Question

Are (non-opening) picture windows more energy efficient than windows that open? If so, what should I look for?

Asked by Wendy Smith
Camp Hill, PA

I currently have old wooden double-hung windows with after-market storm windows. I never open these windows since I get excellent cross-ventilation through the doors. The many layers of paint on the windows make them nearly impossible to open and clean. So, I'm considering replacing them with fixed picture windows which will make it easier to keep clean them, will let in more natural light, and will provide a better view. What are your thoughts? Thanks!

Answer

Richard Williams

Answered by Richard Williams

Encinitas, CA

Arthaus, LLC

November 13, 2012

Dear Wendy:

This is a great question that is fairly simple to answer. Funny enough, about 6-years ago I changed out the windows in my 1948 San Diego Beach Bungalow because I had the same problem in that many of the double hung windows (all original) would not open anymore.

There is a slight difference between the "performance" available for operable versus fixed windows, but not as much as you would think. When I say performance, there are generally two factors that come into play regarding how much energy efficiency windows provide.

  • U-Value
  • Solar Heat Gain Coefficient

U-Value

The first and usually most important factor is called U-Value. In simple terms, the U-Value reflects the ability of a window to resist thermal heat transfer

This means, for example, how much heat leaves your home through a window in winter. 

  • Now, when I talk about windows, I don't just mean the glass (glazing.) The frame comes into play, and in most cases most of the thermal loss actually takes place in the frames of windows.
  • So, as I'm hoping you can understand, metal windows are not as energy efficient as wood windows.
  • The U-Value takes into account the thermal transfer of heat through both the glazing and the frame of a window.

Solar Heat Gain Coefficient

The second factor is called the Solar Heat Gain Coefficient (SHGC.)

This, in simple terms, represents a window's ability to resist the heat generated by sunlight coming through a window. The SHGC is a tricky animal, because sometimes you would like to have the sun coming in your windows and heating your home, and other times not.

  • This is where properly sized and placed overhangs come into play, as they can allow sunlight to come through a window in winter and then shade a window in summer.
  • But, don't worry yourself too much about SHGC because you are probably not going to have much flexibility in choosing both a window with a good U-Value as well as selecting for appropriate SHGC.

Sorry, I know it's complex. I take it back when I said it was fairly simple to answer your question! Really though, don't worry too much about SHGC because windows with high-performance U-Factors generally perform well too with SHGC.

Low-E windows

You will have likely heard of Low-E windows though, and these resist solar heat gain more than windows without Low-E.

You should probably talk to window companies about recommendations for your home, as you might want to have Low-E on some windows of your home and not on others. 

Choosing a new window

So, what to look for when browsing window performance data? One important thing for you to know is the lower the U-Factor the better, and the lower the SHGC the more resistant a window is to solar heat gain.

I like to say that you should look for windows with U-Factors of no more than 0.32, or better yet 0.30 or less. 

Fixed versus operable

When you look at the manufacturers' websites, you will notice that for a line of windows you might see that there is a surprisingly small difference in the U-Factors of fixed versus operable windows. So, I wouldn't worry about window performance being a deciding factor in your choice of operable versus fixed.

What WILL be a factor is that you can save money by going with all fixed windows, you will have better views, it will be easier to clean them, and you won't have screens to clean or have hindering your view. And, yes, even with the small difference in performance ratings of the windows you will find that you will have greater energy efficiency in your home, especially when you consider you will have less air leakage with fixed windows (if they are installed correctly!)

The only problem that I can see with going all-fixed for your windows is when (if) if comes to selling your home. it might be a show-stopper for some buyers that they cannot open the windows. Thought I had better throw that in as food for thought.

Hope that I helped out a little bit! Good luck.  

 

For more information:

Read "What are my best options when purchasing and installing new windows? Our floor to ceiling windows are old and need to be replaced." a Q&A answered by Michael Holcomb.

Tagged In: energy efficient window, windows

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