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Energy Efficient Windows And Features
Energy efficient windows and the features that go into making them ought be an important factor when shopping for replacement windows. Generally speaking, energy efficienct windows help lower your monthly heating and cooling bills, which helps you save hard earned money. Additionally, increased energy efficiency helps conserve on overall usage, which is helpful to the environment (which is never a bad thing). Perhaps most importantly, a window upgrade makes for a more comfortable home, especially during hot summers and cold winters. All good things - except for the price tag of course.
My Take: Replacing your old windows for more energy efficient windows can be a good investment. (Although not if you are planning to move in the next decade - see our article on roi on new windows for a full breakdown on actual return on invest.) There are a wide selection of windows brands and series to suit the climate you live in and, most importantly, your budget. We will make some specific recommendations at each price point to help you in our search for the right window for your situation.
(Always Get 3 to 4 Local Price Quotes)
Dane - Site Editor - Page Last Updated: June 3, 2025
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"The IGU, along with the frame itself, are the two biggest factors that help reduce the loss of heat through the window during the winter and reduce heat entering the home during summer."
Insulated Glass Unit
A window's insulated glass unit (commonly abbreviated as IGU) is one of the most important elements in ensuring energy efficient windows. The IGU contains both panes of glass (or all three panes with triple pane windows), proper spacing between each pane, a "gas fill" between the panes, and an exterior mini-frame. This insulated glass unit is completely insulated and sealed, as the name would indicate. While the energy efficiency goes up based on the number of panes, so too does the cost. However, most homeowners can enjoy a comfortable temperature and proper energy efficiency with a double quality double pane glass.
Energy Efficient Windows: Gas Fills
Adding gas fills between the glass panes will also increase a window's overall energy efficiency. Argon gas fills are the most popular option for double pane windows, while krypton gas is most often used in triple pane windows. Specifically, gas fills reduce that heat/cold transfer from one window pane to the other. Many IGUs include gas fills, but often this is a simple upgrade (think $25 to $45 per window). Generally speaking, adding gas fills will make a window 10% more energy efficient. However, any seal failure in the IGU during the life of the window means you lose the gas fill and its affects.
Low-e Glass
Low-e glass is a big part of energy efficient windows. In the past, window manufacturers used clear glass that did not contain any exterior coating(s). Clear glass allows both UV rays and the corresponding heat/cold to easily pass through the pane of glass. Low-e window glass contains one or more coatings that allow light to flow through, but reflects (some amount of) heat and cold. The particular low-e coating(s) are designed according to your local climate to ensure you receive the maximum benefit (and most energy efficient outcome).
Many window companies have clever names for the different replacement window glass packages that they offer. However, most companies name the glass packages they offer like this: Low-e, Low-e 2, and Low-e 3. These typically corresponds to the number of layers or coating applied to the glass. A knowledgeable window installer or contractor should be able to suggest the correct low-e coating for your local climate. One note: the higher the low-e option, you go with, the more tinting a glass can have. Most homeowners can go with a standard low-e coating to provide good energy efficiency without making your windows too dark.
Low-e glass will often add $50 per window to the cost. Low-e 2 glass will often add $75 to the per window cost. Finally, low-e 3 glass will often add $125 per window to the cost. However, the actual cost that a company charges is often arbitrary so always ask about the cost of a low-e glass upgrade. While low-e glass is usually seen as a positive, check out the disadvantages of low-e glass here so you have all the information prior to your purchase.
"Replacing old single pane aluminum windows with energy efficient units should reduce energy bills and create a more comfortable home environment. This is a welcome change during the extremely hot and cold months of the year."
Spacer Systems
Window spacers sit between the two (or three) window panes and help to reduce the amount of heat transfer. In the past, companies used aluminum spacers that were less than ideal because metal conducts both heat and cold. (In fact, this is the primary reason that so many aluminum windows gets such poor performance numbers.) Today. manufacturers use insulated or non metallic spacers. These spacers are made out of silicone foam, vinyl, rubber and (a tiny amount of) steel. The result is a more energy efficient window within the insulated glass unit.
Energy Efficient Windows: Tinted Glass
To be honest, this one is really more of a footnote than anything. Not many manufacturers put a tint on their home windows. The reason is that most homeowners want to see the outside world as clear as possible. What is also true is that low-e glass is slightly darker than clear glass. In fact, every coating that goes on a low-e glass will darken the window a tad. Some homeowners do like the tinting option as a way to reduce the amount of heat that enters a window. Typically, this would be used sparingly and only on those windows that received lots of sun - usually south facing windows.
Regardless of how infrequently they are used, tinted windows do assist with some energy efficiency. These days tinting isn't very noticeable, unlike years ago when they were dark windows, which means you can include them on your home and they will look the same as the other windows in the area, just offering more of an energy advantage.
Homeowner Review Section
Below are our energy efficient windows reviews, project pricing, consumer accolades and/or complaints.
Dane - Site Editor
Best Energy Efficient Vinyl Windows
I have large windows on new build 6’x6’ wonder will vinyl casement be fine? Fiberglass quote I get is double than vinyl from pella. Learned here pella not great. Who makes best vinyl windows then? Also, would you know what the R Value would be for the OKNA 700 Casement Deluxe Package as well as the air filtration rating? I've seen the window stats but I am not sure which window it corresponded too.
Doug - Homeowner - from 2025
[Site Editor's Answer]
Doug, that's a pretty big span, but as long as it's an Okna picture window, I would think you'd be fine. A good installer should be able to tell you whether they think you're going to have an issue, but Okna or Soft-Lite are going to be fine in that scenario. I am happy to send you my list for your consideration. And while I don't know the R value of the window offhand, I do know that it has an air infiltration rating of .02, condensation resistance of 63, U-value of .26, and VT of .38 - all excellent performance numbers.
Dane - Site Editor - from 2025
ProVia vs Okna Windows
Dane, thanks for all your advice. I am going with Provia Endure, compared to Soft Lite and Okna. All 3 quotes were less than $25,000 fully installed, lifetime warranty on windows and the labor, for 24 double hungs and 2 awning windows instead of 2 fixed windows. All double pane, AI is .05, u is .27, schg is .27 and the vt is 54 and CR is 71. The window has the super spacer and kevlar fiberglass reinforcement at the sash and triple weatherstripping. I think these are good enough. Not really looking for the most energy efficient windows because that would require all in triple pane and more costly from each of them.
An engineer said that Soft Lite's balance system was not doing the heavy lifting. Thus, the top sash was failing and was affecting the locking mechanism. Not sure to what extent that is, I did like the look of Soft Lite Imperial Elite. Also they use the intercept and not the super spacer. The OKNA 600 and 800, not crazy about the look of the window. The corners and the outside wrap is very cumbersome. It looks like they didn't finish the product in the mfg process. It looks like they wrapped the entire window in a vinyl sheath.
With Provia, Houston Window Experts said it was a great window, another guy who presented the window showed all the pros and cons, and Jeff from Zen Windows of Cleveland has done the best job selling it to me. I feel confident that I received a fair deal and one of the better windows. You are doing a great service so thank you!
Mark - Homeowner - from 2025
[Site Editor's Answer]
Mark, the ProVia Endure is such a great window and gets very good performance numbers. Good on you for all of your diligence during this process. It's a pain in the @ss, but now you (hopefully) won't have to deal with it for a long long time!
Dane - Site Editor - from 2025
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