What is Low E Glass? What does it do? Do I need it? Are there any differences in Low E Glasses?

Low E glass is a piece of glass with a nearly invisible coating on one surface. If you can imagine molecular sized mirrors scattered randomly but evenly on the surface of the glass, you’ll be able to understand how it works. Break light into three sections. These are short wave, intermediate wave and long wave. Long wave is also know as “infra-red” and is already heat. As long wave tries to pass through the glass it will most likely hit a “mirror” on the Low E coated surface and bounce back because it is too big to slide between the mirrors. This is how Low E keeps existing heat from escaping through the glass. Short wave is also known as “Ultra Violet” or UV for short. UV is the light you need in order to see, so it is critical that it passes through the glass. The mirrors are far enough apart that enough UV travels through the glass, missing the mirrors because of UV’s small size, that you see comfortably through the coated glass.

Now for the difference between types of Low E glass! Sometimes Low E coatings are referred to because of different manufacturing processes. A “hardcoat” means that the coating was applied to the glass as the glass was being manufactured and was still in a relatively molten state. As a result, the coating is imbedded in the glass. This is what makes it harder than “softcoat” Low E Soft coat is sprayed on the glass after the glass manufacturing process is completed. Because it is on the glass surface without the bonding of hardcoat, manufacturers must use greater care in handling the glass. For the homeowner, these terms are actually useless because they don’t tell you anything about what the glasses do differently!

Now for the difference between types of Low E glass! Call the different Low E types “Solar Gain” and “Solar Shield” and things will start to make sense. In Solar Gain glass, the mirrors are slightly farther apart than in Solar Shield type glass. The result is that the two glasses treat the third size of light wave differently.  The third glass is the “intermediate” wavelength. More intermediate wave light can slip between the mirrors in a Solar Gain type Low E than in a Solar Shield, whose mirrors are close enough together to bounce back much of the intermediate light.

Keep in mind that any intermediate light that enters your home will turn into and be reradiated as long wave radiation when it touches your furniture, etc. You might say that it is the warmth on your face when you stand in front of a window receiving sunlight! So, Solar Gain glass benefits more than Solar Shield in utilizing free heat from the sun. On the other hand, Solar Shield glass limits the sun’s heat inside your home and allows your home to be cooler. it all comes down to you. In a Cold climate, generally you have many more heating days than cooling days, so one would tend toward Solar gain glass. However, individuals needs and concerns vary, so you may be more concerned with cooling issues and comfort than with a slight savings on heat. Both Low E glass types are so much better than regular uncoated glass that the difference is not earth shattering!

The differences in the two glass types can be seen in the technical numbers used to evaluate glass and this can sometimes be deceiving. If you look at the insulating value of glass as expressed in either a U-value or an R-value, you will easily see that Solar Shield has a better rating. This is because U and R are ratings of the amount of radiation that passes through a material and limiting more intermediate light from passing through the glass means that the glass means less radiation and a better insulating value. On the other hand, we have a term often presented as the initials SHGC. This stands for solar heat gain coefficient. it is a measure of free solar heat and in this rating, the Solar Gain glass is designed to out perform. In Canada we have a rating system called the E.R. or Energy Rating (described elsewhere in this FAQ). Because SHGC contributes to the E.R. number, identical windows except for Low E type will have a different rating with windows with Solar Gain glass having a significantly higher E.R. beware the salesman who says that one Low E is, “better”. They are different and what is better for one homeowner, may not be better for another!

What is Argon? Some contractors say not to bother and others say it is essential!

Argon is an inert gas commonly used to fill the inside of your sealed unit. What? There is some strange, exotic gas in my windows! What if it leaks out? Will it poison my family….

Inert means that the gas does not interact. In this regard it is a lot like nitrogen that makes up the bulk of the air we breathe. In fact, argon is in the air around you. In other words, It is harmless. Argon complements Low E in controlling heat loss through your windows because it deals with a different type of heat loss. In the Low E section of this FAQ we discussed how Low E affects light, which is a form of radiation. Argon affects the two processes of “conduction” and “convection”.

Let’s look at conduction on an atomic level! Let’s say that one atom is really hot and it is next to an atom that is really cold. There is a natural tendency for the level of heat to transfer between them and equalize, moving heat energy to the colder atom. This process continues atom to atom to atom, with heat being added into the chain of atoms from the warmer side. Over time, heat effectively leaves the warm side of glass to the cold side through this atom-to-atom conduction process.

Now let’s consider convection.  Convection is the movement of air currents in a circular motion.

