How to Understand Energy-Efficient Window Ratings

As you shop for new windows, it can feel overwhelming trying to understand their energy ratings. Here are the most prevalent terms used to describe the energy efficiency of replacement windows. Armed with this knowledge, you’ll be well equipped to conquer the “which type of replacement window to choose” decision with ease. Keep in mind that window performance is directly impacted by who installs them.  

Raise Your Comfort Level and Lower Your Utility Bills with Energy-Efficient Windows

Let’s take a moment to identify the energy-efficiency codes and numbers you’ll come across on new windows. 

U-Factor

U-factor describes the rate at which a window transmits non-solar heat flow. It refers to the entire window’s performance including the glass, glazing, frame, and spacer material. 

Remember – The lower the U-factor, the more energy-efficient the window is. 

Solar Heat Gain Coefficient (SHGC)

Solar heat gain coefficient—also referred to as SHGC—indicates how well a window blocks the sun’s heat. Solar radiation is transmitted directly and/or absorbed, and subsequently released as heat inside your home. A window with a low SHGC rating will be more efficient at lowering cooling loads throughout the summer as it blocks heat gain from the sun. A window with a high SHGC rating is more efficient at collecting solar heat during the winter. Your area weather, your home’s orientation, and how much external shading it has all factor into the best SHGC rating for your replacement windows. 

Remember – SHGC is displayed as a number between zero and one. The lower the number, the better. The lower the SHGC, the less solar heat the window transmits. 

ENERGY STAR® Certification

ENERGY STAR qualified windows will make your home more comfortable throughout the year. They filter out damaging ultraviolet light and save you on heating and cooling bills. To qualify for ENERGY STAR certification, a window must meet strict standards such as: 

• Double or Triple Pane – Multiple panes ensure your home will be well shielded from the elements and outdoor temperatures. Gas (such as argon) placed between the panes insulates against heat flow into or out of your home. 
• Window Frame Materials – These must be designed to increase the window’s insulation capabilities. 
• Spacers – These keep a window’s glass panes the proper distance apart to decrease heat flow and avoid condensation. 
• U-Factor – This measures a replacement window’s resistance to heat loss, and the lower the number, the better the energy performance. 
• Low-E Glass – A window’s special coatings create low emissivity (Low-E) glass. This glass prevents heat energy from going into or out of your home, contributing to your house’s insulation. It also lowers the amount of ultraviolet (UV) light that enters your home, and significantly safeguards your furniture from fading. 
• SHGC – This number measures how much heat enters your home through window glass, and the lower the number, the better the energy efficiency. 

Air Leakage

Air Leakage (AL) is the rate of air movement around a window. A window with low air leakage rating is tighter than one with a higher AL rating. 

Remember – The lower the AL, the less air will pass through cracks in the window unit. 

Energy-Efficient Window Shopping Tips 

Don’t Underestimate the Importance of Proper Installation

The most energy-efficient windows can’t do their job properly unless they are installed with precision by an experienced contractor. Installation is vital to the long-term performance of your windows, so find a reputable local team with rave reviews (like us!). 

Check for ENERGY STAR Rebates

Find out if ENERGY STAR windows are eligible for the federal tax credit or other incentives. Your local utility company may offer incentives. 

Update Your Home with Modern Windows That Increase Its Comfort and Beauty

Don’t settle for subpar windows that leak your heating and air conditioning in exchange for allowing outdoor temperatures to invade your interior. Get premium fiberglass replacement windows that lower your utilities, increase indoor comfort, and preserve your HVAC unit. 

At Replacement Windows by Lakeside, we exclusively install Infinity from Marvin Fiberglass replacement windows. Since 2006, as St. Louis’s exclusive distributor and authorized contractor for Infinity from Marvin, we ensure precise installation that delivers the long-term high performance you deserve. 

Our in-house installation teams prioritize quality control. Replacement windows are backed by our workmanship warranty and the manufacturer’s warranty. Learn more about how our window services can provide the comfort and energy-saving solutions you need for your home.