How Much Heat Is Lost Through Windows?

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Child looking out window to illustrate window heat loss

Ever thought about how much heat is lost through windows? According to the U.S. Department of Energy, about 30% of a home’s heating energy goes right out the window — literally.

That’s cause for concern everywhere — but especially here in the Pacific Northwest, where “winter” lasts way longer than three months.

Thus, it makes sense to pay attention to energy loss. Specifically, heat loss through windows.

Windows and Heat

Many of us think about how much heat windows allow into our work and living spaces. When it’s sunny and hot outside, it’s nice to have sunlight indoors — but not so much the heat. That’s what makes window tinting such a superb solution to reduce heat in cases like this. Tinting permits light but keeps summer’s heat outside where it belongs.

Conversely, when it’s sunny and cold outside (admittedly a rarity in these parts), it’s nice to still have that sunlight while retaining the warmth that it brings along for the ride. Here again window tinting does the trick — allowing the sun’s warming rays to penetrate the space just enough to not overwhelm the room.

But there are other factors at play when it comes to determining how much heat is lost through windows. If there are cracks or seams — either in the windows themselves or in the frame — then you are probably losing and wasting a lot of heat.

Let’s take a look at how best to prevent this heat loss.

Preventing heat loss

As we’ve written about before, windows are a weak link when it comes to energy efficiency.

“In fact,” we wrote in our “Low-E Window Film vs. Replacement Windows” blog post, “your windows could be letting in so much heat in the summer, and letting out so much heat in the winter that your utility bills could be 30 percent higher than they should be.” reports on a University of Wisconsin estimate showing that “between 12 and 30 percent of your yearly heating bill goes to make up for heat loss through windows.”

The good news: This type of wasted energy can be avoided with proper window treatments. But it’s also crucial to determine where and how heat is escaping through your windows and make changes to those problem areas.


Even after you’ve battened down the hatches, so to speak, and made it so that no hot air is leaking through the windows themselves, you still have the problem of sunlight to deal with.

Consider installing low-emissivity window film. Plain windows allow heat to pass through via radiation. The addition of low-emissivity window film (aka Low-E) improves thermal efficiency by reflecting that radiant infrared energy away from your home. This means light gets in but the heat stays out.

But what about the reverse? As mentioned above, certainly there are times when we want that heat to get in. No problem! Low-E takes care of this, too.

Low-E reduces interior heat loss during the cold months of the year, helping keep your home nice and warm. It also has the benefit of providing extraordinary ultraviolet (UV) protection. In fact, low-emissivity window film blocks up to 99% of UVA and UVB rays. This has the benefit of also protecting your floors, curtains, furniture and other items from getting bleached by the sun — especially in areas of the home that face west and south, where the solar heat gain is often most noticeable.

Pacific Window Tinting

How much energy is lost through windows is determined by a number of factors. And at Pacific Window Tinting, we have the energy-saving solutions you’ve been waiting for. If your energy bills are skyrocketing, it may be time to consider energy-efficient windows to help save you money. And remember: Energy efficiency comes in many different forms: from insulated walls, windows and doors, to EnergyStar heating and cooling systems.

But above and beyond those, window tinting provides a cost-effective way to reduce your energy consumption by allowing just the right amount of heat and light into your home.

Call Pacific Window Tinting today — and make losing heat a thing of the past.