We’ve all heard the expression that heat rises. This is because heated air expands and is lighter than colder air. Hot air balloonists count on this to keep from crashing into the ground! Picture the air inside a sealed unit. On the hot side of the windows the air adjacent to the glass warms up and rises. On the cold side of the window, the opposite happens and the air is losing heat, gets heavier and drops. This creates a rotating current inside the sealed unit. As the warm air drops, it is pushed to the cold glass side where it transfers some of its heat to the cold glass and beyond. The same happens on the other side where the cold air picks up heat from the glass and continues to rise.

Argon has different physical characteristics than regular air and these characteristics slow down both heat transfer and a molecular level (conduction) and from convection. Argon is a fantastic complement to Low in is a sealed unit with 1/2″ to 5/8″ air space.

Krypton is very expensive. If Argon is good, Krypton must be better, right?

If by better you are only looking at performance numbers, yes, krypton is better. A more important question is, how much better? In a sealed unit with 1/2″ to 5/8″ air space, while krypton is better, it certainly is not “better enough” to justify the difference in cost. Payback takes longer then the life of a typical thermal glass!  On the other hand, argon is relatively ineffective in smaller air spaces and krypton excels! The best use for triple is in an 1/4″ air spaces such as you would find in a triple thermal unit that is part of a sliding window system. (Note that OLYMPIA casement, awning, fixed and picture windows use sealed units with two 1/2″ air spaces for triple, so argon, which is very economical, does the job as well as krypton in the two 1/4″ air spaces!)

What is a "U" value? "R" value? E.R? Is E.R. the same as "R"?

Engineers do love their numbers! A definition of “U” value is that it is a measure of the rate of heat conductivity of a glazing system. The “R” value is a measure of thermal resistance. Now let’s forget the engineers and try to make thing simple. They are both measuring the same thing from opposite perspectives. “U” measures the rate of heat transfer and “R’ measures the rate of resistance to heat transfer. So, the formula is: R x U = 1

For example, if you have a window that is R5, then the U value of the window is .2. (5 x .2 = 1 as per the above formula.)

The higher the “R” the more resistance the window has to losing heat. The lower the “U” the less heat is moving through the window (and therefore lost).

Now, in Canada we use metric numbers and an even less familiar number is the metric U value. Like “R” value, the metric U is higher when a material has better insulating characteristics.

The E.R. number is another performance measure with a troubled past that can make it especially confusing for homeowners trying to compare windows. When introduced in the mid 1980s, the system was designed for the number 0 to mean that a window was gaining as much solar heat as it was loosing through glass, framing materials and radiation. The problem was that homeowners didn’t understand that they were primarily looking at negative numbers so they often thought a -21 was better than a -7 because they missed the minus sign!

To correct these types of misconceptions, the system was move approximately 34 points (not exactly) into positive numbers so a window that was once -28 might now be +6 and a window that was -4 might now be +30. “U” and “R” value are only measuring heat transfer through the materials. E.R. measures this but also measures loss from air infiltration as well as heat gain from solar heat.

ENERGY STAR rates windows with an E.R. number? But, what does it really mean?

Let’s start with the formula they use to create it.

E.R. = (57.76 x SHGC) – (21.90 x Uw) – (0.54xL75) + 40

And now the breakdown…

57.76 = An average factor to account for shading of the sun

You remember that salesman who sat at your kitchen table and told you not to use the E.R. system because it didn’t account for shading of the sun’s heat over the course of the year? This is the factor used to take that shading into account. Another aspect of shade is that the sun is lower in the sky in winter. In summer, when you don’t want the heat, more is shaded by your roof and overhangs. Also, many of the shade providing trees around your home help cut air conditioning costs in summer, but when they lose their leaves in winter, allow the sun’s rays straight through your windows!

SHGC = Solar Heat Gain Coefficient

The percentage of available solar heat that will make it through the glazing, taking into account how much of the window design is glass vs framing materials.

21.90 =   A heat transfer temperature factor (average indoor/outdoor temperature during heating   season)

Heat moves from warm to cold. Looking at our extended heating season (September to April?) this factor assumes that heat is constantly trying to achieve temperature equilibrium.

Uw =    U factor – a measure of heat loss in watts per minute

The rate that heat is moving toward equilibrium.

.54 =    A pressure reduction factor

Air leakage is a result of the different pressure inside and outside. This is a factor to average out heat lost through air leakage. Note that I am not saying penetration because, while there is pressure equalization, there is also what i will call “flow through”, so there are spots in your home where air is leaking in and spots where it is leaking out.

