How to Read a Window Quote in California: Title 24, Low-E, U-Factor and SHGC Explained

Why the acronyms matter

A window quote from any reputable Bay Area installer will list a frame series, a glass package and a set of performance numbers. Homeowners understandably skip to the total. But two quotes with similar totals can describe very different windows, and the difference lives in those numbers. This article explains them in plain language, from the perspective of a crew that installs Anlin, Milgard and Andersen windows every week.

U-factor: how well the window holds heat in

The U-factor measures how much heat passes through the entire window, frame and glass together. Lower is better. A single-pane aluminum window from the 1970s, which is what we remove from most Tri-Valley homes, has a U-factor several times higher than a modern dual-pane vinyl window. In practical terms, that is the difference between a bedroom that is cold at the glass on a January night and one that is not.

Frame material affects the U-factor almost as much as the glass does. Aluminum conducts heat readily, which is why old aluminum windows sweat with condensation in winter. Vinyl, fiberglass and composite frames are far better insulators, and wood is good too.

SHGC: how much sun comes through

The solar heat gain coefficient, written SHGC, measures how much of the sun's heat the glass lets into the room. It is a number between 0 and 1; lower means less heat. For an inland Bay Area home, in San Ramon, Dublin, Pleasanton, Livermore or Walnut Creek, where summer afternoons are hot and west-facing rooms overheat, a low SHGC is what makes new windows feel like air conditioning. Closer to the bay and in San Francisco, where summers are mild, a somewhat higher SHGC can be a benefit because it lets in free winter heat.

Good installers tune SHGC to the house and sometimes to the elevation: a lower SHGC on the west and south walls, a more moderate one on the north side. Ask whether the glass package on your quote is the same on every window and why.

Low-E: the coating that does the work

Low-E stands for low emissivity. It is an invisible metallic coating on the glass that reflects heat while letting light through, and it is the single most important upgrade in modern window glass. Nearly every window we install has it. The differences between manufacturers come down to how many layers of coating are used and how they are tuned. Anlin, Milgard and Andersen each offer more than one Low-E option, and the right one for a Danville house is not necessarily the right one for a house in the Outer Sunset.

A Low-E coating also blocks most ultraviolet light, which is what fades hardwood floors, rugs and upholstery. Homeowners rarely buy windows for this reason and often mention it afterward as the thing they noticed first.

Argon, spacers and dual vs. triple pane

Between the two panes of a dual-pane window is a sealed space that is normally filled with argon, a dense inert gas that slows heat transfer compared to plain air. The spacer that holds the two panes apart matters too: a "warm-edge" spacer reduces the cold line you can feel at the edge of cheaper glass units and helps the seal last.

Triple-pane glass exists and is standard in cold climates. In the Bay Area it is rarely worth the added cost and weight; a well-specified dual-pane Low-E unit meets code comfortably and performs well here. If a quote pushes triple-pane hard for a Tri-Valley home, ask what problem it is solving.

NFRC label: where the numbers come from

Every new window arrives with a label from the National Fenestration Rating Council, a temporary sticker on the glass with the U-factor, SHGC, visible transmittance and air leakage ratings for that exact window. These are independently certified numbers, not marketing. Your installer needs them for the permit, and you should keep one from the job for your records. If a quote lists performance numbers, they should match what shows up on the NFRC labels at delivery.

Title 24: what California requires

Title 24 is California's building energy code, and it applies to replacement windows, not only to new construction. Under the prescriptive path that most residential window replacements follow, every new window must meet a maximum U-factor of 0.30 and a maximum SHGC of 0.23. Those are not aspirational numbers; windows that do not meet them cannot be used on a permitted replacement in California.

The good news is that the standard Low-E glass packages from Anlin, Milgard and Andersen meet these values, and many beat them. The practical consequence for you is that any licensed installer's quote should already comply, and the permit inspector will check the NFRC labels against the requirement. If a quote is unusually cheap and does not list U-factor and SHGC, ask.

Egress and safety glass

Two more code items appear on a careful quote. Bedroom windows must meet egress requirements, which define a minimum clear opening for escape in a fire and a maximum sill height from the floor. Changing a window style can change the clear opening, so we check this on every bedroom. Tempered safety glass is required in certain locations, including windows close to doors, windows near tubs and showers, and large panes close to the floor. Quotes that include tempered glass where it is required will be slightly higher than quotes that overlook it; the inspector will not overlook it.

What to ask before you sign

Ask which frame series and which glass package you are getting, by name, so you can look them up. Ask for the U-factor and SHGC of each window. Ask whether the glass varies by elevation and why. Ask what the installation method is, retrofit or full-frame, for each opening. Ask who pulls the permit. And ask what the warranty covers for the glass, the frame, the hardware and the labor separately, because those are often different periods.

If a quote answers all of those questions without being asked, you are probably talking to the right company.

Frequently asked questions

What U-factor should I look for in the Bay Area? California requires a maximum of 0.30 for replacement windows. Most quality dual-pane Low-E windows from the brands we install come in at or below that figure.

Is a lower SHGC always better? Not always. Inland, in the Tri-Valley and East Bay hills, a low SHGC keeps summer heat out and is usually the right call. Near the coast, where summers are cool, a moderate SHGC lets in useful winter sun. We often specify different glass on different sides of the same house.

Do I need triple-pane windows in California? Rarely. Dual-pane Low-E glass with argon meets Title 24 and performs well in the Bay Area's mild climate. Triple-pane is a cold-climate product.

What is the NFRC label? An independent certification sticker on every new window listing its U-factor, SHGC, visible transmittance and air leakage. The permit inspector uses it to verify Title 24 compliance.

Does Title 24 apply if I only replace one window? Yes. Any replacement window installed under a permit in California must meet the energy code.