	192	84
San Jose	South-Central	275	106
Sacramento	South-Central	513	264
San Francisco	South-Central	179	27
Fresno	South-Central	602	344
Long Beach	South-Central	273	151
Oakland	South-Central	192	34
Stockton	South-Central	561	302
Riverside	South-Central	510	292
Anaheim	South-Central	321	180
Santa Ana	South-Central	167	73
Irvine	South-Central	167	73
Chula Vista	South-Central	171	49
Modesto	South-Central	533	298
Fremont	South-Central	241	82
Oxnard	South-Central	134	18
Moreno Valley	South-Central	609	354
Santa Rosa	South-Central	401	158
Oceanside	South-Central	189	63
Salinas	South-Central	204	33
Hayward	South-Central	224	73
Escondido	South-Central	153	45
Rancho Cucamonga	South-Central	496	279
El Cajon	South-Central	185	72
Garden Grove	South-Central	284	155
Glendale	South-Central	413	242
Roseville	North-Central	485	228
Victorville	South-Central	513	286
Santa Maria	South-Central	233	47
Murrieta	South-Central	454	243
Fullerton	South-Central	326	185
Tracy	South-Central	492	244
Santa Clara	South-Central	275	106
Berkeley	South-Central	192	34
Concord	South-Central	410	192
Fairfield	South-Central	447	209
Vista	South-Central	107	14
Ventura	South-Central	135	23
Redding	South-Central	598	324
Costa Mesa	South-Central	167	73
Hesperia	South-Central	472	269
Redwood City	South-Central	219	61
San Leandro	South-Central	210	56
Indio	South-Central	900	565
Santa Monica	South-Central	133	41
Walnut Creek	South-Central	410	192
San Ramon	South-Central	328	131
Mountain View	South-Central	241	79
Upland	South-Central	503	283
Camarillo	South-Central	242	89
Covina	South-Central	326	185
Davis	South-Central	535	278
Folsom	South-Central	507	260
Thousand Oaks	South-Central	242	89
Bellflower	South-Central	273	151
Rancho Cordova	South-Central	507	260
Campbell	South-Central	275	106
Newbury Park	South-Central	242	89
North Highlands	South-Central	535	278
Orangevale	South-Central	507	260
San Carlos	South-Central	179	27
Belmont	South-Central	179	27
Laguna Beach	South-Central	167	73
Belvedere Tiburon	South-Central	179	27

Payback of each upgrade in California

Calculate savings for your ZIP code

Compare states: window energy savings by state.

Frequently asked questions

Which ENERGY STAR climate zone is my home in?

California has 4 zones: South-Central, North-Central, Northern, Southern. ENERGY STAR assigns them by county, and in some places by ZIP code. The ENERGY STAR climate zone finder gives the zone for an address.

How much can new windows save in California?

Across California, for a single-pane to ENERGY STAR upgrade, the GlassBase heating and cooling model saves 369 kWh per window per year. At California's 2025 average prices from the U.S. Energy Information Administration (EIA), the single-pane to ENERGY STAR upgrade is worth about $44 per window per year with a heat pump. Results differ from place to place; use the calculator for your ZIP code.

Is the ENERGY STAR zone the same as the building code climate zone?

No. ENERGY STAR uses four zones of its own, assigned by state and county. Building energy codes use the IECC climate zones, a separate map with its own window requirements. A window can meet one and not the other, so check both if your project needs a permit.