How to Understand Insulated Windows
- 1). Find the "Energy Performance Ratings" sticker on the window. This gives you the ratings on several parameters and will be where you gather the information to interpret.
- 2). Confirm that the window has insulated glass, represented by an IG on the manufacturers details. Insulated glass uses two panes of glass with air captured between the two panes to serve as an insulation barrier.
- 3). Read the U-factor rating. This value measures your window's ability to reduce heat loss from indirect exposure. Seek a lower value that means the window is allowing less heat to be transferred out of the house, thus saving you energy costs. Most efficient windows range between .22 and .30 U-factor.
- 4). Find the solar heat gain coefficient; this should be the value next to the U-factor. Where the U-factor measures indirect radiation heat loss, the solar heat gain coefficient measures heat gain from direct radiation. This means that the sun will warm your home through the glass through hot summer months. A lower solar heat gain coefficient means the window is helping to retain the coolness within the home by not pulling excess heat from outside.
- 5). Read the viable transmittance rating. A high viable transmittance tells you how much light will be allowed through the window to maximize daylight hours. Most windows are between .3 and .8.
- 6). Confirm a low air leakage rating that rates how much air per cubic foot passes through the window, mixing external and internal temperatures.
- 7). Look for a high condensation resistance, which means that the window is less likely to develop condensation when temperatures vary from inside to outside. This number will range between 0 and 100. Good windows will be in the 50s or less.
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