You see advertisements all the time. Buy our window- it's the best. With the institution of Energy Codes and new labels that door and window manufactures must supply with their products, comes a way for you to compare the energy efficiency of doors and windows. These labels are somewhat like food labels describing what's in the food we consume. With doors and windows, standard testing methods are used to give consumers a way to compare one manufacturer with another. Of course, there is more than just the glass in a window or door. So making your decision is still a little more than just comparing stickers. You will also need to take into consideration accessories, colors, and options that fit your needs.
Let's get started on what all those number mean on the stickers. To the left is a sample like what you will see when purchasing doors and windows. Here are the terms and explanations of what they mean:
- R-Value is a term most of us know or at least heard of. Most insulation used in our walls and ceilings is based on its’ R-value. In case you don’t know R-value is the resistance a door window has to thermal transfer or heat flow. Expressed as a number such as R-3.1. So when it comes to R-values the higher the number is better.
- U-Value is the amount of heat transferred through a material. The lower the U-value, the slower the rate of heat flow and the better the insulating quality. So a low number U-value is good.
- Solar gain (also known as solar heat gain or passive solar gain) refers to the increase in temperature in a space, object or structure that results from solar radiation. The amount of solar gain increases with the strength of the sun, and with the ability of any intervening material to transmit or resist the radiation. Usually expressed as solar heat gain coefficient (SHGC)
Other factors increasing energy efficiencies are the number of panes, coatings and if gas is used between the glazing.
Double and triple pane is really self explanatory. Double pane has two panes of glass and triple has three panes of glass, each separated with an air space. Most windows I see installed are double pane with Low E glazing. Don’t get me wrong triple pane glass is very efficient. The problem is by adding the extra pane; it makes the window very heavy.
I am sure by now you have heard the term Low E. Low E stands for low emissivity. Low E glass has a transparent metallic coating applied to glass surface to separate heat energy (long wave) and light energy (short wave) – long wave is reflected back to the heat source and the short wave can pass through the coating. Any new window you install should be Low E, if you don’t your missing out on a relatively low cost benefit.
Yet another way manufactures increase energy efficiency is by adding a gas between the panes of glass. Typically this is done with argon or krypton. Argon has about has a 30% lower thermal conductivity than air. Typical methods is to place argon or krypton between the glass instead of air One problem is that these gasses are known to typically leak out about 1% per year. It really doesn't hurt the window or door as it is replaced by air, it's just that over time it can leak out.
So when you go shopping for new doors and windows. Don't be fooled by a great sales pitch. If you know your terms and what they mean you will be able to make the best of your purchase.