Glass and windows play a big role in energy usage

May 19, 2022 – Did you know that 30 percent of the summer cooling costs in Southwest Florida are attributed to glass and windows? For those with tons of glass and windows in your dwelling, it is essential to understand the role that glass and windows play in allowing solar heat to enter your home in our summer-dominant climate.

All transfer of heat energy occurs as the result of convection, conduction or radiation:

Convection occurs when heat energy, embodied in a substance, usually air, moves from place to place as the embodying substance moves.

Conduction occurs when heat energy moves from molecule to molecule through a substance. The greater the difference in temperature, the greater the flow of conducted heat.

Radiation is the process by which most heat energy enters homes in Southwest Florida. Every object embodies or stores heat energy and some of this heat energy leaks away in the form of infrared radiation or radiant heat.

Along with understanding how heat enters our home, LCEC energy experts suggest the following tips to stay cool while keeping your electric usage under control:

  • Significant air-conditioning savings can be attained by blocking solar heat before it reaches the windows, or by using special heat-reflecting glass or heat-reflecting glass coatings (residential window tint).
  • Reflective glass or reflective glass coatings should be rated to reflect at least 65 percent of all solar heat to be considered efficient in Southwest Florida.
  • Internal window coverings trap solar heat between them and the window glass until the heat energy warms the air in that space. The heat-laden air flows up to the ceiling, where it waits for the air conditioner to cycle on and draw it in through the filter. This creates an illusion of efficiency when, in fact, the load on the air conditioner has not been altered.
  • Awnings, storm shutters, shade trees and porch or lanai roofs are all very effective in blocking solar heat. To be 100 percent effective, the exterior shading device must never allow direct sunlight to touch the window’s surface.
  • East or west windows are the main source of intrusive heat. It is recommended to use shading devices and tint on east and west windows since they experience many hours of direct sunlight.
  • South-facing windows experience a great deal of direct sunlight in the winter months when the sun rides lower in the sky. In the summer, south-facing windows are largely shaded by the overhanging soffit of the roof.
  • Skylights experience many more hours of direct sunlight than any vertical window and should be avoided if possible.
  • It is difficult to utilize shading devices to block the sun from entering skylights. Existing skylights can be tinted, covered, blocked or shaded to lessen their load on the air conditioner.
  • When upgrading windows, consider energy-efficient features such as double-pane, low-E glass as well as type of frame material.

Visit for more ways to save on your energy consumption!