Do I really need to replace all my windows?

Paying attention to efficiency ratings can help in making this big decision

We recently purchased a little cabin up north. Last fall, as I walked past two windows, I felt a cold breeze blowing through them. They were about 30 years old and had once been functional double-pane windows. I used one and a half rolls of paper towels to temporarily fill the gaps. They had to be replaced this summer and it was time to do some research. This is what I found out.

Most of us are familiar with the term “R-value.” Jeremy Cook is an engineer who writes for Home Depot. He defines R-value as “a measurement, a rating, which corresponds to heat transfer through conduction. The higher the rating, the better the material resists heat transfer,” he says. In New Mexico, wall insulation should have an R-value of 19-21. But what about windows?

Windows are the weakest link in the energy efficiency of a building. They leak heat in winter and add heat in summer. The standard today is a Low E double-glazed window with argon gas between the panes. But even the best of them won’t give you much more than an R-3 value.

Energy Star, the government rating system, has computed the average annual cost savings of replacing single-pane and double widows. Replacing my leaky cabin windows might save me at least a couple of hundred dollars in heating bills a year.

Windows are no longer rated by R-value. What you will find is an Energy Star label that will tell you if the window is energy efficient. But look for an NFRC (National Fenestration Ratings Council) certified product. This rating system gives you much more information. It includes the “U-factor,” which measures how well the window will keep heat from escaping from inside a room. The lower the number the better. The range is from .201.20. Another rating measures the Solar Heat Gain Coefficient. In this climate, we don’t want heat entering a window in the summer. This rating measures how a window resists unwanted heat gain in the hot time of the year. The range is 0-1. The lower the number, the less you will spend on air conditioning. There is a rating for air leakage and for light transmittance. You can also get an NFRC condensation rating.

But you can significantly cut that winter heat loss or summer heat gain with window coverings. Triple-cell shades can increase your window R value by up to 5. Insulated drapes will also help.

Some people think that to save money on heating bills and cut their carbon footprint, they should upgrade all their windows. That may be aspirational, but it is not always cost-effective. Windows are not walls. You will always lose some heat, even with the best, most expensive windows.

So when should you replace your windows and what should you spend? If your windows are not too old, they are probably Low-E double-pane with argon gas between the panes. But that gas will leak out over time. When we bought our house, it was 8 years old. There were a couple of windows that looked cloudy. This is a sign of leaking argon gas. We asked the seller to replace them by Closing. The seller hired a local glass company. We were given a warranty. A year or two later, they were cloudy again. They had not been properly sealed. We called the company who installed them. “Oh”, they said, “that warranty we gave you only covered the cost of the windows, you will still have to pay us for our labor.” Their initial shoddy labor was the reason the new windows failed! Be careful.

Make sure you work with a qualified window installer.

Argon gas is colorless, nonflammable, odorless and nontoxic. It is denser than air and has a 34% lower conductivity, so improves the thermal insulation efficiency of windows. If you think you have lost some of your argon, look for cracks along the border of your window. Are they cloudy? Do the windows condensate? Check your warranty. It may be better than the one we were given. Also, installers now are able to inject argon into the gap in the panes and reseal them with some success, but that may only be a temporary solution. You may have no choice but to upgrade. When you do, you will find a range of prices. Don’t worry about R-value. Look for the NFCR rating. You want a low “U” rating and get the most energyefficient ones you can afford.

Judith Polich, a longtime New Mexico resident, is a retired attorney with a background in environmental studies and is a student of climate change. She can be reached at judith.polich@gmail.com