How To Measure a Window’s Energy Efficiency

You know energy efficiency is important when it comes to windows. But what does that mean, exactly? And how do you measure efficiency? At Zen Windows, energy efficiency features are standard on all our windows because we know it’s important for homeowners and the planet.

Because we use the most energy-efficient window materials, Zen Windows is a partner with the Environmental Protection Agency’s (EPA’s) government-backed ENERGY STAR® program. Zen Windows products are also approved by the Window & Door Dealer Alliance (WDDA) and recognized as EPA Lead-Safe certified.

Understanding the NFRC Label

Everything you need to know about a window’s energy efficiency is on the National Fenestration Rating Council label. NFRC criteria differs for each climate zone. Windows and skylights for your home’s location require different performance levels than in other areas of the United States.

The NFRC label will include:

  • AL: Air leakage measures how much air will enter a room through a square foot of window; lower is better.
  • CR: Condensation resistance is a window’s ability to resist interior condensation; higher is better.
  • SHGC: Solar heat gain coefficient measures the fraction of solar radiation admitted through a window on a scale of 0-1; lower is better.
  • U-factor: This measures heat loss on a scale of 0-1; lower is better.
  • VT: Visible transmittance indicates visible light. It’s measured using numbers between 0 and 3; higher indicates more light will be transmitted.

Performance Criteria for Energy-Efficient Windows

  • Frames: Vinyl and fiberglass are rated highest by
  • Gas fills: Argon or krypton gas fills provide greater insulation.
  • Low-E glass glazing/coatings: These filter damaging radiation and resist heat flow.
  • Panes: Double- and triple-pane windows are most efficient.
  • Spacers: Insulating spacers are best.

For a fast, free quote, call or contact Zen Windows.

Signs Your Windows Aren’t Energy-Efficient

It’s time to replace your home’s windows if they are:

  • Aging, deteriorating
  • Broken, damaged
  • Causing 10%–25% higher energy costs
  • Easily opened from outside
  • Leaking
  • Warped
  • Won’t shut/lock securely

Seeing is believing! Check out our window gallery to get an idea of what you need and want.

For a fast, free quote, call or contact Zen Windows.

Why Energy-Efficient Windows Matter

Window replacements can be fun. You can increase your curb appeal and become a neighborhood focal point. You can give your home a beautiful face-lift! Just don’t lose sight of what’s important when selecting replacement windows: energy efficiency.

Benefits of Energy-Efficient Zen Windows

  • Money savings: Everyone likes saving money. Energy-efficient windows will lower your monthly heating and cooling bills. The return on investment (ROI) can be as much as 65% or more. And even if you’re not planning to sell soon, the increase in property value is measurable.
  • More light: Radiation is transmitted by the sun, and the sun’s light can heat a room quickly. Thankfully, energy-efficient windows block harmful ultraviolet rays and radiant heat. Properly constructed windows will filter harmful rays so you can enjoy more natural light.
  • Reduced noise pollution: If the city sounds and the neighbor’s barking dog are not what you signed on for, your insulated, energy-efficient windows can enhance soundproofing.
  • Thermal comfort: Until recently, windows were simply openings for light and air. “Thermal” describes heat conductivity and transfer, so “thermal comfort” is how we feel: too hot, too cold, or just right. Today’s replacement windows regulate your thermal comfort by providing energy-efficient insulation against outdoor heat and cold.

Are you planning a home improvement project? Let’s partner for a fast, free, energy-efficient replacement windows quote. No hassles. We think the best time for your home improvement project is when you’re ready.

Call or contact Zen Windows.

The Best Window Materials

Zen Windows are made of the most energy-efficient materials: high-quality vinyl and fiberglass.


  • Costs more than vinyl
  • Is recyclable
  • Many varieties of wood-look patterns/colors
  • Requires minimal maintenance
  • Slightly more difficult to mold
  • Will not crack, fade, rot, rust, or warp


  • Costs less than fiberglass
  • Easily molded to fit any size/shape opening
  • Is recyclable
  • Least likely to crack, fade, rot, rust, or warp
  • Many varieties of wood-look patterns/colors
  • Requires minimal maintenance
[DisplayIfSet group=”Additional_Pages” setting=”warranties”]

All Zen Windows products carry a lifetime warranty. For most people, the deciding factor is affordability because both materials deliver the same quality.

[/DisplayIfSet] [DisplayIfSet group=”Additional_Pages” setting=”financing”]

We believe your home’s security is even more important than energy efficiency. Ask about financing options for safe, energy-efficient replacement windows.


Call or contact Zen Windows.

Local Ownership

Zen Windows is a national franchise, but every location is locally owned, so you get the advantages of industry-best practices and local knowledge. Our Zen Windows professionals care most about customer care – your customer experience – because they live in your community.

Your window project isn’t complete until you’re satisfied. Find your Zen Windows location today and call or contact Zen Windows for a fast, free quote.