Solar Heat Gain Coefficient (SHGC): What It Is and Why It Matters in Window Replacement in San Diego

This blog post is for the more science-minded and math-minded individuals out there. You know who you are! We wanted to get into one of the metrics for comparing the energy efficiency of various replacement windows on the market: solar heat gain coefficient (SHGC).

SHGC is a standardized rating in the window replacement industry that allows us to compare “apples to apples” when it comes to a window’s insulating properties. This rating will tell you how good a window unit is at keeping solar heat from entering your home. SHGC ratings are determined by the National Fenestration Ratings Council (NFRC), which is an independent, third-party organization that evaluates just about every replacement window on the market, including those sold in San Diego.

How Is SHGC Calculated?

A window’s SHGC rating involves a fairly simple calculation. It is the solar heat entering a room, divided by the total solar heat incident on the glass. So, for example if 300 W of solar heat falls on the glass, and 150 W actually enters the room, the SHCG would be 0.50 (150 W / 300 W = 0.50).

In warm climates like San Diego, replacement windows with a low SHGC rating is preferable. As you shop for windows, look for products with a SHGC rating of around 0.25.

Where Do You Find SHGC Ratings?

If you go to a home improvement store that sells replacement windows in San Diego, or a replacement window showroom, the windows they sell will likely have stickers on them with the NFRC’s ratings on them. This sticker will include the window’s SHGC rating (as well as a few other ratings). If you don’t see the sticker, ask a window replacement salesperson to provide you with the SHGC rating. They should be able to easily provide you with this information.

What Contributes to a Low SHGC Rating?

There are several factors that can contribute to a low SHGC rating in windows. First of all, you could opt for windows that are tinted. However, most of the homeowners in San Diego that we work with for window replacement want their windows to be as transparent as possible so they let in a good amount of natural light. In that case, you want to look for windows with other insulating technology built into them. For the lowest SHGC rating, you could have Argon gas inserted between the two panes of glass in your replacement windows. This dense gas will help prevent warm air from passing through your glass panes. If you were buying our most recommended brand of windows (Anlin), we would also advise you to upgrade your glass package from the standard package to the SunMatrix package, which includes four layers of Low-E coating (instead of three layers in the standard glass package).

We should note, however, that the glass package that comes standard with Anlin windows is quite good. There is no need to upgrade unless you want the absolute lowest SHGC rating possible.

There is one caveat to keep in mind as you’re comparing SHGC ratings: a window will only achieve the stated rating if the windows are properly installed—and that’s a big “if.”  Some companies that do window replacement in San Diego use subcontractors for installation, who may not be trained specifically in window replacement. At BM Windows, we only use our own team of highly trained installers for every project.

We would love to tell you more about the windows we sell for San Diego homes and about window replacement in general! Contact our office to schedule a free, in-home consultation.