Are Double-Pane Windows Worth It in Fullerton, California? Savings and Payback
Data updated October 12, 2026.
In the GlassBase heating and cooling model, replacing a single-pane window with a double-pane window in Fullerton, California saves 141 kWh per window per year: 93 kWh of heating load and 48 kWh of cooling load. At 2025 average prices in California from the U.S. Energy Information Administration (EIA), that is worth about $16 a year with a heat pump and air conditioner, or $14 with a gas furnace and air conditioner.
Simple payback in years = installed cost per window ÷ yearly savings per window. So if your quote is $157 per window, payback with a heat pump is about 10 years.
Payback for your quote
If you are replacing the windows anyway, enter only the extra cost of the more efficient window over the one you would buy otherwise.
Yearly savings and payback per window in Fullerton, CA
Dollars saved per window per year, and the highest installed cost per window that energy savings pay back within 10, 20, 30 years.
| Heating and cooling | Saved per year | Pays back in 10 years at a cost up to | Pays back in 20 years at a cost up to | Pays back in 30 years at a cost up to |
|---|---|---|---|---|
| Heat pump + AC | $16 | $157 | $314 | $471 |
| Gas furnace + AC | $14 | $143 | $286 | $428 |
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%.
Energy saved per window per year in Fullerton, CA
One window of 39 × 59 in (1 × 1.5 m), averaged over eight facing directions. Weather: the nearest TMY3 weather station.
| Upgrade | Heating saved, kWh/yr | Cooling saved, kWh/yr | Total, kWh/yr | Natural gas saved, therms/yr gas furnace |
|---|---|---|---|---|
| Single-pane → double-pane | 93 | 48 | 141 | 3.8 |
Simple payback leaves out changes in energy prices, interest, rebates, tax credits and maintenance. The single-pane and double-pane windows use values from the calculator's reference-window table; the ENERGY STAR window is at the South-Central zone limits. 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.
Calculate savings for your own windows
Other upgrades: Single-pane to ENERGY STAR: savings and payback in Fullerton · Double-pane to ENERGY STAR: savings and payback in Fullerton
ENERGY STAR limits and all upgrades: U-factor and SHGC for Fullerton, CA. Compare states: window energy savings by state. All of California: payback across California. Before you buy: is it worth replacing windows for energy savings?
Frequently asked questions
How is the payback period calculated?
Simple payback is the installed cost of one window divided by the money it saves on energy each year. In Fullerton, CA, the model puts that yearly saving at $16 with a heat pump and $14 with a gas furnace. The calculation leaves out energy-price changes, interest, rebates and tax credits.
Why does this page not show a window price?
Window prices depend on the product, the size, the installer and the job, and GlassBase has no published source for them. Enter the price from your own quote to get the payback.
Will my windows save this much?
Not necessarily. The figures are for one window of 39 × 59 in (1 × 1.5 m), averaged over eight facing directions, in a typical weather year. Your result depends on the size and facing of each window, shading, your current windows and the ones you buy. The calculator takes these inputs for your ZIP code.