Photo Credit: Heather Telford Photography


You’ve probably heard that energy-efficient windows are an effective way to reduce heating and cooling costs, but how do these windows actually work? And how do you know how effective an energy-efficient window will actually be?

How do energy-efficient windows work? Gas Fills

Energy-efficient windows are typically insulated glass units (IGUs) that are double- or triple-paned. The space between the two panes creates insulation between the outside and inside. To make this insulation space more effective, manufacturers of energy-efficient windows will often pump Argon or Krypton gasses into the space between the pains.

Argon is a non-toxic, inert, clear, and odorless gas with thermal conductivity of about 67%. This gas is more viscous than typical air, which means its convection currents (transfer of heat and cold) moves more slowly, reducing the transfer of heat across the window.

How do energy-efficient windows work?  Low-E Coating

Low-E coatings minimize the amount of ultraviolet and infrared light that can pass through the glass without compromising the transmission of visible light. Emissivity is the ability of a material to radiate energy, while low-emissivity (low-e) means a material transmits less ultraviolet and infrared light.

Low-E coatings work by adding a microscopically thin, clear layer that works as invisible microscopic shutters that reflect infrared energy away from the surface, reducing the radiant heat loss through the glass. These coatings can be on both the inside-facing and outside-facing panels of glass, keeping heat out during the summer and reflecting the indoor temperature back inside.

How do you measure energy-efficiency?

Most energy-efficient windows will have a number of different ratings, but what do they mean?


The U-Factor is the rate at which an insulated glass unit conducts non-solar heat flow. It’s typically expressed in units of Btu/hr-ft2oF. The lower the U-factor, the better the window’s insulating properties.

High-performance double-pane windows can have U-factors near 0.30, while some triple-pane windows can achieve U-factors as low as 0.15. Energy Star recommends u-factors for your climate here:

Solar Heat Gain Coefficient (SHGC)

The Solar Heat Gain Coefficient (SHGC) is the rating used to help measure the energy efficiency of windows, doors, and skylights. The SHGC rating quantifies the  percentage of incident solar radiation that enters the home directly or indirectly from the sun, sky, or heat reflected off of outdoor surfaces. Single-pane uncoated glass has an emissivity of .86 or 86%, while most Jones Paint & Glass windows have an SHGC of .21-.30.

Energy Star Rating

Energy Star Approved windows meet strict regional energy-efficiency requirements that are at least 40% more efficient than required by most common national building codes. Energy Star is the premier designation for energy-efficient products.

Do energy-efficient windows really save money?

Your savings will depend on your current windows as well as the windows with which you choose to replace them. The greatest savings amount will occur when going from single-pane windows to double- or triple-pane, Energy Star-rated windows, typically with low-e coatings and gas fills. However, depending on your current SHGC, most customers who make the switch to energy-efficient windows still see a dramatic decrease in their energy bills.

Energy efficient windows can save you on average $9.25 – $38.75/month on energy bills for a total average savings of between $111-465/year. This range is largely dependent on the windows you had before you replaced your windows with Energy Star Rated windows. If you have single-pane windows now, your savings will be much greater (closer to $465/year) than if you have double-pane windows (closer to $111/year).

Replacing your windows with more energy-efficient windows also immediately benefits your home value, recuperating over 74.2-74.7% of cost in home value, according to the 2018 Cost vs. Value Report.

Energy efficient windows, doors, and skylights, may also qualify for Federal Tax Credits. Stay up-to-date on the latest credits at

Do you have any questions about energy-efficient windows or would you like to schedule a free on-site quote? Call 1-855-415-6637.