I was replacing a window sill for a home owner the other day and she said she wished she had never replaced the old wooden windows with new replacement windows because the new ones are colder.
I thought that was a little strange and I have come to find out that is true with the windows in many homes and businesses purchased from some very well know manufacturers.
The energy performance of a window does not have anything to do with the name of the window manufacturer or the price you pay it has to do with the insulating factor known as the U-value.
This is where the deception begins when you read the U-Factor definition.
According to NFRC (National Fenestration Rating Council) - The U-Factor measures the rate of heat transfer and tells you how well the window insulates. U-factor values generally range from 0.25 to 1.25 and are measured in Btu/h·ft²·°F. The lower the U-factor, the better the window insulates.
What exactly does that mean to me someone interested in keeping my home warm?
If you take one and divide it by the U-Factor as shown in the figure (The NFRC label - found on new windows) you get the important R-Value. This is the energy insulating value when talking about the insulated walls in your home.
Why the U-factor they should be using a value that is already well known like the R-value.
Why is such a low insulating factor acceptable?
The walls in new homes in Massachusetts according to the new building codes must have a minimum R-19 value. Older homes have around an R-11.
You want the highest value R-Value because you will spend less on heating and cooling.
Now why do new windows have such a poor U-factor 0.35 which equals R-2.86, it is like having a hole in your wall. Go put your hand on the glass part of the window in the winter and you can feel the cold.
When you are looking for new windows:
- The lower the U-factor the better, for it to be close to an R-11 it should be 0.1 to be equal to an insulated wall in an older home.
- Do not just look at the purchase price think about what you will pay over the long term.
- You most likely will pay more for a lower U-factor window but you will be much more comfortable.
- If you find that the price for a new window is too high try covering the window with Plexiglas, it does a great job insulating for much less.