The Truth About Windows

I can’t tell you how many times I’ve met with homeowners only to hear that they had replaced all their windows with energy efficient windows and they just couldn’t understand why they weren’t saving any money. The truth is, every window manufacturer wants you to believe that putting more energy efficient windows in your home is going to save you tons of money. Well it’s not! You can argue with me all you want, but if you have ever heard Charlie Wing talk about single pane windows you would know that you aren’t getting all the information you need to make an educated decision on upgrading the windows in your home. So let’s talk a little bit about why upgrading the windows in your home is one of the last things on my list of energy improvement recommendations.

First things first, they are expensive. Rarely does a window replacement pay for itself before the end of the useful life of the window, which is often 20-25 years! If you haven’t read my previous blog post about R-value I suggest you do that now before you continue with this article.

Windows are just one part of a system that we call the “envelope” of your home. The envelope consists of walls, windows, doors, roof, and some type of flooring in the way of dirt, concrete, rock, or other foundation material. According to the US Department of Energy, 14% of energy is going through the envelop of buildings.

Like every architect, I know the value of a well-placed window that provides scale, dimension, light, and style to a building. All human beings crave light, and want to be able to see out from their homes. But replacing the double pane windows you have in your home isn’t going to save you the most money, even if they were installed more then 20 year ago. The hardest thing about energy improvements is that the stuff that makes the biggest difference is always the stuff you can’t see.

There are two types of heat loss. Air transported heat loss (how drafty your house is) and surface transported heat loss (how well insulated your house is). Windows actually fall into both categories. Homeowners often tell me they want to replace their windows because they are drafty or old. Well it may not be the window itself that is drafty, but the way it is installed. The biggest difference most homeowners see with a window replacement is in the installation. Contractors are now caulking around the windows, reducing airflow, and creating a much tighter building envelope. We no longer stuff fiberglass around the shims in windows because we know it just filters the air coming in, it doesn’t stop it. Old single pane windows with counter weights are just large open channels for exterior air to enter the home. So if you have windows with counter weights it’s in your best interest to replace them. If the window has failed and has condensation inside, it’s best to replace it. But if you have double hung windows, in decent shape, upgrading to newer windows should be the last item on your list of home improvements.

The standard double pane window has an R-value of 2. Some of the best, readily available, windows on the market have an R-value of 5. This is excluding windows specifically made for passive house applications, which can have higher R-values, but also have much higher price tags. Windows are typically listed in U-value. U-value is the inverse of R-value and for the purpose of the example below we are going to use Maine. Maine is located in Zone 6, in the current 2009 Energy Code, adopted most places. The current requirement for new construction windows is U-0.35 or R- 2.9, hardly higher then the R-2 windows you currently have in your home, because they just don’t make glass you can see out of that has high insulating properties… yet.

Let’s look at an example. If I were to replace one 3′ x 5′ window, a fairly common size window, what would be the results? Let’s say the original window was a standard R-2 double pane window and I have decided to replace it with a new triple pane R-5 window. Just for reference the basic heat loss equation I used was (Area X Heating Degree Days X U-value X 24 hours a day). Without getting into heating degree days and what a British thermal unit (Btu) is, the information I got out of the calculation was that it would use 9.97 gallons of oil to heat the existing window in Mid-coast Maine for 1 year. It would use 3.98 gallons of oil to heat the new window for 1 year. And if you decided instead to upgrade your attic hatch, using the equivalent 15 square feet, to an R-49, it would use 0.38 gallons of oil per year. At an average of $3.50 per gallon that would be $35 for the exiting window, $4 for the new window, or $1.34 for the attic hatch. And you wonder why I throw in attic hatch? Well I bet, just like mine, yours doesn’t have any insulation, is not air sealed, and is either a piece of plywood or sheetrock painted to look the same color as the rest of the ceiling and costing you $35 per year to keep warm instead of $1.34!

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