California Energy Consultant Service

Nothing enhances a space quite like a window. Windows allow natural light, make rooms seem bigger, and make properties look more open and inviting. But windows are also large pieces of glass that allow the sun and warmth from outdoors to pass through, which can be a problem here in Northern California, where the heat and sun can be oppressive. That is why it is important to choose windows that may offer you some protection from this excessive heat.

U-Factor is a technical measurement of heat transfer. It is one of the measurements used to determine how much heat should transfer through a window. The technical measurement for U-Factor is complex, but the easiest way to understand U-Factor is that a score of 0 would mean “no heat transfer” and a score of 1+ represents “substantial heat transfer.”

Window technology has changed dramatically over the past several decades. Let’s talk about the U-Factor differences of single pane windows, older double pane windows, and the double pane windows today.

Single Pane Window U-Factor

As with all windows, every brand is different. But single pane windows – which were very common back in the 1960s and prior, and are still found in homes in Fair Oaks, El Dorado Hills, Orangevale, and places with more midcentury modern designs – had substantial heat transfer.

The U-Factor of these single pane windows ranged from 1 to 1.2+. A considerable amount of heat transfer occurred, and still occurs, in homes that used these windows. For reference, if you have PGE as your electricity provider, this could lead to 40% more expensive energy bills every summer.

1980s Double Pane Window U Factor

The 1970s and 1980s saw double pane windows becoming standard. Most new properties were built with double pane windows during this time. Many properties from before the 1980s also switched to double pane windows by around 1990.

The U-Factor during this timeframe varies considerably. The first double pane windows in the early 1980s and late 1970s were air filled, which had a U-Factor of about 0.6 to 1. By the 1990s, the U-Factor decreased all the way to about 0.4 as the space in between the windows switched from an air to a gas. Thus the difference between 1960 single pane windows and 1990 double pane windows was dramatic – about 60% less heat transfer.

Modern Day (2020s) Double Pane Windows

Still, technology has improved even more since then. Today’s double pane windows, which are almost universally filled with argon or krypton gas, has a U-Factor of around 0.25 to 0.3. The improvement is not substantial if your older windows are from the early 2000s or late 1990s, but if you had 1980s double pane windows, that number represents as much as a 40%+ improvement from the windows of the past.

Switching Windows for Energy Efficiency, Style, and Function

There are many reasons that a homeowner may want to change their windows. Older windows lose their aesthetic appeal. Older windows may not be in the style you want (for example, white frames vs black frames). Older windows may have leaks that require professional repair.

But another reason that many homeowners choose to replace their windows is because they need windows that are less energy wasteful – windows that will not transfer as much heat. Switching from single pane windows to double pane windows represent an almost incredible amount of energy savings, and even switching from older double pane windows to newer double pane windows can save a surprising amount of money and make your property more comfortable. Pay attention to the U-Factor, as it may represent a substantial savings on your energy bill and a temperature stable home.