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Best Regional Windows

How Windows are Rated for Performance in Different Climates 

Windows are measured by performance labels from the  National Fenestration Rating Council. The labels outline U-factor, SHGC, Visible Transmittance, and Air Leakage ratings—all of which can help you find the best windows for your climate. Let’s learn a little more about each performance factor.  

How to read an example NFRC Energy Performance label

Window U-factor  

U-factor measures how well a window keeps heat in your home. A higher number allows more heat to escape. U-factors range from 0.10-2.00.  

Window Solar Heat Gain Coefficient (SHGC) 

The SHGC measures how much heat from the sun enters a room. In a warmer climate, you’ll want a window with a lower SHGC number. Lower SHGC numbers reduce cooling costs and higher SHGC numbers can reduce heating costs. SHGC numbers range from 0.00-1.00. 

Window Visible Transmittance 

Visible transmittance (VT) measures how much natural light enters your home. It doesn’t account for heat entering your home, but VT can help homeowners modify their indoor lighting use by relying more on natural light. VT numbers range from 0.00-1.00. 

Window Air Leakage 

Air leakage ratings measure how much air will enter a room through a window. Air leakage rates of ≤ 0.3 mean fewer drafts.  

Window Glass Coatings 

Thin coatings of special low emissivity (Low E) metallic material get applied to glass panes to boost energy efficiency and block out UV rays. Low E has a number following the “E” to indicate the number of coatings.  

Marvin Replacement offers Low E1, Low E2, Low E3, and Low E3/ERS coatings. 

Our Low E3 and our Low E3/ERS glazing work well in warmer climates because they will block solar heat. A Low E3 window will block up to 95% of UV rays.  

Low E1 glass glazing works best in colder climates because it allows more heat in to warm a room while blocking heat loss. 

Low E2 works well in moderate climates because it can help retain heat in winter and reject heat in the summer. It blocks 84% of the sun’s UV rays to reduce color fading.  

Best Windows by Region 

Map of ENERGY STAR climate zones

Knowing the glass glazing options and ratings to follow can help you make an informed decision on the best windows for your region. Plus, Marvin Replacement’s Ultrex® fiberglass has a lower conductivity than other window materials, like aluminum, which means it can help keep heat and cold out of the home.

Marvin Replacement's Ultrex fiberglass windows, when paired with the ideal glass coating for your climate, may improve your home's energy efficiency.*

During your consultation, a Marvin Replacement design consultant will review your specific climate needs to find the right window and glass option for your home. 

Best Windows for Pacific Northwest 

Specific types of windows suit the Pacific Northwest better than others because of the cool, damp climate. Window materials like Marvin Replacement’s Ultrex fiberglass holds up well because it expands 87% less than vinyl and is 8x stronger than vinyl. Ultrex is designed to resist warping and weathering in any condition, which is important if you live in a rainy climate like Seattle or Portland, Oregon.  

The Pacific Northwest falls into the Northern region of the ENERGY STAR® Climate Zone Map and suggests windows with:  

A U-factor of 0.27 or less (any SHGC is allowed) or 

A U-factor of 0.28 and SHGC of 0.32 or more or 

A U-factor of 0.29 and SHGC of 0.37 or more or 

A U-factor of 0.30 and SHGC of 0.42 or more 

Windows with U-factors of 0.30 and less will retain more heat while windows with a higher SHGC number can help reduce heating costs.  

Best Windows for Southwest 

The Southwest experiences much more direct sunlight than other regions and needs windows that can help reject solar heat to keep cooling costs down.  

The Southwest encompasses all four ENERGY STAR® climate zones, so be sure to use the climate zone finder to get the best information about your climate zone.  

Windows with higher U-factors and lower SHGC numbers will typically work best in the Southwest. Glass with Low E3 or Low E3/ERS can block more solar heat and UV rays.  

Best Windows for Midwest 

The Northern region extends over much of the Midwest on the ENERGY STAR® Climate Zone Map, which means a need to harness more solar heat and a need to prevent heat loss to help reduce heating costs.  

Windows with lower U-factors and higher SHGC numbers help the best for homes in the region. U-factors of 0.30 or less and SHGCs of 0.32 or more work best.  

The low conductivity of Ultrex fiberglass helps homes retain more heat in winter and stay cooler in the summer, ideal for a Midwestern climate.

Best Windows for Northeast 

The Northeast falls into the Northern climate zone in the ENERGY STAR® Climate Zone Map where U-factors of 0.30 or less and SHGCs of 0.32 or more fit best.

Best Windows for Southeast 

The Southeast gets broken into the Southern and South-Central regions in the ENERGY STAR® Climate Zone Map, so consult the climate zone finder to find information specific to your county.  

Areas in the South-Central climate region, like Charlotte, North Carolina, should have windows with a U-factor of 0.30 or less and a SHGC number of 0.25 or less.  

Homes in the Southern climate region, like Austin, Dallas, and Houston, need windows with U-factors of 0.40 or less and SHGC numbers of 0.25 or less.  

Low E3 and Low E3/ERS glass glazing can help block UV rays and help keep homes cooler in the summer when they face more sunlight than other regions.  

Since Southern climates face higher temperatures and more direct sunlight, the low expansion rate of Marvin Replacement's Ultrex fiberglass windows paired with our energy efficient glass options is a great choice for Southern homeowners.

Schedule your free design consultation to learn more about the right energy efficient Marvin Replacement windows for your home.

* Savings reflect installing ENERGY STAR® certified products compared to non-certified when replacing single pane windows based on the average savings among homes in modeled cities. Actual savings will vary by product type, location, method of installation, individual home characteristics, local climate and conditions, utility rates, and other factors.


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