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When selecting new windows, there are a few considerations that must be straightened out before you can install. The most important is the material that will be used. The material used to make the window frame has the biggest influence on efficiency and aesthetics. Efficiency and aesthetics are the two most important criteria when choosing new windows. You need your new windows to keep heat in your house in the winter, and out of your house in the summer. You also want the frame to match the look of your home and add to its aesthetic value. Here at Starcom, we install three different types of windows; vinyl, wood, and fiberglass. Each has its own list of pros and cons. Depending on your situation, one option might be better than others. Let’s look at the three options and figure out which is the best choice for your home.
Vinyl windows are made from polyvinyl chloride (PVC) with ultraviolet stabilizers to minimize yellow tinting from the sun. PVC is very pliable and easy to manipulate, making vinyl a good option for custom made windows. This pliable nature also means vinyl is at risk in certain conditions. Depending on moisture and temperature levels, PVC can warp, shrink, and expand; leading to unsealed gaps in the frame, letting air in and out of your home. Vinyl windows are very low maintenance and will last for 20-40 years (How Long do Vinyl Windows Last?, 2016). Even after their usable life, you can recycle them to be melted and formed into new products. They provide a sleek look and can be easily cleaned with soap and water. They are also the cheapest option of the three that we are looking at, but price should not be ruling your decision. There is a lot to consider and a premature decision based solely on price may lead to some problems down the road.
Fiberglass window frames showed up on the market in the early 2000’s. Since then they have grown in popularity exponentially. Fiberglass is made of polyester resins that are activated by a catalyst. This is then pulled through a heated die. A die is a specialized tool that is used in manufacturing to cut, shape, or mold different materials (Wallender, 2019). The finished product is called a lineal and can be machined and formed to fit any shape. Fiberglass seems to have been developed as a newer and higher tech version of vinyl. They have many similar characteristics but fiberglass does better in almost every category. Fiberglass is eight times stronger than vinyl and does not shrink or warp. It is exceptional in insulating a home. Unlike vinyl, it does not get weaker over time because of UV light. It is extremely low maintenance like vinyl but costs more than vinyl, but less than wood. It’s such a strong and rigid material that it will never bend or crack because of moisture problems. It is also easily cleaned but cannot be readily recycled like vinyl can.
Wood framed windows are simple and elegant. They do not provide much in the way of technologic features but provide good insulation through the natural ability of wood to insulate. The most common wood used is pine, which insulates very well. Wood frames require much more maintenance than vinyl or fiberglass windows. They must be stained, sealed, and painted to minimize the
risk of rotting, warping, and bending. At Starcom we work with only the best suppliers who use the highest quality materials. So you can be assured that maintenance will be kept at a minimum with our wood windows. Wood window frames are very popular in historic neighborhoods and old homes as the rustic look that wood frames provide pairs well with older homes.
As I stated, efficiency in holding heat in or out is the most important quality of a window. Each material has its own level of ability to resist transferring heat. This is its thermal conductivity. The way to measure a material’s thermal conductivity is with the equation W/mK. This stands for Watt per meter by Kelvin.
Watt per meter by Kelvin (W/mK)
If a material has a high W/mK, it has high thermal conductivity and can absorb and pass on heat easily. If it has a low W/mK, then the material will not absorb and release heat efficiently. This is what we want for proper insulation; little to no heat transfer through the windows. For example, aluminum is known for being able to absorb and release heat very quickly. Think of using aluminum foil when cooking. When you take the foil out of the oven, it’s not hot for long. It releases most of its heat into the air very quickly. Aluminum has a W/mK value of around 220-240. Let’s look at wood, vinyl, and fiberglass’ thermal conductivity. Pine is the most common wood in window frames so we will use its figures to compare to vinyl (PVC) and fiberglass. Pine’s W/mK value is 0.12, PVC’s W/mK value is 0.19, and fiberglass’ W/mK value is 0.04 (Thermal Conductivity of Common Materials and Gases). Looking at these numbers, it is easy to see why fiberglass is rated as the most energy efficient material to use for windows.
Watt per meter by Kelvin is needed in figuring out a material’s R-value. An R-value is the measure of a materials resistance to heat flow. Its formula is R= I/λ. Where I equals the thickness of the material in meters, and λ is the W/mK value. The higher the answer to this equation, the better the material is at insulating. The answer is written as meters squared Kelvin per Watt (m^(2)K/W). The R-Value is a great way to measure insulation capability because of its inclusion of insulation thickness. For example, if we compare a one inch slab (.0254 meters) of PVC and a one inch slab of fiberglass, we will find that the PVC’s R-value is .0254/.19=.13^(2)K/W and fiberglass’ R-value is .0254/.04=.635^(2)K/W. Fiberglass clearly has the higher R-value, indicating it is the superior material for heat resistance.