L75 =   A measure of air leakage

Used with the pressure-reducing factor to measure the value of heat lost by air leakage.

40 =     A factor to make all numbers positive!

When the E.R. system was created, the idea was that an E.R. of 0 (zero) meant that the amount of solar heat gained in heating season equaled the amount of heat lost through the window. At that time a positive number meant that the window was actually gaining more heat than it was losing! Of course, most windows had negative numbers.

Scientifically, this was the correct way to go, but practically it didn’t work. Homeowners had a hard time realizing (and in some case may have been intentionally misled) that a -5 was a better performer than a -25. The tendency was to see the negative sign as simple a placeholder. 25 has to be better than 5, right?

After some years of confusion, the decision was to add +40 to every number to push the ratings into the positives. Our -5 becomes +35 and -25 becomes +15. 35 really is better than 25, so it is harder to misunderstand the numbers. It is certainly possible for a sales person to be walking around with very old brochure materials that have negative numbers. Don’t be fooled by this tactic!

Why does a window with a better "U" value compared to another window have a worse E.R. rating?

Some windows are designed to maximize “U” and some to maximize E.R.  This is done through the use of different types of Low E glass as discussed elsewhere in this FAQ!

What does it mean to "tune your home"?

Tuning your home refers to a practice of choosing different Low E coating types for the different sides of your home. OLYMPIA offers both “hardcoat” Low E and “softcoat” Low E to help homeowners achieve best results.

What is the difference between a CSA tested window and a CSA Certified Window?

CSA stands for Canadian Standards Association. This organization is charged with maintaining standards for how products are tested, among many other responsibilities. In the Window industry, CSA maintains a standard called the CSA-A-440. This standard specifies how a window can be tested so that all window companies can be judged on a level playing field. Any company can test a window to this standard. Generally, only tests performed at certified laboratories are considered to be of value.

Even when a window is independently tested, there still can be problems if the manufacturer changes the materials and methods of how they manufacture their windows. A change can result in a degradation of performance as easily as an improvement, so a test should only be considered valid when the product manufactured is exactly the same.

Then the question becomes, how do you tell if the tested product and the manufactured product are the same? This is the difference between a product tested to the CSA-A-440 and a product Certified to the same standard. When a product is certified by CSA, it means that they have monitored how it is made and its components to assure that at the time of the test, what was tested was a production model. Then, over time, CSA continues to monitor production to assure that it has not substantially changed.

How can the same window be ENERGY STAR qualified and not ENERGY STAR qualified?

This is a question with two answers. The first is, there are certain energy related options that will vary the performance of a window. A window without Low E and Argon may be the same model as one that has these two options, but it does not have the same performance level. The same model without the energy improving options may not be ENERGY STAR qualified, while with them, it is.

The second part of this question really refers to testing. A window model with triple glass, including two coating of low e and krypton gas is probably a great window and could easily meet an ENERGY STAR standard. But, if it hasn’t actually been tested with that exact glass package, then it doesn’t qualify due to lack of paperwork. Many great windows are not tested because not enough consumers want that exact package to justify the cost of the testing.

Which is better, painted or co-extruded exterior colour?

This is not an easy question to answer. It can depend on the quality of the pigments in either method of colouring a window. The darker the colour of a window, painted or co extruded, the more of the sun’s radiation is being absorbed. Remember, seeing something white means the object is reflecting the full spectrum of light. Seeing it black means it is absorbing it. That is why darker colours tend to create heat inside, as the absorbed radiation is reradiated as long wave infrared

Modern paints used in the window industry actually have a heat reflecting property. In fact, there are interior house paints now on the market that are promoted as reflecting heat back into the room. Sounds like the same type of paint!

Manufacturers of resins for co extruding readily agree that fading was a problem in the earlier days of the vinyl window industry. They are also quick to say that today’s pigments and resins are much better at fighting fade and are the equal of painted products.

Your choice may come down to availability as co extruded material tends to be available in less dark, more popular colours. Painting can be done in lower quantities and often is available in a wider selection of standard and even custom colours.

Will new windows solve my condensation problem?

Condensation is the result of any surface, glass or otherwise, being cold enough to cool the air it contacts below the point where the air can maintain the moisture content it carries.

