I read somewhere that the best performing window is called a wall...

Of the many products or materials I've considered for use in this house, the windows presented several unique challenges. Most people overlook them altogether, or accept Andersen or Pella as "the best windows on the market." The real truth is that the window companies with the largest marketing budgets have the lion's share of the residential window market - even though there are much better performing windows out there. Most contractors will stick with the manufacturer they are used to dealing with. I'd even venture to say that most don't fully understand the real performance difference between windows.

Let me pick on Andersen for a minute. Their "best" double hung, double pane, argon gas filled window, with grills, has a U value of 0.35. Our trusty calculator tells us the R value of these windows is just 2.86! How many of us want to fill our walls and attics with R=2.86 insulation?

Note: Window performance is measured in terms of U values. Insulation is measured in terms of R values. You can easily convert U values to R values and vice versa simply by entering the value in a calculator and pressing the "1/X" key.

This article could quickly become overly technical, but rather than do that, I prefer to keep this complex subject as simple as possible. Here are a few things to consider when choosing windows for your home:

• Brand name does NOT mean superior thermal performance
• Don't accept the builder's standard window without question (most will simply provide the cheapest windows that meet building code)
• Be sure to consider the long term "operating" cost of a window - how much heat is "going out the window"
• Use low-e coatings intelligently (low-e means lower passive solar heat gain)
• Remember, "cost" is relative, if you are on a budget just make sure the window costs are not excessive

I admit, I had a bit of sticker shock when I first saw the cost of our windows. However, after careful analysis, and much contemplation, they appear to be worth it.
It was pretty easy to figure out heat savings in a typical January. The low U value of the windows will help us save about 6,000 BTUs per hour (over the builder's grade windows, and that is all day, every day) in an average January - or ~4.4 million BTUs for the month (6,000 x 24 hours x 31 days). That means we are saving the equivalent of $110 in oil (at $25 per 1 million BTUs) just by having a better insulated window.

Heat gain is a little more complex to predict. We need to account for shading, sun angle, SHGC values of the windows, our position on the earth, and angle of incidence. While not simple, there is definitely a benefit to "orientation tuning" the windows.
It gets pretty cold during the winter months, here in New England, so our south facing windows are designed to let heat from the sun into the house (high SHGC values) and keep it in (low U values). In an average January we expect to receive passive solar heat gain of approximately 3 million BTUs. At current oil rates, the windows will provide about $90 per month in FREE, non-polluting passive solar heat.

(PS - If you use this strategy, don't forget to carefully plan to shade the south facing windows during the summer months or you'll be paying to remove that extra heat from the house with A/C.)

So...

• The oil cost equivalent of passive solar gain - $90
• The oil cost equivalent of heat savings - $110
• Total oil cost equivalent savings during an average January - $200

Then I compared the additional cost of these windows (over and above the cost of the "standard" windows) and their effect on our monthly mortgage payment. It seems that our added cost per year is roughly the same as our savings. However, the additional mortgage payment is tax advantaged; the heating payments are not, and never will be. Plus, how many people expect heating prices to go down over the next 30 years?
For those of you that would normally choose Andersen or Pella windows for the name, (I compared builders' grade (a.k.a. low cost) windows) the amount added to your mortgage would be less, and even easier to justify.

I also look at it like this...
The total cost of the windows and patio door in our house is less than the average cost of a new car. We get free heat from them. We keep more of the heat in the house. We will get a tax break on the mortgage payments. We will stay more comfortable. For every $1 in annual energy costs we save, we will add roughly $20 to the appraisal value of the house. We will reduce our carbon emissions. We will protect the environment for, and set the right example for, our children and for others to follow.

Alpen Energy Group, LLC produces some of the highest performing windows in the world.  In fact, they were selected as one of the top 10 green building products for 2007 producing windows with a center-of-glass rating of up to R20! Robert and Dave from Alpen were personally involved in helping us select the proper windows for this project.  I owe them much gratitude for their help and patience.