Reading the Energy Label on a New Window

Two windows that look the same in a showroom can differ by a wide margin on the label, and the notes at san bernardino window contractor ptag online start with those numbers. A window replacement in San Bernardino, CA is judged by the NFRC sticker, which lists the figures a contractor and an inspector rely on.

U-factor

The U-factor measures how fast heat moves through the whole window, frame included. A lower number means better insulation. It matters most on cold nights and hot afternoons alike, because heat passes in whichever direction the temperature pushes it. Vinyl window frames and fiberglass window frames usually score lower than bare aluminum.

Solar heat gain coefficient

The SHGC, from zero to one, shows how much solar heat gets into the room. In the hot Inland Empire summer, a lower SHGC keeps afternoon rooms cooler. A Low-E coating and an argon fill both help. A west facing window needs a lower figure than a north facing one.

Visible transmittance

Visible transmittance, or VT, shows how much daylight passes through. A higher number means a brighter room. A window with a very low SHGC may also have a low VT, which makes the room darker, so the two numbers are read together rather than one at a time.

Air leakage

Air leakage measures how much air passes through the closed window. A lower number is better. A casement with compression seals usually tests lower than a slider, and a fixed picture window tests lowest of all because nothing moves. The figure only describes the window as tested, so the install still matters, and a unit with a good number can leak at the frame if the foam or sealant around it was skipped.

Using the label at the counter

The label is checked against the energy limits for the climate zone before a window is ordered. A unit that falls outside them cannot be installed in a permitted job. Comparing three or four labels side by side shows how much real difference exists between models that look alike on paper. Sun exposure around the Shandin Hills and Arrowhead Springs differs from the flat valley floor, so the same window can need a different SHGC target from one street to the next, and the label lets that be settled with numbers instead of opinion. The sticker is also photographed before it is removed and filed with the job papers.