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A Marvin Replacement window installers uses a caulk gun to seal a window.

How to Find the Best Energy Efficient Windows

Your windows and patio doors can help make your home more energy efficient. Here’s what to know when looking for energy efficient windows.

Energy Efficient Replacement Windows

The best energy efficient replacement windows have two or more glass panes. They also have an insulating gas fill and low emissivity coatings (Low-E)

Low E

E stands for emissivity, which is a material’s ability to radiate energy. The number following the “E” indicate the number of metallic layers. Marvin Replacement windows and doors have four choices of Low E coatings. The coatings are thin metallic layers designed to reflect heat. Marvin Replacement Low E options are: Low E1, Low E2, Low E3, and Low E3/ERS. 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. 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.

. Energy efficient windows get made with material that reduces heat transfer, too.

Most windows manufactured today feature two panes of glass. In the past homes used single-pane windows

Single Glazing

One layer of glass or other glazing material.

. Double-paned windows are more energy efficient than single-pane windows. Double-pane windows also feature a gas fill between the panes for energy efficiency. A non-toxic, inert gas, like argon is typically used for a gas fill. Argon has a greater density than air and reduces heat transfer.

Windows with Low-E glass coatings have thin metallic coatings to reflect heat. Different coatings work well in different climates. The best windows for hot weather have coatings that block solar heat. The best windows for cold weather allow more heat to enter a room. Marvin Replacement has four low-E coating options (Low E1, Low E2, Low E3, and Low E3/ERS). One of the options can meet the needs of your climate zone.

Different window materials have better energy efficiency than others. Marvin Replacement’s Ultrex® fiberglass insulates better than aluminum. Ultrex helps reduce heat transfer.

What are the Most Energy Efficient Windows?

An easy way to find the most energy efficient windows is to look for windows with the ENERGY STAR® logo. ENERGY STAR-certified windows have met ENERGY STAR standards for energy efficiency.

Example of a National Fenestration Rating Council window performance label.

A National Fenestration Rating Council (NFRC) window label explains the energy efficiency of a window. A NFRC label helps you compare energy-efficient products. It displays things like:

  • U-factor


    U-Factor is a measure of how well a window retains heat in a home. A higher U-Factor allows more heat to escape a home and a lower number will allow less heat to transfer out of a home.


  • Solar Heat Gain Coefficient (SHGC)

    Solar Heat Gain Coefficient (SHGC)

    Solar Heat Gain Coefficient measures how much heat from the sun enters a home. A lower SHGC number allows less heat.


  • Visible Transmittance (VT)

    Visible Light Transmittance (VT)

    Visible transmittance is the measure of visible light that will pass through a window. A higher VT number maximizes daylight.


  • Air Leakage

    Air Leakage

    Unintended air that passes through a window.


U-factors range from 0.10 to 2.00. Higher U-factor numbers allow more heat to escape. SHGC numbers range from 0.00 to 1.00. Those in warmer climates will want windows with a lower SHGC number. Air leakage rates of ≤ 0.3 mean fewer drafts. ENERGY STAR has a climate zone finder tool with U-factor and SHGC number suggestions.

Energy Efficient Windows Benefits 

  • Save Money: Replacing energy inefficient windows with new energy efficient windows can save you money.* Energy efficient windows help your home keep heat in cooler months. They also prevent heat from entering during warmer months.

  • Protect from UV Rays: The type of window glass you choose can help protect items in your home from color fade. Low-E glass helps block UV rays, which can damage furniture color.

  • Feel Comfortable: One of the signs to replace windows is when you start to notice drafts. Upgrading to energy efficient windows is one of the best ways to reduce energy loss with windows.  

How Much Can You Save with Energy Efficient Windows? 

The NFRC estimates the average American household spends $1,500-$2,500 annually on energy bills. About 45% of that goes toward heating and cooling costs. 

The U.S. Department of Energy (DOE) estimates a homeowner can save between $101 and $583 a year on average, if they’re replacing single pane windows with ENERGY STAR-certified windows. For double pane windows, those savings range between $27 and $197.*  

Tax Credit for Energy Efficient Windows 

Tax credits for energy efficient windows vary between legislative sessions. Energystar.gov has the most up-to-date information on energy efficient tax credits.  


Which is more energy-efficient single-hung or double-hung windows?

The difference between single hung windows vs. double hung windows is only one sash


The operating and/or stationary portion of the window that holds the glass and is separate from the frame.

moves in a single hung window. That means fewer paths for air leakage. Both types of windows seal tightly and are energy efficient.   

Why is energy efficiency important? 

Energy efficiency means using less energy to perform the same function. An easy example is energy efficient lightbulbs. An energy efficient lightbulb will still light a room but use less energy to do so. Energy efficiency is not the same as energy conservation. Energy conservation means reducing a good or service to save energy. Using the lightbulb example, turning off a light is energy conservation. 

*Savings reflects 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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