What Makes Replacement Windows Energy Efficient?

One of the biggest selling points of brand new windows? Energy efficiency. You’ve probably heard the claims, “Lower your monthly energy bills and help Mother Earth!” and  “Windows have an awesome return on investment!” But let’s look at the hard science for a minute here. What do people mean when they say windows are energy efficient? And what’s the supporting science? Simply put, your custom replacement windows act as barriers. In the winter they keep the cold out, and in the summer they keep the cold in.  So what exactly allows them to do that? And why might one type of window be better at it?

Let’s talk about heat transfer

You may have been asleep in science class the day the laws of thermodynamics were explained, but we all know that your hot coffee is eventually going to come to room temperature. On a hot day, the ice cubes in your drink are going to melt. This phenomenon is called heat transfer.  A well-made window acts like a thermos, and cuts down on heat transfer. Windows are made up of two parts— the glass and frame. Because the glass takes up the majority of the space, it has a big role to play in heat transfer.  Scientists have been hard at work on window glass. A simple single-pane glass window will allow 85%-90% of heat to pass through it in either direction. If we double up the glass only 67%-73% of heat passes through. Triple it up and you’re down to 57-65%. However, you can’t go too crazy here or the window gets too heavy to open.  How about altering the glass itself? Scientists found that if they baked a little bit of tin or silver oxide into the glass they could keep your home more comfortable. Metal reflects solar energy. The standard is two layers of silver per window, but you can get three if you're really serious. At the high end, if you get triple silver low-e reflective coating, you only let 2-5% of the heat pass through. Impressive.  But let’s think beyond the glass, shall we?

Frame and sash material

How about the material that holds the glass in place? Imagine it’s a hot day and you see a shiny metal park bench. No way you are sitting on that thing— you’d burn your bottom. Wooden park benches are much more tempting. Metal conducts heat, and is a poor choice for window sash material. Wood window frames are about twelve times more energy efficient than metal.  However, wood and metal windows don’t have weather stripping. They still aren’t the best material to surround your glass. Without weather stripping, you’ll have a drafty window.  Vinyl is the big break-through material. Insulated vinyl framing is about four times more efficient than wood. The weather stripping can be built right into the vinyl. There’s no need to use adhesives that can break down over time.  Let’s put all that new science vocab into one big show-off sentence:  The most energy efficient windows cut down on heat transfer and are made with insulated vinyl frame material and glass with silver oxide-based low emissivity coatings.   Check out the big brain on you. 

Be an Energy Star

The good news is that someone has already done the leg work on energy efficiency.  Energy Star is a program run by the EPA and U.S. Department of Energy that researches energy efficiency. They run independent trials on dishwashers, refrigerators, and yes, windows. In 2019 alone, ENERGY STAR worked to help Americans save almost $39 billion dollars in energy costs. If you check out their website, they’ll give you suggestions for windows for your region, and let you know just how heavy duty you need to go for your climate. 

Don’t let them leak

Remember that thermos keeping your coffee hot? The best thermos in the world does you no good if you don’t screw the lid on tight. Carelessly throw that thermos in a backpack and you’ve got coffee everywhere.  The best window in the world will leak if not installed properly. Proper window installation is key. Every window installation team at Window Nation is factory trained. We specialize in window replacement— and have installed over one million windows since 2006.  We’ll make sure the most energy efficient windows are the windows proudly hanging in your home.  Give us a call.