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Thermal Ratings: Climate and Performance

Shopping for replacement windows entails more than simply looking for a style one is fond of. Different types of windows perform better in certain climates than others. If you live in a particular area or climate of the United States; you may find you have different results than someone on the other side of the country. No two shoppers are going to have the same needs out of their windows. It is imperative for a consumer to understand the features they want and need.

The follow section will offer some rule of thumb guidelines for selecting windows based on one's area in the contiguous United States. Alaska and Hawaii stand fairly alone in their climates when compared to the body of the United States. Thermal performance will be fairly consistent for both of them in their respective locations.

The Northwestern Region

The North-West United States is a region often associated with rainfall due to the presence of the Pacific Ocean. The further one goes from the coast, one can expect there to be drier climates. The general climate of the area is cool and damp a majority of the year. If one lives at a higher altitude, they can expect heavier snowfalls and bitterly cold weather.

Lower Altitude

U-Value: A mid to lower U-Value will provide sturdy insulation in summer or winter.

SHGC: Leaning towards a mid to higher SHGC rating will allow more natural heat.

AL: A low air leakage will be more favorable for colder weather.

CR: Condensation Resistance is an important value in the North-Western Region. One should definitely seek a high CR to help ward against internal water damage.

Higher Altitude

U-Value: The U-Value at higher altitudes should be towards the lower end.

SHGC: A high SHGC will help ease the impact of heating bills.

AL: A low air leakage rating will go further to maintaining a comfortable home.

CR: Condensation Resistance will likely not be as important at higher altitudes. A mid-range to high CR will provide the protection needed.

The High Plains Region

The High Plains Region of the United States includes states such as North and South Dakota, Minnesota, Kansas, and Nebraska. Winters tend to be bitterly cold with snowfall while summers tend to be mildly warm with lighter precipitation. The further south one gets in the region, the less extreme it tends to be.


U-Value: The bitter cold nature of the area will make a high U-Value necessary.

SHGC: A mid to high SHGC will be favorable during winter months.

AL: The AL rating of the window should be as low as feasible to prevent air transfer.

CR: A mid-range or higher CR would be a good idea with the difference in temperature from outside to inside during winter months.

The Midwest (Ohio Valley) Region

This area is prone to differences in weather thanks to Lake Effect from the Great Lakes. Winters are typically cold but not bitterly so. Summers can get hot but are generally milder due to the presence of the lakes. The further north one gets in the region, the deeper the temperature dips. The southern reaches of the region tend to get more precipitation thanks to the Gulf of Mexico streams that cross it.


U-Value: A product with a higher U-Value will provide good insulation in either season.

SHGC: The solar heat gain is not going to play a major role in balancing utility bills in this region. Higher helps, but is not necessary.

AL: The AL should be fairly low since the summer and winter months both get to far enough extremes to be uncomfortable. Keeping steady interior temperatures will rely on this factor.

CR: Due to the close proximity to the Great Lakes and the overall dampness of the area, a higher CR will be a sound value.

The Mid-Atlantic (New England) Region

The north-eastern United States is home to some specific climate patterns of its own. Commonly referred to as the Nor'easter; it is a storm system that develops near the Gulf of Mexico and slowly traverses the coast up towards Maine. This system generally dumps a tremendous amount of precipitation on the area in the form of snow or rain depending on the season. The further north one is, the colder the region generally is. The southern portion of the region tends to not be as bitterly cold.


U-Value: Insulating properties of a window will play a heavy role in the winter months. One should lean towards a higher U-Value.

SHGC: A higher SHGC will help in this region but will not play a major role in heating or cooling efficiency.

AL: Air Leakage should be a heavily considered factor especially going into the winter months. This value should be as low as possible to help prevent too much cold air from leaking in.

CR: This is another region that experiences a lot of precipitation and humid weather. A high CR will help to keep condensation down on the interior of the window.

The Southeast Region

The South-East United States is generally cool and mild during winters. They do not experience temperatures low enough to get snow except on a freak occurrence. The Nor'Easter weather pattern can drop an extreme amount of rain on the area as it moves up along the coast. Temperatures in the summer tend to be hot, humid, with many thunderstorms and rainfall to compliment it.

U-Value: Insulating properties of the window will mainly matter in the hot months. If one expects to use air conditioning a high U-Value should be sought.

SHGC: One will want to tend towards a middle to low range SHGC for this region. The hot, humid nature and closer proximity to the Equator equates into more direct sun than other regions.

AL: Air Leakage will be a major consideration during hot months with air conditioning going. A lower AL will be preferable for this region.

CR: The extremely wet and humid nature of the region will make condensation a problem. Look for a high CR product to help keep moisture in control.

The Southern Region

The Southern United States is comprised of Arkansas, Texas, Oklahoma, Louisiana, and Mississippi. Winters in the south are generally cool days with colder nights. Summers are extremely humid and hot. The great difference is due largely to the desert climate that makes up a majority of the area. The further north one goes, one may expect to find snowfall in winter months.


U-Value: A higher U-Value of windows will be valuable in this region thanks to the hotter temperatures in summer.

SHGC: A mid to low range SHGC is preferable because of the location of the region. In such a hot area, one wants to deflect off more of the natural sun energy.

AL: A low AL will help keep air transfer to a minimum during extreme temperatures. Though it won't be as much of a problem in the winter; the summers can be uncomfortable.

CR: This area is generally very humid with a lot of thunderstorms thanks to the Gulf of Mexico. The further north one goes the less precipitation can be expected. A moderate to high CR rating will help keep interiors drying during summer months.

The Southwestern Region

This area of the United States tends to be fairly dry and cool during winters. During summer months, dry and warm. Periodically, weather systems do come off of the Pacific Ocean but it is not a very common occurrence. Higher altitudes in the mountains do cause greater amounts of snowfall and colder temperatures (suggested values for this can be found under Higher Altitude in the North-Western section).


U-Value: U-Value is not of great importance in this region as it is in others. Insulating qualities would be comfortable in a U-Value mid-range.

SHGC: This section of the country is often warm and sunny for much of the year. A moderate to decent SHGC can help to maintain a comfortable living area.

AL: Air Leakage is not as great of a consideration in this area due to the relative mildness of the climate. Mid-range would be the highest SHGC one should feel comfortable with.

CR: Condensation is going to be almost non-existent in this region. The rating will be negligible.

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