Nashville's Definitive Guide To Window Energy Efficiency

Are you a Nashville homeowner scouring the internet 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.

We’ve created the 2018 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 will 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.

Skip To A Section:

Section I:

How Much Do Energy Efficient Windows
Save Nashville Homeowners?

(And How Much Do They Cost?)


Energy Star is the country’s authority on window energy efficiency. They have concluded that Nashville residents can save up to $349 per year on energy bills when they replace their old single pane windows with Energy Star-certified windows.


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 you can get vinyl replacement windows for around $450 to $600 (including installation!).

Section II:

How To Read A Window’s NFRC Label

You can determine almost everything about a window’s energy efficiency from its NFRC 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 the rate of heat loss between a numerical value of 0 and 1. The lower the U-Factor number, the better the window keeps heat within the home. Well-insulated windows with a low U-Factor keep your home a comfortable temperature year round and while reduce 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 numerical value 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 visible light passes through a window. VT includes the impact of the frame that doesn’t transmit any visible 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. 0.1 is considered outstanding; 0.2 is good; 0.3 is average; 0.4 or higher is poor.

Note: You will notice that an exact value of Air Leakage is not printed. Lobbying by the majority of 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. Please ask any salesman you let into your home what this number is and verify it! Our windows (which are manufactured by Soft-Lite) 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 air infiltration rates of our windows for more details.


Condensation Resistance

Condensation Resistance measures a window’s ability to resist the formation of condensation on its interior surfaces. 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.

Section III:

Anatomy Of An Energy Efficient Window

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


If you want to cut energy costs and help keep your home a comfortable temperature 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 in between each pane. Not only will you experience better efficiency, but your windows will also be able to 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 amount of VISIBLE light that gets through. This allows plenty of sunshine into your home while also protecting your indoor furnishings from fading. Low-e coating also reflects heat from both inside and outside your home, which helps maintain a cooler home in the summer and a warmer home in the winter.

Diagram showing different energy efficient window components.


As mentioned above, gas in between the glass panes provides your windows a huge efficiency boost. The gas itself is usually krypton or argon, which are denser than air to provide 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 contain high-density insulation on the inside. These features offer the best protection against air leakage and heat loss, and are typically found in high-quality vinyl windows.


Spacers are the seals in 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 your best bet for maximum insulation around the edges of a pane.


Even the most energy efficient window will fail if it is improperly installed. The poorer the window’s installation, the poorer the energy efficiency. On the other hand, if a contractor installs yours windows straight, tight, and exactly to manufacturer instructions, you can expect maximum efficiency. Make sure you perform your due diligence on a contractor (i.e., look at reviews, references, certifications, etc.) before hiring them to ensure you get quality installation.

Section IV:

Why We Have THE Most
Energy Efficient Windows In Nashville

At Zen Windows Nashville, our philosophy is simple: Install THE absolute most energy efficient windows on the market. To achieve this lofty goal, we’ve partnered with Soft-Lite, one of the industry’s most established and respected window manufacturers, to bring you multiple exclusive lines of award-winning energy efficient vinyl replacement windows

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

  • Energy Star has awarded 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 a comfortable temperature 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.

Get A 5-Minute Quote

Visit our Get A Quote page for a quick and accurate estimate on our energy efficient windows for Nashville. If you have questions, you can also contact us. We’d be happy to provide you with more information.