Thinking about replacing your windows?

A window’s impact on your home’s comfort level and energy efficiency depends on two variables: its features and the setting in which it is installed. When windows drive your monthly utility bills lower, it’s not just because they are embedded with all the current technologies – it’s because those features combine in ways that fit a home’s climate and immediate surroundings. The right fit won’t just help lower your monthly utility bills – you might also be able to spend less on heating and cooling equipment if that investment is in your near future. Making the right choice doesn’t have to be difficult.

The conclusions shared here are based on research using our Window Selection Tool, which searches by ZIP code to find available windows for purchase that meet your specific needs. It also provides users with an estimate of the cost savings on monthly utility bills when compared with older, inefficient windows. Our researchers reviewed 20 types of windows in three sizes and with five different levels of shading around them. Here are the main conclusions:

Sun shining

SOUTHERN EXPOSURE: In any climate, southern-facing windows offer the greatest warmth from the sun from outside to interiors, and that makes them valuable when the weather is cold. Windows that face west offer the second-greatest exposure, followed by eastern and then northern exposures. Annual energy costs for a typical house in Minneapolis with standard double-pane windows facing primarily southward were calculated at slightly under $1,400 in our study and slightly higher than that threshold if most windows look in other directions. This amount drops by about $200 per year if the windows feature efficient materials in their frames, and the glass has a low-e coating, a clear and thin film that helps block unwanted solar rays but keeps the warmth we want.

Choosing windows

SIZE NO LONGER MATTERS: You don’t need small windows to improve a home’s energy efficiency. Our research shows modern technologies narrow the gap. To test the impact of window size, our researchers ran simulations using windows with a square footage roughly 10% of that of the square footage of a test house (small) and then with windows at 15% of the total square feet (medium), and at 20% of the total (large).

In cold climates, having small windows delivered a $200 annual savings compared with large ones. But adding low-e coating and efficient window frames narrows that gap to about $50.

shade window

SHADE NEEDS: Our research shows that shade devices are crucial in hot climates but less so in cold ones. In a typical house in Minneapolis, an overhang installed over windows could be useful to block heat infiltration in summer but allow it in the winter because the sun is lower in the sky, and solar rays will hit windows at lower angles. Interior solutions such as drapes, blinds, and curtains also play a role.

With double-pane windows and shading options, the average annual energy cost can fall from almost $1,600 to about $1,500. Adding in low-e coating drops the range to between $1,400 and $1,300.

natural light

COMFORT: The Window Selection Tool’s comfort metric is the only statistic currently available to measure the comfort level a window can provide. Our Minneapolis scenarios show that the greatest efficiency comes with installing windows with a low “u-factor” – a measurement that estimates the amount of heat that can escape. U-factor is one of three main energy-efficiency ratings the Window Selection Tool uses for its calculations, and you can read a two-minute explainer here.

The best window replacement option is not always obvious, so it is important for homeowners and designers to know the advanced technologies and to use calculation tools, such as the Window Selection Tool, to improve design choices for energy-efficient homes. The more you know, the better choice you can make.

Interested in how much energy-efficient windows could be saving you? The ENERGY STAR savings estimates for windows are based on energy calculations. Check the page here.