One question our installers sometimes get is “what does U factor mean?” It’s a term that some homeowners might have heard in conversations with others in the window industry or from an energy efficiency consultant.
Whether you’re a new homeowner who’s wondering how you can mitigate your electricity bills for years to come or are just curious about the industry standard terms that window salespeople and installers use, knowing these terms can be a huge help. Let’s demystify one of these industry standard terms for you:
What Is U Factor?
U factor, sometimes called U value, is, simply put, a measurement of how well a window insulates a home on a 0 to 1 scale. The lower the U-factor, the better the window will insulate your house. A U factor measurement of 0 would be perfect insulation, while a value of 1 would mean that the window provides no insulation whatsoever.
What About R-Value?
Energy efficiency experts might also mention R-value, which the International Association of Certified Home Inspectors notes is “used to rate the energy efficiency of insulation installed in other areas of the building envelope, such as beneath the roof.”
To determine the R-value of a window, you can divide 1 by the U factor of the window. For example, if your window’s U factor were 0.33, its R-value would be roughly 3.33. If the U-value was 0.25, then the R-value would be 4.
Why U Factor Matters
The big reason why you might care about the U value of your windows is that it has a direct impact on the cooling costs for your home. Keeping the hot air out in summer has a major impact on your energy bill for running your AC.
If you have windows with extremely low U-factor values, then you won’t gain as much heat from the outside when you’re running the air conditioning or lose as much heat from your home when you’re running the heater during the cooler months of the year.
So, if you find yourself frequently running the AC during the hotter months, then this is an important consideration to make when upgrading your home’s windows.
Windows with features such as several panes of glass, argon gas-fills, ‘low e’ coatings, and high-quality glazing will have better U-values than windows that are single-paned with poorer-quality glazing.
What Else Should I Consider for My Windows When Measuring Energy Efficiency?
1) SHGC (Solar Heat Gain Coefficient)
In addition to U-factor for windows, you also might want to consider the Solar Heat Gain Coefficient (SHGC) value of the windows you want to install.
In fact, for most Floridians, the SHGC measurement of their windows can be especially important during hot, sunny days. As noted by Energy.gov, “The SHGC measures how much of the sun’s heat comes through the window. It can range in value from 0 to 1.”
The lower the SHGC, the less heat it lets in. This is useful for keeping your home cool during the hot summer months. Windows facing the East and West where the sun rises and sets should have especially low SHGC values (or be given shade) to minimize heat gain in summer.
2) Other Insulation in Your Home
Having an extremely low U-factor on your home’s windows will have a major impact on your AC bill, but it’s not the only factor to consider. When updating your home for energy efficiency, it’s important to consider the insulation in your walls, ceiling, attic, and other regions of the house.
Installing energy-efficient windows with low U-factor and SHGC values can be the perfect capstone to your energy efficiency remodel, but updating your insulation is also important if you want to have the maximum benefit.
3) Installation Quality
The U-factor of the window might not matter if the install job is handled poorly. The complete window assembly, from the glass to the frame, spacer, glazing, sealant, shims, insulation, and weatherstripping can all affect how much heat is lost from the window.
So, when choosing installers for your energy efficient window upgrade, it’s vital that you choose a proven, reliable partner with a long track record of success in the greater Tampa area. Look for things like quality guarantees, positive reviews, a high BBB rating, and whether they use in-house installers or subcontract their work out to third parties.
Here at Karoly Windows & Doors, we use composite shims, medium density expanding foam, RWD vinyl, Duo-Sil caulking, and 100% in-house installers to ensure a top-quality installation that creates a strong seal.
4) Air Leakage
As noted by the U.S. Department of Energy, air leakage is “the rate of air movement around a window, door, or skylight in the presence of a specific pressure difference across it.” A window with a high air leakage value tends to let out more heat than one that has a low air leakage number.
A large part of the air leakage of a window is the quality of the install job. A well-done insulation will provide a tighter seal than one that is done poorly. The air leakage rating on any given window typically assumes a proper installation.
5) Sunlight Transmittance
The amount of sunlight that a window lets through is referred to as its ‘visible transmittance’ or VT, expressed as a value between 0 and 1. Windows with high VT let in more light than ones with low VT.
You might assume that this means that you should get a window with a low VT… however, there’s more to it than that. You also need to consider the light-to-solar gain (LSG). LSG is the ratio between the VT and the solar heat gain coefficient from point one.
Some windows that have dark films or coatings might keep out the visible light of the sun without blocking the heat of the sun. Or worse, they may retain that heat and release it into the home throughout the rest of the day.
The tricky thing is that not all windows include an LSG rating in their stats. Ideally, you want a window with a high LSG value, since that indicates that the window will let in more light without letting in lots of the sun’s heat.
How Do I Choose the Best Windows for Energy Efficiency?
Balancing U factor, SHGC, VT, and other elements of a window’s energy efficiency can be challenging. But you don’t have to do it on your own.
Consulting with an expert from Karoly Windows & Doors can help you find the right window with the right balance of U factor and other energy efficiency metrics to meet your needs. Contact us today to get started!
