Technical Glossary

Measures how much air will enter a room through a product. AERC certified products with lower air leakage may result in fewer drafts and help to reduce heating costs.

The Cool Climate number – or rating – indicates the amount of energy that you can save by using the window attachment if you live in a cooler climate (where you turn on your heat most of the year), compared to not using a window attachment at all. In other words, if the window attachment you are interested in buying has a Cool Climate rating of 64, installing the attachment over an existing window in your home will save 64% of the energy that would otherwise be lost without the attachment.

Window unit with two panes of glass sealed into a single glazing unit; gas between the panes insulates the window.

Double Pane with Clear Glass is a type of window that provides strong thermal performance: good resistance to heat loss, high solar heat gain, and high visual transmittance.

Double Pane windows with Low-E glass provide high resistance to heat loss and can be utilized for solar gain but with some loss of visual transmittance.

How readily the surface of a material gives off heat by radiation. Many common building materials have “high” emissivity (around 0.9 out of 1.0 being a perfect emitter), while materials or objects with metallic coatings or surfaces have “low” emissivity (around 0.15 or less).

Nearly invisible metallic coating on inside surface of double-pane glass windows, storm windows, and interior window panels that improves the energy efficiency of the window and the thermal comfort of occupants.

Single Pane Clear Glass windows, commonly found on older homes, provide the weakest thermal performance but highest visual transmittance amongst window types. The window unit has just one pane of glass.

Measures how well a product can resist unwanted heat gain. AERC certified products with lower SHGC means there is less heat gain, which may reduce cooling costs, while products with higher SHGC means there is more heat gain, which may reduce heating costs.

Measures how well a product can retain heat and keep it from escaping from the inside of a room. AERC certified products with a lower U-Factor means there is less heat loss and should be considered by those concerned about heating costs.

Measures how well a product is designed to effectively light your home with daylight. AERC certified products with higher VT means more light enters, which may help reduce need for artificial lighting, leading to reduced utility costs.

The Warm Climate number – or rating – indicates the amount of energy that you can save by using the window attachment if you live in a warmer climate (where you use your air conditioning most of the year), compared to not using a window attachment at all. In other words, if the window attachment you are interested in buying has a Warm Climate rating of 64, installing the attachment over an existing window in your home will save 64% of the energy that would otherwise be lost without the attachment.