If we assume that in replacing your windows, the surface of the interior of the new windows is better insulated than the old windows, so therefore the surface temperature of the new window is also warmer.  All else being equal, you can expect reduced or eliminated condensation, but, all else is not equal. When you change your windows you are probably sealing your home from losing heat through air escaping from the home. Since the air you used to lose was moist, this tended to reduce the moisture content of the air in your home. Now, with new windows, the moist air stays in the home. The moisture content of the home’s air rises. It is possible for the condensation to be worse than before, if the humidity level in the air is too high, even though the window itself is warmer.

Don’t panic! This proves that your windows are doing what you paid for, which is, sealing your home. You will need to find ways of removing the moisture from the air. There are many documents on how to reduce or eliminate condensation available on line, as well as on our Links page.

I do want to mention that, in addition to reducing condensation, preventing the area around your window from becoming a refrigerator in an otherwise warm room is another important part of reducing or eliminating condensation. Heavy curtains, too close to the window, that prevent air circulation, prevent the window from receiving its share of warmer air available in the room. Make sure the air adjacent to the window is able to move reasonably freely and exchange itself with the rest of the air in the room.

Which window operator style is better?

This is a simple enough question. Unfortunately, there is no simple answer. Better for what? If the only issue is, for example air, water or structural performance, then usually a casement or awning is the better performer than any sliding window. This is simply because it seals by compression. Sliding windows need to be loose enough to move when shut.

The simple answer above doesn’t take into account the architectural design of your home, nor does it take into account the size of the openings into which you are putting windows. Some homes simply look better with a particular style of windows. Some openings are of a size or shape where a particular style of operator is not practical. The choice may be between two operators on one style or a single window of an alternative.

Should you worry overly about not being able to use the “tightest” window in a particular location? Even sliding windows can have excellent ratings. I am being simplistic from an engineering point of view, but most homeowners would not be able to notice a difference on their heating bill from a great A2 window to a typical A3 window. (A being the CSA system of measuring air infiltration in three steps, from A1 to A3.)

I do recommend paying closer attention to water penetration than air infiltration in the decision making process. If you live on a cliff with wind driven rains, you may prudently decide not to put in a panoramic, big horizontal sliding window and instead, choose to use casements or awnings combined with fixed windows for their superior performance resisting water penetration. Where air infiltration can be an inconvenience, water penetration can result in consequential damage to your home.

Back to the original question, we can see that there are trade-offs between window styles regarding differences in performance, the look and viability in a given opening. In deciding what to purchase, make your decision based on taking into account what will overall be in your long-term best interest and not ignoring all but one of the pertinent issues!

The glass is broken in my window. Does this mean I need to replace the entire window?

I can’t imagine any company making a window where the glass cannot be changed. There are too many small children, playing ball, to assume nothing will ever happen to a pane of glass! That being said, there have been times when operating sashes in some windows were made in a way that they needed to be completely replaced when changing the glass, but these are, happily, a real rarity and unless you are the type to get hit repeatedly by lightning, probably not in your windows.

I would question anyone who tells you that glass, including a sealed unit, cannot be replaced. On the other hand, depending on the age and quality of the window in question, it may be a better use of your limited home repair budget to replace the whole window if the result is going to drastically improve the energy efficiency of the window.

How much savings can I expect from this new window?

A homeowner, whose home had 15 windows, was planning on changing one window and asked the sales person who much savings he could expect when the change was made. The salesperson replied, “None.” The homeowner was shocked and asked the sales person, how can you say this? You just told me that this was a highly efficient new window and my old window is a piece of junk! The sales person calmly answered, “You can’t expect a noticeable improvement when the other 14 windows are still leaking massive amounts of heat!”

The sales person in the above is absolutely correct. Don’t expect miracles from a single change. You must begin to think of your home as in interlocking system. Insulation (including windows and doors), heating and cooling and air flow within the home all need to work together efficiently.

If one of these areas is out of balance with the others, your home may have many energy efficient components, but the result will not be the best it could be.

Another example to illustrate this is the building manager who replaced a six story apartment building’s single glazed windows with new, high efficiency windows and who called me asking why his heating bill that winter continued to be high. The two of us stood outside the building in freezing cold and stared at the building. The answer was obvious. Half the windows in the building were open because the buildings central thermostat system had not been adjusted for the fact that the apartments were now naturally warmer through retained heat. Renters had the windows wide open because they were getting too much heat from centrally controlled utilities.

Changing one window at a time is often practical from a budgetary point of view, but it is very hard for the homeowner to see the expected savings until the home’s overall efficiencies rise more significantly then from a single window.

My new windows are not as quiet as my old windows! How can this be?

