Window Design Elements

Home Builder with Green City Window and Door


Today there are many manufacturers of windows, which can cause difficulty to choose a quality product. Of course, most companies or window salesperson claim to have the best product. Window Replacement Everett Green City Window and Door

There are serveral design elements and options to look for when choosing your windows and professional installer. Some of the elements are listed below: Window Replacement Everett Green City Window and Door

  • IG Units: is the number of panes of inslated glass.
  • Low-E: "low emittance" coatings, which minimize thermal radiation (damaging rays).
  • Low Conductive Gass Filled: Argon or Krypton
  • U-Factor: heat loss rating
  • SHGC Factor: amount of solar radiation (heat) admitted through a window. 
  • VT: Visible Light Transmission

The following informatio will take some of the "mystery" out of window terms. Window Replacement Everett Green City Window and Door

IG Units: What is "IG" unit?

Today, quality windows are built around what's called an insulated glass (IG) unit. An insulated glass unit starts out as two or three individual panes of lgass that are chemically bonded by a sealant to spacer bars. When comparing vinyl replacement windows, always ask about the IG unit. Because not all windows or glass are alike, you should require the highest quality and performance standards. Window Replacement Everett Green City Window and Door

Low-E: Is it for me?

Low emittance (Low-E) coatings are thin, metal or metallic oxide layers deposited on a window surface primarily to reduce the U-factor by suppressing the heat flow through the glazed window unit. Coating the inner glass surface with a low-emittance material between the glass layers, with a low-emittance material between the glass layers, blocks a significant amount of this radiant heat transfer, which lowers the heat flow through the window. Low-E coatings are transparent to visible light. Different types of Low-E coatings have been designed to allow for high solar gain, moderate solar gain, or low solar gain. We usually recommend Low-E for any regions in your home that receive a lot of direct sunlight. One thing to remember is the windows have a slightly tinted appearance. Window Replacement Everett Green City Window and Door

Low Conductive Gas Filled Units:

An improvement that has been made to the insulating performance by the use of argon or krypton gas between the panes of glass. Normally the space is filled with air or dry nitrogen prior to sealing the window panes together. In a sealed glass insulated window unit, air currents between the two panes of glazing carry heat to the top of the unit and settle into cold pools at the bottom. Filling the space with a less conductive gas minimizes this and the overall transfer of heat between the inside and outside is reduced. Window Replacement Everett Green City Window and Door

Argon is inexpensive, nontoxic, non-reactive, clear and odorless. The optimal spacing for an argon- filled unit is the same as for ait, about 1/2-1 inch. Window Replacement Everett Green City Window and Door

Krypton has better thermal performance, but is more expensive to produce. Krypton is particularly useful when the space between glazing's must be thinner than normally desired, for example, 1/4 inch. A mixture of krypton and argon gases is also used as a compromise between thermal performance and cost. Window Replacement Everett Green City Window and Door

The use of conductive gas filled units has significant insulating benefits but comes at higher initial cost.

U-Factor- What exactly is it?

The rate of heat loss is indicated in terms of the U-factor (U-value) of a window assembly. The lower the U-value the greater a window's resistance to heat flow and the better its insulating value. Winter nighttime U-values are calculated using an outdoor air temperature of 0 degrees F and outdoor air velocity of 15mph, indoor air temperature of 70 degrees F, and air veolcity of 0mph. This is similar to the R-Rave that you think of when choosing insulation except a low U-factor is better, unlike R-value which the larger the number the better. Window Replacement Everett Green City Window and Door

It is calculated as 1 divided by the R-value=U-factor. If you used this calculation R-13 insulation would have a U-factor of 0.077.

To conver U-factor to R-value you take 1 divide by the U-factor. If you used this calculation for the average aluminum framed window ith a U-factor of 1.125, your R-value would be 0.89. Window Replacement Everett Green City Window and Door

Good replacement windows depending upon the glazing options and low conductive gas fills range between 0.5 and .10 for the U-factor. Window Replacement Everett Green City Window and Door

SHGC Factor- What is it?

Solar heat gian indicates the total amount of solar energy that passes through glass relative to a 1/8" (3mm) thick clear glass under the same design conditions. It includes both solar energy transmitted directly plus any absorbed solar energy subsequently re-radiated into the room. Lower values indicate better performace in reducing summer heat gain and, in turn, air conditioning loads. Your average single paned wood framed window has a SHGC of 0.98 whereas a quality replacement window will have ratings from 0.91-0.39 depending upon glazing options. Window Replacement Everett Green City Window and Door

VT- Visible Light Transmission:

The visible transmittance (VT) is an optical property that indicates the amount of visible light transmitted. The VT is a whole window rating and includes the impact of the frame, which does not transmit any visible light. While VT theoretically varies between 0 and 1, most values are between 0.3 and 0.8. The hight the VT, the more light is transmitted. A high VT is desirable to maximize daylight. Window Replacement Everett Green City Window and Door


I hope this article helped demystify the terms used when you are contemplting your new window replacement purchace. Purchasing a quality window is only a part of the equation. The installation is the largest factor of how your windows with perform. Take great care installing and insulating around your existing openings and windows to assure you receive the maximum performance possible from your windows.  Window Replacement Everett Green City Window and Door


For Window replacements from Green City Window & Door, call us at 425-200-9191 or e-mail us at


Sharon Parisi
United Real Estate Dallas - Dallas, TX
Dallas Homes

John, thank you for sharing this wonderful information about windows.  You've answered a lot of questions.

May 17, 2014 04:40 PM