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Learning How to Choose the Best MN Replacement Windows – Part 2

As you may have gathered from Part 1 of this article, knowing what to look for when it comes to rating the windows that you get is important. This is because you need to know more about the ratings that they are given and the ones that you should choose when it comes to having your old windows replaced with new ones. The first ratings used are on part 1, but this list continues those ratings to watch out for.

Leaking of Air

AL (air leakage) is measured through cubic feet of the amount of air that is passed through a square foot of a window area. The loss of cool air and heat happens through the infiltration of the air through small cracks  in the window assembly. The lower this rating is, the less air will pass through this area.

Resistance to Condensation

This is shown as CR, and it is an indication of  the ability of the window to resist condensation on the inside surface. The higher this rating is, the better it is at resisting moisture build-up. It might not mean that condensation will never happen, but it gives you an idea of which windows might be better at resisting the condensation. It can be expressed from 0 to 100. This is also something that is optional, and it might not be included on the window label.

Performance Grade and Design Pressure

This is shown by DP and is tested using laboratory pressure of pounds per square foot. The requirements can vary depending on the specific windows. The positive numbers for DP are standard for the blowing of wind, and the negative number is the vacuum pressure that is put on the other side of the window. If the home is in a hurricane zone then these numbers are very important.  But here in Minnesota where we often get tornadoes and high winds, it can be a factor if your windows are in an exposed, open area.

Test Pressure Structurally

This is tested at 150% of the DP rating the window is given. This is tested in the glass, sash, and frame of the window and not just the glass. In order for the window to have a higher rating, testers look into the thickness and tempering of the glass and other components. Using higher-end hardware and sealants can also help with this rating.

Sounds Transmission Class

This is shown as STC and are used to average how sound is stopped when it travels through the window. This rating is used for doors, building materials, and walls on top of windows. The ratings will range from 18 to 50. If the window is double paned then the number will be from 28 to 35. The thicker the glass is, the less sound is going to travel through the window.

There are a number of factors to consider when comparing windows and evaluating what appear to be similar choices.  If you’ve got questions about choosing windows, we’d be happy to schedule a presentation at our showroom to allow you to inspect and evaluate the windows we offer.   We also provide free, no-obligation consultations, and our window experts can help make the task of interpreting all those numbers a little easier.



Window Outfitters is a premier Window Replacement, doors, siding contractor and installer. As Contractor in the St Paul, Minneapolis, (Twin Cities) Minnesota (MN) metro, we proudly serve, but are not limited to, the following areas: Minneapolis Energy Efficient Vinyl Windows, Replacement Window Contractors Minnesota, Burnsville, Apple Valley, Lakeville, Savage, Bloomington, Edina, Richfield, Eagan, St Paul, Hastings, Minnetonka, Plymouth, Maple Grove, Eden Prairie, Farmington MN, Chaska, Shakopee, Chanhassen, Victoria, Mendota Heights Anderson Windows Minneapolis, Marvin Windows Minneapolis.