Energy Efficiency

The energy-efficient properties in our windows and doors can reduce your energy bills and keep your home comfortable year-round. Learn how you can start saving immediately!

More Comfort. More Savings.
Go Energy-Efficient Today.
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What is Energy Efficiency?

Energy-efficient windows and doors have insulation that helps to keep heated and cooled air inside your home. Our windows feature low-E double or triple-pane glass and lightweight but strong vinyl frames, making them as energy-efficient as they are beautiful. This allows your HVAC system to work more efficiently, saving you money on your energy bills every month and lowering your carbon footprint. In addition, your home’s internal temperatures will be more consistent and comfortable year round.

If your energy bills are higher than they have been in the past and there’s not an obvious reason, your windows may be causing your HVAC system to work harder. Window World customers report saving money on their energy bills from the first month.

See How Much You Could Be Saving

Table of Contents

Discover Energy Efficiency

The Technology

Science Behind The Savings


1Low-E Glass

Low-E glass was created to minimize the amount of UV rays and unwanted temperatures into your home in all climates.

2Warm-Edge Spacer

Intercept’s™ warm-edge spacer insulates the exterior edges of a sealed unit and can tack on 5% savings on monthly energy costs.

3Vinyl Framing

Vinyl window frames are constructed with a complex array of compartments internally to help trap and repel unwanted weather.

1Advanced Weatherstripping

Airtight weatherstripping seals the sides, top and bottom frames of your door to prevent air infiltration.

2Insulated Core

Insulated polyurethane core provides an additional thermal barrier.

3Durable Frames

Composite frames resist rotting, rusting and warping to withstand constant exposure to the elements.

4Energy-Saving Door Lites

Decorative and ENERGY STAR-compliant door lites that allow light in but keep the elements out.

Climate Requirements

What It Means To Be ENERGY STAR® Certified

ENERGY STAR is a government-sanctioned symbol for energy efficiency, signaling credibility, sustainability and cost-savings to consumers. Browse below to explore what’s required to become ENERGY STAR-certified and how those requirements change based on climate.

Your Climate

U-Factor Requirements

U-Factor measures the rate at which heat flows through an object. The lower your U-value, the less heat your windows allow through them.

  • Northern: ≤ .27
  • North-Central: ≤ .30
  • South-Central: ≤ .30
  • Southern: ≤ .40

R-Value Requirements

R-Value determines how well the insulating layer inside your window is performing. The higher your R-value, the better insulated your window is.

  • Northern: 13 – 21
  • North-Central: 13 – 21
  • South-Central: 13 – 21
  • Southern: 13 – 21

In Colorado: You Need A High-Performing Insulated Product

Window World of Denver is located in ENERGY STAR’s Northern Climate category. To maintain certification in this area, windows and doors must register a U-Value of ≤ .27 and an R-Factor from 13 to 21.

Glossary Of Terms

Industry Terms You Need To Know

Low-E Glass

Low-E (low-emissivity) glass has been treated with a microscopic metallic coating designed to filter the amount of UV light that enters your home. By filtering the amount of UV light that enters your home, it keeps the heat gain lower in warm seasons and allows more heat in during cooler months. This keeps your home’s temperature more consistent year-round. By filtering out UV light, low-E glass also prevents fading on your furniture and window treatments.


U-factor measures the rate of heat transfer and how well a window insulates. It is measured on a scale from 0.20 to 1.20. The lower the u-factor, the more effective the window is at insulating.


R-value refers to a building material’s insulation level. Each region of the US has an energy-efficient r-value range for windows based on that area’s climate.

Argon Gas

Argon is an extremely dense colorless, odorless gas with very low thermal conductivity. It is used as insulation between double-pane and triple-pane windows. When paired with Low-E glass, it keeps the window closer to room temperature, helping eliminate drafts and increase energy efficiency.

Warm-Edge Spacer System

Spacers are placed between double and triple-panes of glass. In the past, they were mainly made of aluminum, which we no longer recommend due to its poor insulating properties. Our Intercept™ warm-edge spacer system extends the shelf-life of window glass by reducing condensation build-up and edge-to-glass temperatures. Designed to seal in escaping heat, this spacer system is the most effective on the market.

What Makes Windows Energy-Efficient?

Our Experts Explain Energy Efficiency

Our home improvement experts have all the answers to your energy efficiency questions on our blog. Check out our guide to energy-efficient windows and watch the video to the right to learn more!

Read More

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