Homeowner's Guide

Energy Efficiency

What is an air infiltration rate, and what should I look for?

TIP: Great Lakes casement windows have an even lower air infiltration rate — 0.012 (compared with an 0.098 rate for double-hung windows). Choosing a window style with lower air infiltration may benefit people with allergies or who live in industrial zones with higher environmental pollutant levels.

The Air infiltration rate is a measurement of the amount of air that can pass through a window. Air infiltration rates are set by certifying organizations and are verified by independent test laboratories and reflect reflect the amount of air that passes through a closed window. The lower the air inflation rate, the more comfortable your home (fewer or no drafts) and the lower your fuel bill.

Look for windows with thick, multi-layer weather stripping and fusion welded corners; they're better able to stop drafts and eliminate potential leaks. Also be sure any windows you buy meet current industry standards for air infiltration. Today's minimum property standard is 0.375. Great Lakes double-hung windows are rated at 0.098.

Are Great Lakes Windows ENERGY STAR Qualified?

Yes, Our Low-E glass system has earned ENERGY STAR qualification for all regions of the United States. ENERGY STAR is a voluntary partnership between the U.S. Department of Energy and window manufacturers. ENERGY STAR qualification should be one of the factors you consider when choosing a preplacement window.


ENERGY STAR qualification is based on NFRC certified product ratings.

What is a U-factor? Can it help me choose a better window?

Heat loss

The U-factor is a standard measure of heat transfer through an entire window unit. The methods for measuring U-factor ratings were developed by the National Fenestration Rating Council (NFRC) at the request of the U.S. Department of Energy and the Federal Trade Commission.

The lower the U-factor, the better the window's insulating ability. (A window's U-factor is the reciprocal of it's R-factor. Look fow windows with low U-factors and high R-values. See "R-factors.")

What is an R-factor and how is it important?

"R" stands for resistance. The higher the R-factor, the greater the amount of insulation a window provides. The R-factor rating of a window frame and glass is very important since it dorectly affects the cost of heating and cooling your home.

What are the R-factors for various window frames, and what is considered acceptable?

The following chart shows you the R-factors of different materials. The higher the R-factor, the better the energy efficiency. And as with any measure of energy efficiency, it's not so much what's considered acceptable, as what's acceptable for you. We fill every window frame with patented* R-Core® (pre-expanded high-density solid polyurethane insulation). The same type of insulation used in may refrigerator/freezer doors.

Our process of utilizing the pre-expanded insulation eliminates voids and settling that can reduce the effectiveness of other insulating methods. Our process increases the per linear inch R-factor from less than one to 7.14. If you want maximum energy efficiency, it makes sense to choose the window frame filled with pre-expanded high density solid polyurethane insulation.

*U.S. Patent Number 4,516,356

R-factor Chart showing the benefit of R-Core over other materials
R-factor Comparison of Various Window Frames (Per linear inch)

What is "warm edge" technology and how doeas it affect thermal efficiency?

"Warm edge" technology gives windows the strongest, longest-lasting and most thermally efficient insulated glass available. The Intercept™ process, the most state-of-the-art insulated glass spacer system available, is standard with most Great Lakes Window products. It's an insulated spacer system using a one-piece U-shaped channel to maintain consistent space between two panes of glass. This U-shaped system reduces the transfer of heat and cold and makes the entire unit stronger and more energy-efficient. And, unlike many of the most popular insulated spacer systems, Intercept passes the critical Moisture Vapor Transmission Rate test... which means the gas inside the window's insulated glass unit will stay in, and moisture that fogs the glass will stay out.

Is all window glass the same?

Definitely not. Glass available in a variety of types and colors including clear, gray, bronze, obscure and Low-emissivity (Low-E).

Glass is rated in R-factors too- the same used to rare window frames. They type of glass, thickness, number of panes, distance between panes, as well as, the manner in which panes are connected, all affect the R-factor performance of the window.

Is all Low-E glass the same?

Definitely not. There are two major types of Low-E glass: hard-coat (tin/prolytic) and vacuum-deposition (silver/sputter). Both types block radiant heat, keeping the summer's heat outside and winter's heat inside. And both block the sun's rays to some degree. But the similarities end there.

We recommend you look for windows with multi-layer vacuum-deposition Low-E glass for several reasons. First, silver based Low-E glass has better visual clarity. In fact, silver based Low-E has a "haze factor" of 0.14 - that's the same as plain glass. The haze factor for pyrolytic Low-E glass can be as high as 1.40. A haze increase of up to 1000%. With silver based Low-E, you get almost the same clarity as clear, 'uncoated' glass.

More important, our multi-layer Hi R+Plus soft coat Low-E insulates a minimum of 36% better than hard-coat (see the following chart).

R-factor Chart showing the benefit of R-Core over other materials
Glass R-factor Comparison
Figures are based on computer simulations performed by ATI in accordance with NFRC 100-97

Why do you use exotic gases in your insulated glass units, and are these gases safe?

We replace the air between the panes of insulating glass with high-density Argon gas. This process provides windows with both increase energy-effiency and increased sound deadening properties. Yes, Argon is safe, odorless, colorless gas that occurs naturally in our atmosphere - in fact, you are breathing small amounts right now. But because of it's density, heat and cold do not pass through Argon gas as easily as through air. As the cart shows, when Argon gas is used in an insulated glass system with soft-coat Low-E glass (like Great Lakes Window's Hi R+Plus), it's one of the most energy efficient windows you can buy.

Can the right glass really reduce furniture and carpet fading?

Definitely. Ultraviolet rays are one of the best-known causes of fading. Certain types of window glass can reduce the amount of UV rays that pass through the glass. For example, soft-coat Low-E glass with argon (Hi R+Plus) blocks 64% of ultraviolet rays - a 42% reduction compared to clear window glass.

but research has shown that factors beyond ultraviolet light contribute to fading and damage. So the usual tests for UV transmission may not give you the whole picture. (Besides, UV rays aren't all bad, plants need a certain amount of UV light to thrive.)

A more accurate estimate of fading protection is called the Krochmann Damage Function. This method, expressed in percentages, measures the amount of all damaging radiation (ultraviolet, infrared, visible light, and heat) transmitted through window glass. The Hi R+Plus system transmits as little as 16: of UV rays and has a Krochmann function of 22%. Conversely, teest Pyrolitic Low-D products showed transmissions as high as 47%, with Krochmann percentages as high as 52%.

I prefer humidity over dryness in my home. Can I reduce or eliminate condensation on my windows without reducing the humidity level?

Condensation usually occurs on windows because glass surfaces have the lowest temperature of any of the interior surfaces of your home. Using glass with the highest R-factors available, such as our Hi R+Plus systems, will not only keep the inside pane warmer to the touch, but will allow you to maintain higher humidity levels in your home.

I want windows that will help eliminate the noise from outside. Is there such a thing?

Certainly. In fact, the same features that make a window more energy efficient also help cut down on noise transmission from outdoors. The type of window glazing, overall insulated glass thickness and gas fill play an integral role in reducing noise transmission from outdoors. So not only are our windows with Hi R+Plus glass energy efficient, but they ma further reduce the ouside noise and hubbub.

Next Section — Window Features

This guide is provided as a service of Great Lakes Windows, Inc., to help consumers make informed buying decisions.