Last Updated: Jun 15, 2021
A house without windows would undoubtedly be considered a dreary and bleak place to live, not a cozy place we would love to call home. Windows not only allow for natural light to come into the home and thus reduce the need for artificial lighting, but they also help connect us to the natural world around us through biophilic design. For these reasons, most homes dedicate at least 15% of their total wall space to windows. Unfortunately, windows tend to let lots of heat into the house during the summer months and allow heat to escape during the colder months. A historical study found that in 1990, the energy expenses to offset the heat losses and gains through windows in US homes and commercial buildings totaled 20 billion dollars - one-fourth of the total cost to heat and cool homes.
As sustainable construction methods have advanced, however, more energy-efficient windows have become commonplace in home construction. ENERGY STAR certified windows offer consumers a trusted certification. They will help you improve the comfort of your home without sacrificing that bay window looking out into your beautiful yard.
Most people equate the ENERGY STAR certification with more efficient household appliances. However, the EPAs certification process demands strict energy performance standards and is also applicable to homes, industrial plants, and virtually every household or construction item that either consumes energy or can increase the overall energy efficiency of a building.
ENERGY STAR updated its certification criteria and requirements for windows in 2016 to reflect the best available technologies currently on the market.
ENERGY STAR certified windows have to meet specific U-factors based on the region. U-factors (or U-values) measure heat transfer. The U-factor is the rate a window conducts non-solar heat flow. This measure lets homeowners know how well a window is insulating. The U-factor typically ranges from 0.25 to 1.25; the lower the value, the more energy-efficient the window (and it is the inverse of the R-factor, as used in insulation). In northern zones, ENERGY STAR windows need to have a U-factor of at most 0.27; in southern zones, U-factors can be as high as 0.40 to be meet ENERGY STAR requirements. It should be noted that while these are strong U-factors, the Passive House Institute recommends that windows have a maximum U-factor of only 0.14. This low U-factor ensures the least heat transfer possible, but it can be harder to find in the US market and more costly.
ENERGY STAR windows also must meet strict requirements for solar heat gain coefficient or SHGC ratings. This rating determines the quantity of solar radiation let in through windows. One of the unique aspects of ENERGY STAR certification related to SHGC ratings is that it is very region-specific. This regional aspect is because the more radiation enters your windows, the more heat will enter your home. For example, in northern regions in the US, windows can have any SHGC rating to meet ENERGY STAR requirements because the mild summers mean that excess radiation will not significantly affect the home's thermal performance. However, in hot southern regions, ENERGY STAR windows must have an SHGC rating less than or equal to 0.4 to keep dwellings more comfortable during the long, hot summers. In contrast, south-facing windows will want to have at least a 0.5 SHGC rating for Passive House certification. This requirement is because Passive Homes rely upon sunlight to meet at least 50% of the home's demand for heat.
ENERGY STAR certified windows must comply with minimum qualification criteria for air leakage. An average of 10% of all air leakage in homes occurs through windows, and that number increases in homes with older, single-pane windows. In addition, ENERGY STAR windows must have an air leakage rating of 0.3 CFM per square foot or less. This rating measures the velocity at which air flows into or out of space and ensures that it is low enough to be insignificant to the home's overall energy efficiency.
Opting for single-pane windows or inefficient double-pane windows might save you on the overall cost of your home construction or remodeling project. But, several economic benefits come with opting for ENERGY STAR certified windows, especially if you live in colder climates.
If your home still has single-pane windows, you could potentially save almost $600 per year by switching to ENERGY STAR windows. The average cost of replacing a window in a home is between $450 and $600. However, the savings associated with the home's increased energy efficiency will begin to add up from day one. For example, the ENERGY STAR website estimates the payback period for a home in New York that replaces all of its windows with ENERGY STAR windows at 7.5 years. In hot climates such as Miami, Florida, the potential payback in years for low and average cost ENERGY STAR windows could be as low as 2.5 years.
For instance, aluminum windows usually have a life expectancy of over 30 years. So, the cost-effectiveness analysis for ENERGY STAR certified windows shows that this is a sound investment strategy. It will raise your home's value while also saving you money from reduced heating and cooling bills.
ENERGY STAR certified windows also qualify for federal tax credits that have been extended through 2020. Eligible homeowners can receive a tax credit equal to 10% of the product cost up to $200 for eligible ENERGY STAR windows.
The best windows for your home will depend mainly on your region, the climatic conditions, your home style, and your budget. The window companies listed below are just a few examples of ENERGY STAR certified windows that will help you attain maximum energy efficiency.
This line of Andersen Windows has a U-Factor of 0.20 and an SHGC rating between 0.16 and 0.26. They are designed in a wide range of styles, including casement windows, double-hung windows, and picture windows.
The composite and vinyl windows designed by Interstate have extremely low U-factors, starting at 0.16, which is well below the minimum ENERGY STAR requirements. Vinyl windows tend to be very durable and low maintenance. Still, the main ingredient—PVC—has been criticized as more harmful to the environment from cradle to grave. Fortunately, vinyl is being recycled at a very high rate.
Pella has had a partnership with ENERGY STAR since 1999. Their vinyl 350 Series windows have U-factors ranging from 0.17 to 0.20 and SHGC ratings of 0.22–0.24.
Marvin's Wood Ultimate Double/Single Hung Magnum windows start at an impressive 0.15 U-Factor and range up to 0.20. Their SHGC Ratings vary from 0.14 to 0.50.
Perhaps a full window overhaul isn't viable soon. Still, there are still several things you can do to increase your home's energy efficiency. For example, by merely installing curtains over your windows, you might be able to reduce heat loss through single glazed windows by 60% or more. Double glazed windows are energy-efficient, but a quality curtain can minimize heat loss by up to 50%.
Choosing the best windows for your new home construction or renovation requires homeowners to go beyond aesthetic considerations. ENERGY STAR certified models come in all makes and models. They will also allow you to drastically increase your home's energy efficiency while saving money on your energy bills and limiting your household's environmental footprint.
Tobias runs an agroecology farm and a natural building collective in the mountains of El Salvador. He specializes in earthen construction methods and uses permaculture design methods to integrate structures into the sustainability of the landscape.