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.
What are the different applications of Low-E coatings?
A great advantage of the low-E add-on for your new energy efficient windows is that you as a consumer have a choice as to just how much insulation you want in your window. A single low-E coating on one pane in a double-pane unit would likely have a similar insulation value as a standard triple-pane unit.
There are three common applications of Low-E coatings for residential windows:
LoE 180 – the standard low-emissivity coating helps keep the warmth inside your home and reduces harmful effects of UV. Most companies that manufacture vinyl windows offer LoE 180 included in the price of the window. Recommended for north facing windows.
LoE 272 – a more advanced coating for even better insulation and reduced heat loss. Great for rooms all around the house.
LoE 366 – has the same insulating values as LoE272 but with added protection from the sunshine. Reduces up to 95% of damaging UV radiation. Especially recommended for unshaded South and West facing windows.
Although historically Low-E coating was applied in a “soft-coat”(low heat loss, low solar gain) and “hard-coat” (moderate heat loss, high solar gain), recent developments in technology are erasing the differences between the different low-E applications. Today most low-E coatings can be classified as high solar gain, medium solar gain, and low solar gain.
While it is good to choose an energy-efficient product from the start, it is easy to optimize your window replacement by selecting low-E properties for your exact needs. Windows that face south or east can maximize the passive solar energy intake with high solar gain low-E. Conversely, you may want to have a low solar gain glazing on west-facing windows as it often helps keep the room cooler in the summertime. Low solar gain coating is also good for north facing windows as it allows for the least amount of heat loss in windows that get minimal sunlight.