A standard window glass does very little to prevent the Sun’s energy from passing through. What is more important for your home, is that it is equally bad at maintaining the infrared heat energy at night, losing it back to the exterior through the process of radiative heat loss.
That’s why, for as long as there have been windows, manufacturers and window installers alike have been looking for things to add to improve their performance. Even in our lifetime, windows used to be manufactured with just one pane. Today, double pane windows are becoming a rarity, with most people opting for sealed units with three panes.
Another common application window manufacturers have developed to improve efficiency are low-emissivity (low-E) coatings.
What is Low-E?
A low-E coating is an invisible metallic layer, only several atoms in thickness, that is applied to glass surfaces. It allows short-wave solar energy to pass while bouncing back out long-wave infrared energy. This allows for most of the sun’s energy to pass through into your home while ensuring a minimal amount of heat in your house is allowed to escape. This is especially beneficial in colder climates as it significantly reduces heat loss from your home in the winter time. Though there is a slight loss in solar gains in your home with the presence of low-E, it more than makes up by significantly reducing solar heat loss in the nighttime.
Why Should You Buy Windows With LoE Glass?
The Low-E coating dramatically lowers the heat loss through the glass. Modern windows with such coating keep your heating costs down at night when there is no sun and maintain a more consistent temperature within your house throughout the colder months.
The key reasons why homeowners should pay close attention to energy-efficient windows with LoE glass:
- Heat loss reduction during the cold season – LoE glass lowers radiant heat transfer and reflects interior heat back to your space, not outside;
- Heat gain reduction during the warm season – LoE glass lowers the flow of hot air from outside into the cooler interior areas of your house during summer;
- Lower Energy Bills – LoE glass balances the heating and cooling energy required to maintain your house at a comfortable temperature. That helps your HVAC system work less, leading to significant energy savings throughout the year.
- Huge Window Areas – An energy-efficient high-performance LoE glass allows homeowners to install windows with huge glass areas without higher energy costs.
Keep in mind that all LoE windows are eligible for ENERGY STAR® certification based on their U-factor, which measures their overall heat loss, forming their overall Energy Rating (ER). It combines their passive solar heat gain (SHGC) via the glass with their overall heat loss and air leakage. Your preferred window must have a U-factor of 1.22 W/m2 or lower or an ER of 34 or higher to be considered energy efficient.