Window, Door and Skylight Energy Performance Ratings

Here at Baltic Home Improvements, we have more than a decade of experience with installing windowsdoors and skylights. We recommend and use only high-quality products that have good energy performance ratings but many people do not fully understand what is revealed by these ratings.

The US Department of Energy recently posted a very useful guide to understanding the Energy Performance Ratings for Windows, Doors and Skylights. These ratings can help you determine how these home improvement items can affect the energy costs associated with running your home.

The article explains how the National Fenestration Rating Council (NFRC) conducts tests and certifies these home features and then labels them with energy performance ratings with an ENERGY STAR® tag. Some things that the NFRC tests for include:

Heat gain and loss in terms of

  • U-factor: this is the rate at which the window, door or skylight conducts non-solar heat flow. The lower the U-factor, the better.
  • Solar heat gain coefficient (SHGC): this is the amount of solar radiation that the window, door or skylight releases into the home. The lower the SHGC, the better is it as keeping the interior of your home cool. The higher it is, the better warmer your house will be – which may be a good thing during a cold Chicago winter.
  • Air leakage: this indicates the amount of air movement in and around the window, door or skylight and is indicated in units  of cubic feet per minute (cfm/ft2). In this case, the lower the rating, the better.

Sunlight transmittance in terms of:

  • Visible transmittance (VT): this is the fraction of visible sunlight that is transmitted through the window, door or skylight. The higher the VT (which is expressed as a number between 0 and 1) the more well-lit your home’s interior will be by the sunlight.
  • Light-to-solar gain (LSG): this is the ratio between the SHGC and the VT. The higher the number, the more light you can have in your home without excessive heat. The article points out that this rating is not always provided.

For more information, be sure to read the full article which can be found at Energy.gov.

Image Source: Leo