Energy Efficient Windows

Energy-efficient windows can be an invaluable investment for homeowners. Their reduced strain on heating and cooling systems translates to reduced household energy expenses and a smaller carbon footprint. The best guide to finding vacuum insulating glass.

Look out for windows bearing the blue ENERGY STAR label to ensure they meet performance ratings. Critical performance criteria may include U-factors, solar heat gain coefficients, air leakage, and visual transmittance ratings.


The U-factor of windows and doors is an essential indicator of their energy efficiency. It shows the rate at which nonsolar heat travels through them and, thus, how well they insulate. A lower U-factor indicates greater efficiency; however, other factors must also be taken into account to understand its influence on overall energy performance.

ENERGY STAR promotes energy-efficient products like windows in order to lower greenhouse gas emissions, save homeowners money on energy bills, and prevent the waste of fossil fuels and electricity. In order to achieve this goal, any new construction or renovation must thoroughly analyze all building components to understand their functions and how they interrelate – with the U-factor having an enormous effect on energy efficiency as well as how much of your heating/cooling budget goes toward paying for heating/cooling expenses.

Homeowners should also consider other energy rating characteristics when comparing windows for efficiency. These include solar heat gain coefficient (SHGC), air leakage, and visible transmittance ratings provided by NFRC; they indicate how efficiently windows perform in different climate zones and reflect frame material, glass type, and spacer materials used.

A window’s U-factor is determined using a standardized test designed to measure thermal conductivity under specific conditions and accurately represent its insulating capabilities. The test simulates real-world scenarios while accurately reflecting window performance.

For example, the ENERGY STAR standards for windows installed in northern climate zones stipulate a U-factor of no higher than 0.27 and SHGC of no greater than 0.17; however, alternative ways may suffice, such as having a smaller frame size or using low-e coating.

Watch this video to learn how to read a window’s National Fenestration Rating Council (NFRC) label and compare and contrast different window models’ energy performance ratings. NFRC labels feature four main energy performance categories: air leakage, visible transmittance, U-factor, and condensation resistance. Each window can be broken down into these categories so homeowners can easily compare and contrast the energy ratings of various models.

Solar Heat Gain Coefficient

The solar heat gain coefficient, or SHGC, measures how much solar energy passes through windows into interior spaces. Similar to U-factor measurements, SHGC ratings represent how much radiant heat comes into a home from sunlight through windows—expressed as an integer number between 0 and 1 (the lower the rating, the more effective window products will be at reducing air conditioning load during summer months and energy bills overall). Window products with lower SHGC ratings tend to reduce air conditioning loads and energy bills overall more efficiently than their competitors.

As with the U-factor, SHGC ratings take into account aspects such as frame material, glass type/coatings/coating thickness/coats, and glazing sealants when assessing the energy performance of windows. NFRC provides uniform ratings that take both SHGC and Visible Transmittance (VT) into account when assessing energy performance of a window’s energy performance; these figures are displayed on its label alongside U-factor and condensation resistance measurements.

As a general guideline, the higher the SHGC number, the more solar heat passes through a window. For instance, windows with an SHGC of 0.3 allow 30% more solar energy through than those with an SHGC of 0.25.

SHGC ratings also depend on climate. Northern regions tend to require higher SHGC values to allow sunlight to act as a natural heater during the winter, while southern locations will need lower ratings in order to avoid excess heat build-up in their buildings during summertime.

No matter where you reside, ENERGY STAR-certified windows are tailored to meet specific energy requirements in any region, providing homeowners with cost-effective options that will reduce heating and cooling expenses year-round. By considering both SHGC ratings as well as other criteria outlined above, homeowners can select windows and skylights best suited to their home’s specific conditions.

If you need help selecting windows suitable for your home, contact a certified ENERGY STAR contractor or visit the National Fenestration Rating Council website (NFRC). The NFRC offers a listing of certified products by brand and frame material and an online tool for searching by zip code and climate zone.

Air Leakage

When it comes to selecting windows, doors, and skylights that prevent heated or cooled air from escaping your home, few options surpass those marked ENERGY STAR. These products adhere to stringent energy efficiency guidelines established by the Environmental Protection Agency (EPA), offering homeowners significant utility savings while improving comfort levels.

ENERGY STAR-certified windows are specially crafted to reduce air leakage, which puts unnecessary strain on your HVAC system. Their construction incorporates features that minimize heat transfer, such as Low-E glass, multiple panes, and insulated frames; moreover, they often include hinged openings, such as casements and awnings, which are less susceptible to air leakage than single—or double-hung windows.

Before purchasing an ENERGY STAR window, it’s essential that you understand its rigorous certification process and become informed about its various ratings and how they relate to one another. In order to meet ENERGY STAR certification criteria in your climate zone, windows must meet specific U-factor and Solar Heat Gain Coefficient (SHGC) standards set by government authorities.

As a homeowner, when searching for energy-efficient window replacements, the U-factor should be your top consideration. A lower U-factor means more insulation.

While a window’s U-factor rating should always come first in your decision-making process, other aspects, such as Solar Heat Gain Coefficient (SHGC) and Visible Transmittance, should not be discounted either. SHGC determines how much radiant heat enters a home through windows; for those living in northern states where keeping warm is a top priority, higher SHGC values may be preferable, while those in southern regions seeking cooling should prefer lower values.

Air Leakage Rating is an essential aspect to consider, yet its interpretation can often be misleading. That’s because air leakage ratings are calculated based on wind speed, which doesn’t represent typical conditions in certain areas across the United States, and are measured as cubic feet of air per square inch window frame over one minute—two measurements that can lead to incorrect comparisons between windows.

Visual Transmittance

When replacing or building new windows, energy-efficient options should always be prioritized. Energy-star windows are specifically designed to keep air and heat within your home where they belong—cutting energy costs by up to 12%! They do this by minimizing light passing through them through visible transmittance (VT).

When purchasing energy-efficient windows, the key to selecting ones with high VT ratings is to consider other factors as well. You should examine the u-factor, solar heat gain coefficient, and air leakage to gauge how well your windows perform overall.

One of the main complaints from homeowners who have recently had their windows replaced is feeling cold despite turning on the air conditioning. This may be because their old windows let in heat from outside that is then drawn back out through windows; by contrast, energy-efficient ENERGY STAR windows trap more of the sun’s heat inside, providing more comfort to residents.

Before embarking on any home renovation, it’s essential to do research first. Energy Star windows have been independently certified by the National Fenestration Rating Council (NFRC) for their quality. Their standards include U-factor, solar heat gain coefficient, air leakage, and visible transmittance ratings. Requirements may differ depending on where you reside, so it’s wise to check which are necessary in your region before purchasing windows.

When shopping for new windows, be sure to look for windows bearing an ENERGY STAR label in the bottom left corner of each frame. This signifies they meet NFRC standards set by the Environmental Protection Agency. Likewise, find a professional window contractor that uses ENERGY STAR products so you can ensure you’re receiving optimal quality and performance from your new purchase.

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