The very first thing to remember as you’re starting to sort through window ratings is that just about every aspect of a window’s performance can be relatively easily quantified. If you’re the kind of person who likes to get into the details of these things you’ll love shopping for windows. Just remember to keep an eye on the big picture. Don’t let yourself get all distracted by a 0.02 difference in one rating or another. Some companies will really try to get you focused on this rating or that in order to justify their price. Try not to lose sight of the forest for the trees as they say.
Remember that all features of a product only really matter if they affect the window ratings. For example, if a salesperson tells you that his windows are “better” because they have foam filled frames ask him what the u-factor is. If it’s better than another product you’re considering then it’s better. If the u-factor is not better that foam isn’t doing you any good. I guess an easier way to say this would be that you don’t care much about foam in frames or coatings on glass, windows filled with magic gas or anything else. You care about an efficient window. The method to get to the efficient product really isn’t all that important. The results are the important part and the results are easily quantified. There’s no need to take someones word for it.
So what are the basic window ratings to keep an eye on? They are:
- U-Factor vs R-Value
- solar heat gain coefficient or shgc
- visible transmittance or vt rating
- air infiltration or air leakage
- water penetration
- design pressure or dp rating
- sound transmission class or stc rating
- R5 volume purchase program
- condensation resistance or cr rating
We’ll also look at organizations related to window ratings including:
- NFRC ratings from the National Fenestration Rating Council
- AAMA Certification from the American Architectural Manufacturers Association
I’ll put together specific posts on each one of these window ratings explaining what they mean, what levels are considered good or great, where you’ll likely find the best bang for your buck and any tips or tricks for interpreting what they’ll actually mean to you.
If you’re not a physics teacher and not all that interested in delving into the minutia here, you may be looking for a way to tell if a specific product is “pretty good” without spending a tremendous amount of time learning all about the specific window ratings and that logic makes sense. To accomplish that goal, look for a product that meets the energy star requirements for your climate zone. Even though I’m writing this in February of 2014 there are already products available that meet the 2015 energy star guidelines and that would be something to consider. You can also learn about the structural performance of a product by looking at it’s AAMA rating. Gold is the best, then silver, etc. All major products are AAMA certified so if you come across one that isn’t or if a company won’t tell you the rating that would be a major red flag.
If a product meets the 2015 energy star criteria and it’s AAMA gold certified then you’ve got yourself a pretty solid window. If you want to get a deeper feel for how one product compares to another dig on into the window ratings. Keep an eye on future posts for LOTS of details!