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Window Energy Efficiency

Nashville’s Definitive Guide to Energy Efficiency Windows

Are you a Nashville homeowner searching for the most energy-efficient replacement windows? Are you banging your head against the wall trying to make heads or tails of terms like “U-Factor” and “Solar Heat Gain Coefficient”? Do you want DEFINITIVE answers on what makes a window energy-efficient?

Then you’ve come to the right place.

There’s a lot to know about energy efficiency, especially for replacement windows. Zen Windows Nashville doors and windows offer the greatest energy efficiency possible. We have levels of energy-efficient performance based on your glass and frame choices, but even our lowest-rated replacement window is more energy-efficient than most.

We’ve created the 2022 Guide to Energy-Efficient Windows in Nashville to answer all your questions and help you make the BEST buying decision for your home.

By diving into the guide below, you’ll learn about the components of an energy-efficient window, how much efficient windows can reduce your utility bills, how to read a window’s NFRC label, and more.

How Much Do Energy-Efficient Windows Save Nashville Homeowners?

(And How Much Do They Cost?)

Savings: ENERGY STAR® is the country’s authority on window energy efficiency. They’ve concluded that Nashville residents can save up to $465 per year on energy bills when they replace their old single-pane windows with ENERGY STAR-certified windows.

Price: To get the most energy-efficient windows, you don’t have to spend a fortune. Vinyl is the premier material for window energy efficiency, and it’s more affordable than wood (it requires less maintenance, too!).

How To Read a Window's NFRC Label

You can determine almost everything about a window’s energy efficiency from its NFRC (National Fenestration Rating Council) label. The NFRC label is attached to all ENERGY STAR-certified windows and details a window’s energy ratings in five to six key categories.

Keep reading for a breakdown of each energy category.


U-factor measures how well your window keeps indoor heat from escaping. The factor can range between 0 and 1.20. The lower the U-factor number, the better the window keeps heat in the home. Well-insulated windows with a low U-factor keep your home a comfortable temperature year-round while reducing utility bills.

Solar Heat Gain Coefficient

Solar Heat Gain Coefficient (SHGC) measures the fraction of solar radiation allowed through a window. SHGC is expressed as a number between 0 and 1. Lower numbers are more desirable, except in northern climates where solar warming is beneficial in cold months. 

Visible Transmittance

Visible Transmittance (VT) calculates how much light passes through a window. VT includes the impact of the frame that doesn’t transmit any light. VT is expressed as a numerical value between 0 and 1. Higher numbers mean more daylight gets through.

Air Leakage

Air Leakage (AL) measures how much air enters a room through a square foot of window. The lower the number, the fewer drafts you’ll experience. ENERGY STAR air leakage rating as of 2016 is ≤0.3 cfm/square foot. 0.1 is considered outstanding; 0.2 is good; 0.3 is average; 0.4 or higher is poor.

Note: You will notice an exact air leakage value is not printed. Lobbying by most window manufacturers allowed this; 0.3 (thirty-hundredths CFM) is the minimum value required for an ENERGY STAR rating and is the standard most companies build to. Ask any salesperson who visits your home what this number is and verify it! Our windows have air leakage numbers ranging from 0.01–0.07 (one-hundredth to seven-hundredths CFM). Note that these numbers are hundredth decimals — not tenths! — making our windows almost five times more airtight than industry standards. Read this report about our windows’ air infiltration rates for more details.

Condensation Resistance

Condensation Resistance measures a window’s ability to resist the formation of condensation between panes and inside the frame. Measurements are expressed between 1 and 100, with higher numbers being better. Anything under 50 is poor; 50 to 60 is good; 60 or more is great.

Anatomy of an Energy-Efficient Window

For a window to be energy-efficient, it must have several high-quality components working together. We examine these components below.


If you want to cut energy costs and help keep your home comfortable year-round, two or three glass panes in your windows are necessary. Multiple glass panes offer more insulation because they allow high-density gas or air between each pane. Not only will you experience better efficiency, but your windows will also better resist impacts and outside noises.


Low-E is a coating applied to the glass of a window. It reflects ultraviolet and infrared light without diminishing the visible light that gets through. This allows plenty of sunshine into your home while protecting your indoor furnishings from fading. Low-E coating reflects heat from inside and outside your home, which helps maintain a cooler home in summer and a warmer home in winter.

Diagram showing different energy-efficient window components.

As mentioned above, gas between the glass panes gives your windows a huge efficiency boost. The gas is usually krypton or argon, which are denser than air for better insulation. These gases are odorless, colorless, non-toxic, and completely safe.


A superior frame is important to a window’s energy efficiency. The most energy-efficient window frames are fusion-welded at the corners and have high-density insulation inside. These features offer the best protection against air leakage and heat loss and are typically found in high-quality vinyl windows. For energy efficiency and value, vinyl frames are best. They are lower maintenance and thermally superior to aluminum, metal, or wood frames.


Spacers are the seals between the glass panes and play an important role in determining the amount of heat and cold that passes through a glass pane. Non-metallic and metal/non-metal hybrid spacers are best for maximum insulation around the edges of a pane.


The poorer the window’s installation, the poorer the energy efficiency. You can expect maximum efficiency if a contractor installs your windows straight, tight, and precisely to manufacturer instructions. Make sure you do your due diligence on a contractor (i.e., look at reviews, references, certifications, etc.) before hiring them to ensure a quality installation. At Zen Windows, we take pride in our skills, experience, and company. We want the best possible quality of work for our friends and neighbors (like you).

Why We Have the Most Energy-Efficient Windows in Nashville

At Zen Windows Nashville, our philosophy is simple: Install the most energy-efficient windows on the market. To achieve this lofty goal, we partner with established and respected window manufacturers to bring you multiple exclusive lines of award-winning, energy-efficient vinyl replacement windows.

Here’s why our windows are the best choice for Nashville homeowners looking for the utmost energy efficiency:

  • ENERGY STAR has named our windows “Most Efficient” on the market for the past three years.
  • From low-E coatings to fusion-welded frames to double- and triple-pane options, our windows come with every energy-efficiency feature you need to keep your home comfortable and your energy bills low.
  • Even our lowest-priced window line includes the most cutting-edge, energy-efficient features in the industry. You get fantastic energy efficiency, no matter which Zen Windows line you choose.

Fast and Accurate Quote

Thanks to technology, we don’t require a home visit to get a quoteYou pay no money until your project is finished. And don’t let money keep you from getting the energy-efficient windows you need. Ask about flexible financing options.

The best services, the best warranty, and the best windows and doors are yours with Zen Windows. Call 615-424-8102 or contact Zen Windows Nashville to learn more.

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