So why is R-value important? As we’ve stated, R-value measures a particular material’s resistance to heat transfer. R-value is needed to find the U-value of a window. U-value measures the rate of heat transfer through conduction and radiation (Understanding R-value and U-value, 2017). It is the final measurement of a window’s ability to insulate. The lower the U-value, the more capable the window is as an insulator. The formula for U-value is 1/R and is measured in Kelvin meter squared per Watt (Km^(2)/W). If you want to find the U-value for a window, you must find the R-value of each material used, add them up, and then divide 1 by your answer. Looking at our examples using PVC and fiberglass, we find that they have U-value equations of 1/.13^(2)=59.17 Km^(2)/W and 1/.635^(2)=2.48 Km^(2)/W respectively. This shows that fiberglass is a much more superior insulator than the PVC used in vinyl windows.
Between the Panes
The material that makes up the frame is not the only factor in determining efficiency. Many manufacturers include extra features that increase efficiency in keeping warm air where you want it. Some windows use multiple panes of glass, some use clear coatings on the glass, and some even use noble gases floating in between panes to further increase efficiency.
Double/Triple Pane Windows
Having more panes gives you a better chance of having efficient features installed into your window. A double paned window gives you an opportunity to use gases with low U-values to further decrease the windows ability to transfer heat into or out of the home. A triple pane window will only increase the window’s efficiency. It is vital to choose correct materials when choosing double and triple paned windows. Double or triple paned windows in wood frames are at risk of warping and bending over time so choose vinyl or fiberglass (Novotny). If you want a triple or even quadruple pane window, choose fiberglass as it has the best strength and rigidity.
Manufacturers can add microscopically thin clear coatings to the glass for extra defense against UV and infrared light. UV rays will fade fabrics and tint vinyl yellow. Infrared causes heat to radiate into your home. Low-e coatings have been designed to minimize your home’s exposure to UV and infrared rays while letting all visible light shine through (Glass). Emissivity is an objects ability to absorb and radiate energy. This is where the low-emissivity (low-e) coatings come into play. When heat is trying to enter or exit your home through your windows, it is bounced back in or out by the low-e coating, as the coating has very little ability to absorb and redistribute the heat.
Often, manufacturers will insert a noble gas like argon in between each window pane. Argon has very low thermal conductivity and very high resistance to heat transfer. With a space between the glass of half an inch, argon gas has an R-value of .0127/.016=.79^(2)K/W. This leads to a U-value equation of 1/.79^(2)=1.60 Km^(2)/W. For reference, a half inch of fiberglass has an R-value of .0127/.04=.3175^(2)K/W, and a U-value of 1/.3175^(2)=9.92 Km^(2)/W. With a U-value nearly six times less than that of fiberglass, it is easy to see why so many manufacturers use argon to maximize heat resistance and minimize heat transfer.
Below is an illustration showing a multi-pane window with low-e glass and a gas fill.
The Last Word
Now that you know all about maximizing your home’s efficiency using your windows, always remember that you will need proper installation to take advantage of all the features and advantages that new windows delivers. Here at Starcom, we can assure you that we hold our standards to the highest and work with only the top manufacturers in the area. You can be sure that we will install each window perfectly and exactly to your specifications.
Glass, V. A. (n.d.). How Low-e Glass Works. Retrieved July 16, 2019, from http://glassed.vitroglazings.com/topics/how-low-e-glass-works
How Long do Vinyl Windows Last? (2016, May 26). Retrieved July 16, 2019, from https://www.newmanwindows.com/long-vinyl-windows-last/
Interesting Facts about Vinyl Windows. (2016, August 25). Retrieved July 15, 2019, from https://www.pelicanreplacementwindows.com/interesting-facts-about-vinyl-windows/
McNutt, A. (n.d.). Choosing Energy Efficient Windows for Your Home. Retrieved from https://www.hgtv.com/remodel/interior-remodel/choosing-energy-efficient-windows-for-your-home
Novotny, E. (n.d.). Double Pane or Triple Pane Replacement Windows – Which is Best? Retrieved July 16, 2019, from https://www.windowsonwashington.net/blog-full/double-pane-or-triple-pane-replacement-windows-which-is-best
Patterson, J. E., & Miers, R. J. (n.d.). The Thermal Conductivity of Common Tubing Materials Applied in a Solar Water Heater Collector. Retrieved July 15, 2019, from http://ascpro0.ascweb.org/archives/cd/2010/paper/CPRT1-410-997-7700.pdf
Thermal Conductivity of Common Materials and Gases. (n.d.). Retrieved July 15, 2019, from https://www.engineeringtoolbox.com/thermal-conductivity-d_429.html
Understanding R-value and U-value: Norbord - North American Products. (2017, July 5). Retrieved July 16, 2019, from https://www.norbord.com/na/blog/understanding-r-value-and-u-value/
Wallender, L. (2019, January 27). Vinyl vs. Fiberglass Windows: Which One Is Best? Retrieved July 16, 2019, from https://www.thespruce.com/vinyl-vs-fiberglass-windows-1-410-997-7700
Window Types and Technologies. (n.d.). Retrieved July 15, 2019, from https://www.energy.gov/energysaver/window-types-and-technologies
All pictures taken from pella.com, and US Department of Energy.