How to Read Energy Efficiency Labelling on Replacement Windows

At Clearwater Exteriors, we help our clients understand replacement windows every day. We often get asked about the energy efficiency labeling, energy star ratings, and how to understand what you are putting in your home when you do a window replacement project. This blog is intended to help you better understand the stickers you see on the replacement windows.

Energy Star and the ratings you see on the stickers were determined by an outside rating system. Manufacturers do not decide or lobby to get the rating you see. It must be earned on every product. Energy Star is an overall rating that is earned by exceptional energy efficiency. However, each number you see on the sticker is based on numerous tests that are done by the NFRC, not the supplier or the manufacturer.

   Let’s walk through the 4 blocks briefly:

 Energy Performance Ratings:
U-Factor: how good is the window at keeping heat inside? Lower is     better at keeping heat inside. Most windows fall between .15 and 1.2.
Solar Heat Gain Coefficient (SHGC): Measures how much heat from the     sun is blocked. Windows will fall 0-1, and lower is a better block to the         sun’s heat.

 Additional Performance Ratings:

   Energy Efficiency Label

Visible Transmittance: Measures how much light comes through, and is measured 0-1. Closer to 1 is more daylight.
Air Leakage: Measures how much air can come through the replacement window. This is generally between 0.1-0.3. Lower numbers imply less air can come through the window.

Aside from the Energy Star rating and the energy efficiency measures, there may be other considerations when purchasing replacement windows. This could include security performance, acoustic performance, water protection, structural requirements, and warranty considerations.