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How to Buy Energy-Efficient Windows

Global warming. Water shortages. An ever-growing number of 110+ degree days every summer. It’s never been more important to be a savvy consumer who considers the impact on our environment when shopping. And windows are one area where your choice makes a difference. 

And to add an extra note of delight to the shopping experience, it can be a GREAT opportunity to lower your heating and cooling bills. What’s good for the planet can be good for you, too. 

So, how do you buy energy-efficient windows and make sure you get the best quality at the best price? These five areas make the biggest impact. 

1. Check the ratings

Frames make a huge difference in your window’s energy efficiency, because it drastically impacts the seal of a window. The tighter the seal, the less air leaking in or out of the home. 

Also, since glass takes up most of the surface area of a window, choosing the right glass matters, too. (More on that in a moment.)

Together, window glass and the frame have the largest impact on the total energy efficiency of a window, which is indicated by two specific ratings: U-factor and SHGC. 

You can find the ratings for a specific product on a window cling sticker that comes on the product, or a manufacturer’s website.

This is important, so perhaps instead of relying on a
salesperson’s memory for these ratings, ask for
documentation or pull it up on your cell phone.

So exactly what are you looking for when it comes to the U-factor and SHGC ratings? Heat transfer in and out of the window, or its ability to insulate during the summer and winter.

Energy-efficient window ratings

U-factor ratings indicate the amount of non-solar heat transferred through the window unit during the winter months. It’s looking at how well it’s keeping the furnace-heated warm air inside the home from leaking outside. Lower numbers mean the window is well insulated on a scale from .20 to 1.25, with the lowest number meaning zero transference. 

That’s what you want. 

Documentation should reflect either a NFRC U-factor from the National Fenestration Rating Council, which rates the entire window unit and is preferred, versus a U-factor rating for the glass. 

(Learn more about glass and glazing.)

But the other season—summer—is the toughest one in the Sonoran Desert, given our extreme temperatures— and SHGC ratings indicate just how much solar heat comes inside the home through the window. Arguably the more important score in Phoenix, SHGC scores range from 0.0 to 1.0,  reflecting the percentage of heat transmitted into your home, and you’ll want to look for ratings on the low end of that scale.  

2. Select frame materials wisely. 

Materials used to create the window frame can have a powerful impact on the overall energy efficiency of a window, since each is manufactured differently, and has its own individual ability to transmit heat and cold. 

Let’s take a closer look at the five most common materials used for window frames, which we’ve ranked from most energy efficient to least.

  • Fiberglass frames are a whopping eight times stronger than vinyl. Made of glass fibers and incredibly strong, a fiberglass frame will hold its shape perfectly over time without warping, expanding or contracting. The result is a reliable window that keeps its seal, structural integrity and beautiful aesthetic for as long as 30+ years, an investment that will pay off in reduced electricity bills for decades. It’s our top choice for durability and longevity, as well as energy efficiency. 
  • What window frame materials are the most energy efficient?Composite frames are made from a blend of wood fiber and polymers. For example, Andersen® Windows created their own proprietary formula, Fibrex®, which is a step up from vinyl frames. Not only is it one of the most energy-efficient frame materials on the market–second only to fiberglass–it contributes to their sustainability efforts by recycling wood waste from their manufacturing process. Composites are stable materials with the same or better structural and insulating features compared to wood. Unlike wood, however, you don’t have to worry about decay or water damage. 
  • Vinyl frames are made of polyvinyl chloride (PVC) with ultraviolet light (UV) stabilizers to reflect sunlight and protect the material so it lasts longer. Good quality vinyl window frames never require painting, have excellent moisture and insect resistance, and are the most popular, budget-friendly option in America, according to the U.S. Department of Energy. Vinyl is non-conductive, making it very energy efficient; plus, a vinyl window with multiple chambers for air insulation is more efficient than a comparable window with fewer chambers. Quality is important, though, so it’s important to choose a high quality frame that won’t bend or flex. Soft vinyl quickly warps and shrinks in the Arizona sun, especially when the resin includes recycled vinyl. 

(Learn more about shopping for vinyl windows.)

