What The Commercials Don’t Tell You About Replacement Windows

Here in the Detroit area replacement window manufacturers bombard us constantly with enticing deals claiming to save money on our energy bills. We see it on TV, in print and online. "Save up to 50% on your heating and cooling costs by installing our top of the line windows." Wow! Where do I sign up?

But let’s take a step back. Perhaps it is too good to be true. Based on the research I’ve been doing lately in the realm of energy audits, today's top of the line thermal insulated double glazed replacement windows are not much better that yesterday's single pane window with storm windows at keeping the heat in and out. Some of the glass coatings have helped a little, but little is the operative word there. Glass technology has actually not changed much in 2,000 years.

So where do we go from here? First, here’s a short primer on "R-values." The ability of a given material to resist heat transfer from the hot side to the cold side is measured in R-values. The greater the R-value the better insulating qualities that material has. Here in Southeast Michigan, new construction codes say the attic must be insulated to a minimum R-38 (about 12 inches of fiberglass). The walls must be insulated to a minimum R-13 (about 3.5 inches of fiberglass). And the state powers would like to increase those minimums to R-49 and R-19 respectively. Impressive numbers.

Now let's look at window R-values. Replacement windows are rated using their "U-values". Simply put, R-values and U-values are inverse to each other. Replacement window manufacturers say "why use U-values for windows and R-values for about everything else?” Walls are built to stop the outside from coming in while windows are added to allow the outside to come in. Walls stop heat and light - windows pass heat and light. Really simplified - when a person builds a wall they want to know how much of the outside is going to stay outside - and when a person installs a window, they want to know how much of the outside the window is going to allow inside. Walls resist heat flow and R-value measures resistance to heat flow; U-value measures heat flow and windows pass heat."

Energy Star qualified windows must have a U-value of 0.35 or less in the Northern Climate (mostly heating) environment. A U-value of 0.35 is an R-vale of 1/0.35 = 2.9. 2.9!! Put into plain English, those windows are like big holes in the walls. And today's replacements do not do much to improve these holes.

But there is progress. There are triple paned windows. Some glass manufacturers are developing R-11 glass. Coating manufacturers are improving their products, too. There is one window company called Serious Windows that advertises high efficient vinyl replacement windows. It appears to be a good product but I don't know anyone who could afford them.

So now for the bottom line: replace your windows? Yes, but for the convenience; maybe you no longer want separate storms and screens. Yes, because they are rotted, inoperable or have failed seals. Yes, because you have single pane windows. These are all good reasons for window replacement. But replace your windows to save up to 50% on your heating and cooling bills? From where I’m sitting, that’s a siren song of disappointment.

Does anyone disagree? Let me know what you think in the comments below.