Windows 101: Know What You’re Getting Before You Buy

What To Look For in Buying a Window
Buying a window takes far more research than buying a sofa. That’s because windows are a complex commodity. A window is meant keep you comfortable and dry while offering a nice breeze now and then. At the same time it needs to withstand the harshness of the outside environment while keeping the inside as pleasant as can be. And it needs to do all this as efficiently and as cost effectively as possible. Some windows do this better than others and to some degree, they’re designed that way. They’re made to meet variable budgets and utilize different materials to achieve different goals. So before you choose your next set of windows, spend a bit of time discovering how they’re put together. That way, you’ll make a much better window choice.

The Important Parts Of A Window
Shopping for new or replacement windows without knowing much about the product is sort of like buying a new car without doing any prior research. It’ll roll down the road but it may not meet your needs. You might even end up with a lemon. The same is true for new windows. They’re a bit more complex than you might think. Gaining an understanding of a window’s construction, it’s important parts and how they impact it’s performance is key to making good buying decisions. At a minimum you’ll be better equipped to discuss the topic with window salespeople. Window construction is made up of many individual pieces and components but the parts listed here are the important ones to get familiar with.

Window components include the frame, sash, glass a.k.a “glazing”, and muntins.

The window frame is the part of the window that forms the “foundation” of the entire window structure. It’s also the part of the window that identifies the material the window is made from. In other words, when you hear the term “aluminum window” or “wood window”, those descriptions are based off of the material that the window’s frame is made from. The window frame and the material it’s made from is important because it plays a big role in the window’s cost, performance, and how easy or difficult it is to maintain. See the section below for more information about window frame materials and their pros and cons.

The sash is the movable part of the window. In a casement window it’s the part that swings out. The sashes on a double hung window slide up and down beside each other. The sash is also a “frame” in that it surrounds and retains the glass. That frame is made up of the “stiles” (the vertical parts of the sash frame)

The glazing is just another word for the glass within a window. When window manufacturers refer to “glazing options” they’re talking about the various kinds of glass you can get with your windows. The glazing is important because it, along with the frame, has a lot to do with the overall performance of your window. The type of coatings on the glass as well as how many pieces of glass that are in the window impact how quiet, efficient and easy to clean your windows will be. Single glaze windows use only one piece of glass; double and triple glazed windows use 2 and 3 sheets of glass respectively and are more energy efficient.

Muntins (a.k.a. grilles or grids)
Window muntins are traditionally the framing pieces that support individual panes of glass (these individual panes are also known as “lites” or “lights”). They were necessary on older windows because glass could only be manufactured in small pieces and in order to make larger windows a number of small panes of glass would be joined together using this type of framework. Modern windows can be made with large pieces of glass which don’t need all that support structure. However the look of a window with multiple panes is still desired by many which is why the style is with us today. The key point here is that you can buy windows that truly have individual panes of glass set in a muntin frame or windows simulated to look that way. Simulated window muntins are sometimes referred to as window “grilles” or “grids”. Regardless of what you call them, what’s important to know about window grilles is that they’re available in a variety of styles and each style has an impact on how the window looks, what the window costs and how easy it will be to clean.

True Divided Lites
True divided lites are built like the windows of old – individual panes of glass are enclosed in a muntin framework. This means there’s a separation in the glass at the locations where the glass meets the muntin framework. One downside: multiple panes can make for a tedious window cleaning chore. Individual panes aren’t as efficient as windows with fewer panes or no separations in the glass at all.

Simulated Divided Lite
Simulated divided lite (SDL) windows use simulated muntins on the inside and outside of the window. In a double glazed window with simulated divided lite muntins there’s nothing in between the glass panels. The muntin framework is usually adhered to the glass (non-removable). The muntins are permanently affixed to the glass and the adjoining sash frame which typically makes them more authentic looking. SDLs are almost always a less expensive option than true divide lites. A variation found in double glazed windows employs the grilles sandwiched between the inner and outer panes of glass. Also known as “grilles in the airspace”, some manufacturers offer the option of different colors on each side of the grille to match the interior and exterior color schemes. This type is much easier to clean the window since there’s no physical obstruction on the outer surface of the glass

Window Materials: Pros & Cons
When you’re faced with choosing new windows one of the main considerations is the material choice. And as was stated earlier in this article, a window’s material is governed by what the window frame is made from. Each material has it’s pluses and minuses and the available choices each fit a specific niche in the consideration of performance and cost.

Aluminum Windows
Don’t be confused here by products that are aluminum clad that use an aluminum cover over a material like wood. Aluminum windows have an aluminum frame. In simplistic terms the frame is essentially a box with hollow chambers or channels on the inside. These channels are designed to provide a “thermal break”, or some insulative capacity against temperature transfer through the frame. Because aluminum is a poor insulator, these windows are best used in mild climates.

Aluminum windows are an economical choice and among the lowest in cost relative to other window materials. They have a very strong and rigid which allows for larger window designs (more glass, less frame). They don’t require a lot of ongoing maintenance like period scraping & painting. Aluminum units are available with an anodized (chemically treated) or factory-painted surface for additional durability and resistance to the elements. Downsides include that they are not a good insulator nor an efficient window material given that they readily conduct heat/cold.

Vinyl Windows
Vinyl windows share a similar construction to aluminum windows in that the frame is typically a box construction with hollow chambers that help increase insulation. The obvious difference is that the material is PVC, or vinyl for short. One thing to keep in mind about vinyl is that there are two types of PVC that can be used: plasticized and unplasticized (or uPVC). Plasticizers are additives that give the vinyl flexibility. Some drawbacks of that include a lack of rigidity. Unplasticized vinyl (which some window makers advertise using) is more rigid. However the down-side here is that it becomes brittle and can crack and break. Pluses include that they are economical – among the lower priced window materials, provide an easy to clean and maintain surface, and provide much better insulation compared with aluminum windows. The largest downside is that very few colors are available, thus limiting your decorative options. Moreover they are not paintable, so the color you order is the color you will live with.