  • Wood frames are paintable, attractive and insulate fairly well. Unfortunately, wood expands and contracts with changes to weather and humidity, which impacts energy efficiency and insulation. It’s also more prone to rot, termites and water damage than other materials, and requires quite a bit of maintenance. If you’re interested in wood, be sure to purchase wood windows that have aluminum-clad exteriors for improved durability and protection.  
  • Aluminum frames are strong and light, however, they are the least energy efficient option because of how they conduct heat. Some manufacturers still sell aluminum windows in some states with moderate climates, but they’re not practical for Arizona weather because of their extremely high U-factor ratings. Thermally broken aluminum windows can be a good option if you want strength, more efficiency, and a wider  variety of color choices; however, they are still less energy efficient than any other material option. 

3. Choose the Right Glass

It can be challenging to produce windows that allow maximum light into the home, yet still block harmful UV rays and solar heat. Since glass makes up the largest component of the window, it’s the most critical element for managing heat and saving money on your utility bills, and choosing the right glass is one of the smartest ways to be more energy efficient. 

  • Look for multiple panes, such as dual-pane glass, which is far more efficient than the outdated single-pane glass found in many older homes. It’s ideal for desert climates like ours. Should you consider triple-pane glass? It has a high U-factor that’s perfect for colder climates like Northern Arizona, but we don’t recommend it for hot climates. It makes a miniscule (if any) difference in air conditioning bills that takes decades to recoup your investment. Instead, consider investing in other upgrades while sticking with double-pane glass.
  • Three or four low-E coatings are optimal. Low-E glass has a thin metal coating layered between the panes of glass to block heat and harmful UV rays from entering your home. Thinner than a human hair, it also reflects interior temperatures back inside the home during the winter months. This is one of your best allies for combatting extremely hot weather, and maximizing energy efficiency. Most windows include double coatings (low-E2) as standard, but upgrading to a low-E3 or low-E4 coating is worth every penny. 
  • Gas fills are a must; it insulates far better than air. Argon gas is the most common filler. It’s heavier than air, non-toxic and infused into the air space of your glass between each pane. In combination with low-E coatings, this superior insulation creates a barrier that reduces heat transfer in the winter months.

What is the best glass for energy-efficient windows?DunRite Windows & Doors includes an argon upgrade at no extra charge.
It’s critical for any home in the Phoenix area.

4. Select a Window Style with a Tight Air Seal

How tightly your windows are sealed to the frame is an essential consideration when you’re aiming for maximum energy-efficiency. Windows come in multiple types of operating styles: Double-hung, casements and awnings, and sliding–but each one seals slightly differently.

  • A double-hung window slides the bottom portion of the window up to open and down to close.
  • A casement window opens on the side and hinges left or right, and typically closes with a handle or hand crank. 
  • An awning window is hinged at the top and swings outward from the bottom to let air in.
  • A sliding window is similar to double-hung windows except the sashes move to the right and left, instead of up and down.

Besides the obvious differences, choosing how the window operates can make a big difference with how the window seals. According to one manufacturer, casements and awnings all swing outward and when locked, they are pulled tightly against their weatherstripping. From an energy-efficiency standpoint, these compression seals give those windows a distinct advantage over windows that slide. 

So, if you’re looking for unique, energy-saving options for your home, consider incorporating casement windows if the size of the openings allow. 

5. Partner with a Reputable Windows Company

Ultimately, you can buy the best energy-efficient windows available, but if they’re installed incorrectly, you won’t realize the savings. 

Proper installation is absolutely essential.

Look for a reputable windows company with a strong reputation, a solid Better Business Bureau rating and no issues with the Arizona Registrar of Contractors. It’s also important to obtain multiple quotes, since pricing can vary widely–even for the same product line. 

Ready to explore energy-efficient window options and pricing? We provide service to homeowners in the Phoenix metro area. Just reach out to us at (602) 456-2227, or via our website form to schedule an estimate! 

We also offer this free ebook download on smart shopping tips for replacement windows.

Updated June 22, 2023

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Please note that we install replacement windows and doors, but we don’t repair them or replace broken glass. Three-item minimum purchase, some doors excluded. Refer to our FAQ and warranties page for details.


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