When retrofitting buildings for efficiency, replacing windows can be a great place to start. Windows can comprise up to 25 percent of a property’s exterior wall area and can account for up to 50 percent of a property’s heating and cooling demand (1). However, replacing otherwise functioning windows only for the sake of increased efficiency is generally not cost effective. Windows tend to be expensive, and the cost savings due to increased efficiency will usually not recoup your initial investment in a satisfactory time period.

However, if your property is already in need of window replacement for any reason—aesthetics, old windows that leak air, security concerns—MUP strongly suggests investing in ENERGY STAR windows, which offer significant energy savings through state-of-the-art air sealing and UV protection.

Windows: How to Read Efficiency Ratings

Window technology has advanced significantly over the years, and ENERGY STAR windows not only take advantage of these improvements, but also exceed California’s Title-24 energy code.

U-Factor—determined in part by frame construction and number of glass panes—measures how well a window manages heat transfer between the exterior and interior spaces, which helps reduce demand for heating and cooling. The lower the number, the better a product is at keeping conditioned air inside.

Solar heat gain coefficient (SHGC) measures how well a product filters UV rays (heat) entering the interior space, especially important during hot summer months when cooling is in demand. The lower the number, the less you’ll spend on cooling. Note that in climate zones 1, 3, and 5, which are home to colder-weather cities such as San Francisco or Eureka, you may want windows that feature a higher SHGC rating (less heat filtering) to take advantage of daylight heating during cold periods.

Windows Title 24

Cost Savings and Benefits

ENERGY STAR rated windows save, on average, $126-$465 a year when replacing single-pane windows and $27-$197 when replacing double-pane windows(2). In addition to energy and cost savings, upgrading with state-of-the-art ENERGY STAR windows can provide your property and its residents additional benefits:

  • Increased comfort: well-installed, high performance windows significantly reduce drafts, which will keep residents happy and comfortable in their units.
  • Longer life of building materials: high performance windows reduce UV ray transmission, which reduces sun damage to floors, carpets, furniture, and other interior fixtures.
  • Decreased risk of rot and mold: old, inefficient windows can allow excess leakage of water into the building, which can lead to rot and mold.

How MUP can Help

As previously mentioned, MUP does not generally consider replacing windows simply to reduce energy spending cost-effective. However, if your property is already considering replacing windows, MUP can help you determine which mix of windows and other energy efficient retrofits could make the entire project cost effective, thus increasing your potential future net operating revenue.