Wood Windows
Wood windows are where it all started and they have several benefits. Positive aspects include that they offer superior insulative values and limitless decorative options – you can stain and paint them any color you want. Unclad wood windows are relatively moderately priced – not the cheapest but not the most expensive either, all other factors being equal. Downsides include that wood requires maintenance because paint and stain deteriorate over time. Moreover, wood units if not maintained will deteriorate over time causing poor performance and ultimately requiring replacement.

Clad Wood Windows
Cladding refers to the covering of some material by another. In the case of windows it’s usually a wood window that’s clad in aluminum or vinyl or fiberglass. This presents a good option for getting the beauty of wood on the interior and the benefit of easily maintained surfaces on the exterior. However these can be among the most expensive windows on the market. Note that reduced maintenance costs and long-term longevity will mitigate their initial cost over the long term.

Fiberglass Windows
Fiberglass windows have a lot to offer based on the material properties of the fiberglass itself. You’ll pay more for them than for vinyl, wood or aluminum but the benefits may be worth it to you. You may see the term “pultruded fiberglass” used in association with fiberglass windows. “Pultruded” is simply a way of describing how the fiberglass material is formed into the window framing members. More specifically it describes that method by which the material is heated and pulled through a die to form the frames. Pluses include that the material is strong and isn’t as prone to flexing as, say, vinyl. Further, this material is among the least thermally conductive amongst all window types. Finally, fiberglass can be painted so thus you will have tremendous flexibility as to color. A downside is that this type is relatively more expensive than almost all other window types excepting perhaps clad wood windows.

What To Look For In A Window
Virtually any product made for the home is open to buyer subjectivity and windows are no different. What works for one homeowner just won’t cut it for another. Such is the nature of the wide variety of products available to us.

Low Maintenance Materials
Unless you enjoy doing regular maintenance on your windows, look for materials that will maximize your investment by minimizing the effort required to maintain them. On average, aluminum clad and vinyl windows will require less maintenance – e.g. scraping/painting – to maintain their longevity. That doesn’t mean that wood windows aren’t good windows. Just remember that they will take more maintenance and if maintenance is neglected they may not last as long as windows made from other materials.

Efficient Materials For Your Climate
At a minimum you should choose double glazed insulated glass windows. Single pane windows are just too inefficient. Triple glazed windows are effective in very cold climates. Look for windows with Low-E (low emissivity) coatings. This helps reduce heat loss in colder climates and heat gain in warmer climates. The space between the glass in an insulated glass window should be filled with argon or krypton gas for greater insulation properties. Fiberglass window frames are efficient because they have low thermal conductivity (they don’t translate the heat/cold from the outside to the inside) and they do it better than aluminum or vinyl. If you choose vinyl windows look for products that use thermal “breaks” – technologies and/or features that help insulate the frame such as foam inside the frame channels. The important point is to educate yourself on what kinds of efficient materials make the most sense in your particular environment. You may not need windows with a very low solar heat gain if you live in a northern climate. Conversely, a triple-glaze window (3 panes of glass) might be overkill in a moderate climate that doesn’t experience hot or cold extremes. Choose window options that will work best in your situation.

Select Energy Star Windows
For overall energy efficient windows look for those with the Energy Star rating. These windows meet a minimum criteria for energy savings. Energy Star windows are identified by the National Fenestration Council, an independent, non-profit, third-party that tests and certifies windows that offer better energy performance. Windows that are Energy Star qualified are more than likely going to include some or all of the efficient materials noted above. However it makes sense to look for those features so that you fully understand the quality of the window you’re buying. And there’s nothing that says you can’t exceed Energy Star performance criteria either.

Good Air Leakage Ratings
Air leakage (AL) or air infiltration is the amount of air that passes through your window from the natural crevices, seams and cracks in it’s structure. It’s measured when a simulated 25mph wind pressure is applied to the window. The AL number is expressed as a decimal and represents the amount of air in cubic feet per minute per the square footage of the window (example: 0.3 CFM/sq-ft). Air leakage is important because it’s tied to the energy efficiency of the window. You don’t want cold air blowing into your warm house or hot air into your air-conditioned space. According to the Efficient Windows Collaboration a window with an AL rating of 0.30 or lower is acceptable. Keep in mind however that there are windows with lower AL stats and lower numbers mean better (tighter) windows. Another thing to know is that not all window companies tell you what the air leakage rating is in their product specs or literature. Air leakage testing is currently voluntary among window manufacturers. Some provide it, some don’t. Your best bet is to contact the window maker directly if their window’s AL rating isn’t specified.

An Established Manufacturer
This may seem like it has nothing to do with good window construction but the reputation and track record of the window company you buy from has a lot to do with your ultimate satisfaction. Check to see how long the company has been in business. Some companies come and go while others have survived for a reason. Check the warranty that company has; really read it and use it as a comparison to other window makers’ products. This doesn’t mean you have to go with one of the well-known national brands since there are successful smaller local window makers. Just do your homework on the company. Check the Better Business Bureau for any performance issues.

For Further Reading:
• “Choosing the Right Replacement Windows for Your Home”, Consumer
• “Choosing the Right Windows for Your Home”, Today’s Homeowner:
• “How to Choose and Buy New Windows for Your Home”,

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