Thinking About Replacing Your Windows? Don’t Believe the Big Energy Savings Promise!

2012_0713We shared a blog post on Georgia’s sales tax holiday for ENERGY STAR & WaterSense labeled products earlier this week. In that post, we promised to follow-up with some notes on replacing windows because many people are surprised, if not disappointed, to find replacement windows don’t perform as expected. Windows are included in the sales tax holiday which begins today.

Replacement windows are just that – they’re a replacement for, and often an upgrade of, the existing windows in a house. Replacement windows are often sold has having three distinct advantages over existing windows:

  1. Replacement windows look better than your old, worn out windows: Even if your existing windows work fine and you never give them a second thought, the discussion of “curb appeal” is popular. Since windows can significantly impact the appearance of your house, they’re often drawn into the discussion. This is a great place to start a sales pitch because you don’t need any technical knowledge to agree they look nice. So, the sales person has you nodding in agreement when he|she introduces the following points…
  2. Replacement windows are more functional: Amenities like tilt-in sashes make it easy to access the outside face of the windows so you can clean and maintain them from inside your house – you don’t have to climb a ladder! For many people, this means the windows are safer and we imagine that we’ll actually clean and maintain them even though few people seem to do that regularly.
  3. Replacement windows are more energy efficient than your existing windows: They use the latest designs, materials, glass coatings and fabrication technologies to achieve a level of performance that your existing windows cannot.

Even if those all sound like compelling reasons to replace the windows in your house, please be careful about the weight you give to the last point. Some sales people talk in round numbers about the possible energy savings from replacement windows, suggesting that you’ll save 20% or 30% on your energy bills. That’s rarely the case though the reason puzzles many people.

In Georgia’s climate, controlling humidity by air sealing is the key to success when it comes to energy efficiency. Houses that don’t have tight exteriors allow air to flow through cracks and leaks in the exterior walls. In our climate, that air flow brings high outdoor humidity into our houses in the summer months. We waste energy by air conditioning our houses to try and reduce the indoor humidity so we’ll feel more comfortable: an indoor air temperature of 75 degrees feels comfortable at an indoor humidity of 60% though it’s noticeably warmer at the same temperature when the indoor humidity is 70%.

In the winter months, when the outdoor humidity is low, we lose energy as our indoor humidity and heated air escapes through the same cracks and leaks that cost us during the summer months. Maintaining an indoor humidity of at least 40% will help you feel warmer than you will at lower humidity levels even if the temperature is constant. It’s just the opposite of what happens in the summer months.

So, rather than focusing on our windows as the reason for poor energy performance, we should focus on insulating and sealing our houses so we don’t have unintended air flow. We should manage the flow of air between the exterior and interior with a ventilation system so that we get fresh air while conserving energy. If you’d like to figure out whether your house has air leaks, please consider an energy audit. It’s possible to pressurize your house through a simple test (called a “blower door test”) to find your leaks.

As long as your existing windows don’t allow air to flow through cracks and leaks in and around the windows, you’ll probably not get anywhere close to a 30% energy savings by replacing them. If you are concerned about energy loss through your windows, storm windows added to your existing windows will probably be much more effective for the amount of money invested. (Your architect or sustainable building consultant can help you study your specific situation to give you better direction than “probably”.)

Ultimately, you’ll consider more than one factor in your decision about whether to replace your windows: appearance and function are also important. Even though they’re more difficult to measure than energy efficiency, they’re probably more legitimate reasons to replace your windows than energy efficiency.

Photo by mahalie used under a creative commons license.

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One Response to Thinking About Replacing Your Windows? Don’t Believe the Big Energy Savings Promise!

  1. Pingback: FTC Warns Window Manufacturers About Unsubstantiated Energy Efficiency Claims | Ryan Taylor Architects LLC

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