This is not common, but is possible. In most cases, homeowners are going from badly sealed windows, which leak noise from the outdoors into your home, to new windows with tighter seals that result in less noise getting it. if all other factors remain relatively the same, this is the most likely scenario.

The key is, whether or not all factors remain the same. If your old window, with a wood storm for example, had been painted shut, it would be as tight as your new window, just not functional and probably not energy efficient. On the other hand, the air space between the single glazed inner window and the outer storm could be 3″ or more. This gap between the glasses is not energy efficient, but it is sound efficient. All factors being the same and going from a 3″ space to a space that is less than 1″ between the panes will result in increased sound transmission.

In addition to larger air spaces, sealed units with offset thicknesses of glass are quieter than sealed units where all lites of glass are the same thickness because sound frequency filtering in each glass varies depending on the thickness. Your window filters a wider range of frequencies when the lites of glass are targeting different frequencies. At the higher end, laminated glass tends to diffuse sound and is very effective at noise reduction through a window.

How do I convert a Metric U value to an old fashion R value?

This is a two-stage operation and we’ll use an example.

One Imperial U equals 5.678 metric U.

Take a window with a metric U of 1.55

Divide by 5.678 = .273

.273 is the Imperial U value.

Imperial U times Metric U equals 1, or divide 1 by either to get the other!

1 divided by .273 = 3.66

In this example, a window with a Metric U value of 1.55 has an R value of 3.66!

I was told you can tell the quality of vinyl on windows by the colour. Is this true?

Unfortunately, sales people who were “educated” to believe this urban myth sometime perpetuate this myth. As well, some choose to believe it as a means of justifying and promoting the colour white vinyl they have to sell. Often the sales people with the bluer white justify it by saying you are seeing high quantities of titanium dioxide, which is the chemical used to resist UV degradation. There are salespeople selling the neutral white who will say that the bluer white gets its colour from too much calcium carbonate, which is a filler material. Both are false statements. Both the bright (bluer) vinyl and antique (neutral) vinyl can be made using state of the art compounds. The colour is just that… a colour. The truth is, no major extruder is using a significantly inferior quality PVC vinyl.

We normally use what we call the OLYMPIA white (neutral white) because we find it looks exactly “neutral” and matches inside-outside better than the “blue white”, but we can also offer  the “blue white” if customer prefers it.

A competitor said he has windows that exceeded R8!, even as high as R10! About your windows?

In the window industry, when comparing glass, it is common to compare the R values of the glass only, using a measure called “centre-of-glass” This is where the R8 exists, generally only in triple glazed windows. An R8 centre-of-glass is independent of the choice of window style you may make.  Once you put this (or any other glass) into a window, that window then has an overall R value that is different (and lower!)

Canadian Standards Association do not look at glass in isolation of a window. The glass with the R8 centre-of-glass is a triple with double softcoat Low E and a gas fill.

Of course, as noted earlier in this FAQ, there is a big difference in the performance you can expect from a triple glazed unit that has an overall thickness of 7/8″ and one where the overall thickness is 1 3/8″. Most of our competitors can only have 7/8″ overall thickness glass in their windows. (They can make a thicker glass, but can’t actually use it in the windows they have on the market!)

Our casements, awnings, fixed and picture windows can all utilize a 1 3/8″ glass! This means that the R8+ centre-of-glass can be achieved with inexpensive Argon gas. If you are offered a window with 7/8″ overall glass thickness, it has to have krypton gas fill to achieve R8+ centre-of-glass.

In other words, OLYMPIA can offer a cost effective R8+ centre-of-glass!

Do I need to pay extra for a "foam insulated" window? Is it cost effective?

I prefer the term “foam insulated” to foam filled. I’ve never seen a production window that is completed filled. The answer to this question is a matter of cost/benefit. if you are on a fixed retirement income your “cost”, even though the dollar value is the same, is much higher when compared to someone with money to burn.

For you and your budget, the benefit may not be justified by the marginal cost. Low E and argon gas fill are probably the cheapest bang for your buck in window upgrades. The next option you add will likely have a lesser benefit for a higher cost. Foam insulation is no exception. There are companies that will try to justify exorbitant price differences based on the inclusion of foam. It isn’t that expensive, so get legitimate quotes!

In a badly designed window, foam can add significantly to the frame and sashes insulation potential. In a well-designed window, it will still have a benefit, but not as much. You can add +2 E.R. points to a well-designed and well-constructed window as the benefit that will result from properly installed insulating foam.

OLYMPIA offers foam insulated windows for those customers that feel they need it.