Given all of the incredibly technological advancements within the home improvement industry, it is an incredibly exciting time to be in the market for new windows. Long gone are the days of windows existing to purely to block the elements from entering a home. Advancements in window technology allow homeowners to lower heating and cooling costs and significantly increase comfort as well. That being said, shopping for new windows can be quite daunting. Stickers and fliers on the windows mentioning things like “window U-value” and “SHGC rating” could be a bit intimidating for folks not sure which window is right for their home (or could even be interpreted as marketing nonsense). Today we are going to lift the veil off of some of these terms to help inform your next window purchase.


One of the most important ratings to pay attention to when looking for new windows is the glasses U-Value. A window’s U-Value, also described as U-Factor, measures the rate the window transfers non-solar heat. In short, it provides a measurable indication of the quality of insulation the window provides. The window U-rating is reflected as a number between 0.20 and 1.20. The lower the U-Value means the glass will transfer less heat, meaning your home will be better insulated. In general, finding glass with the lowest U-rating is optimal in that it will help homeowners better utilize heating.

Solar Heat Gain Coefficient (SHGC)

The Solar Heat Gain Coefficient (or SHGC) rating is another incredibly important rating to pay attention to. The SHGC rating reflects how much solar heat gets inside the home once it has reached the glass. The SHGC rating is measured between 0 and 1, with lower SHGC ratings meaning the glass allows less solar heat from entering the home. The SHGC and U-ratings share an interesting relationship in that they share a relative correlation. Windows with higher SHGC ratings will have higher U-ratings as well, meaning people whom a looking to enjoy some natural heating will have to do so at the expense of insulation value.

What Ratings Are Right For Me?

To make the most informed decision when shopping for new windows, one must take their area’s climate and personal preferences into account. For example the greater Bay Area features several unique microclimates, with coastal communities like San Francisco, Oakland, Berkeley being cooler on average compared to cites inland like Walnut Creek, Concord, Pleasanton, and Livermore. For premier energy performance in a majority of Bay Area communities, looking for a window with a U-Factor of 0.25 or less is crucial. Those living in the Bay Area’s cooler, foggier areas, like San Francisco’s Ocean Beach, and have seen high heating bills the past should look for the lowest U-Factor rating possible to help lower those costs.

When it comes to an optimal SHGC rating, again you will want to look for a rating of 0.25 or less for efficient energy performance and lower A/C costs. Although for people that like their home on the warmer side should choose a SHGC rating between 0.35-0.60 to allow natural solar heat in. Inland communities and neighborhoods that generally feature minimal shading and higher average temperatures will especially benefit from the lowest possible SHGC ratings.

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