Energy Efficiency Replacement Windows

A Guide to Energy Efficient Windows

5 min read

If you’re looking to increase your home’s energy efficiency, you have probably realized there are a lot of different terms involved with energy-saving windows. From demystifying these terms to explaining what it means to be “Energy Star” certified, we’ll explain everything here.

But first, what does it really mean if a window is energy-efficient?

What Are Energy-Efficient Windows?

Energy-efficient windows are designed and built to prevent heated or cooled air from escaping your home. This ensures your HVAC system doesn’t work harder than it needs to. The benefits are lower electric bills and more consistent temperatures in your home year-round.


Energy-Efficient Window Terms Explained

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.

Energy Star Window Requirements

energy star logoAll Window World windows have earned the Energy Star certification that is given to energy-efficient windows, doors, and skylights. To earn this certification, these products must be:

  • Manufactured by an ENERGY STAR partner
  • Independently tested, certified, and verified by the National Fenestration Rating Council (NFRC)
  • Have NFRC ratings that meet strict energy efficiency guidelines set by the US Environmental Protection Agency (EPA)

To earn the required NFRC ratings, these products must meet certain performance standards based on the climate zone. The u-factor and solar heat gain coefficient (SHGC) requirements for windows in each climate to be considered Energy Star are below:

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

How Do You Know If You Have Energy-Efficient Windows?

To determine whether your windows are energy efficient, you can use a U-Value kit. The U-Value kit is a commonly used tool to measure heat loss around different types of windows in your home. Because they are able to measure during hotter and colder months, U-Value kits can be used year-round. With these measurements, you can determine where energy is leaking from and make an action plan to fix the problems.

What is the Most Energy-Efficient Window?

First, it’s important to know that the shape of the window doesn’t have an impact on energy efficiency. The frame material and glass are what determines the window’s energy efficiency.

At Window World, we offer and install vinyl windows because they are energy-efficient, long-lasting, and affordable. Aluminum windows are not recommended because aluminum is a poor insulator and the frames tend to sustain damage during storms. Wood windows are energy efficient, but they have a shorter lifespan than vinyl and tend to be much more expensive.

When it comes to the glass, you’ll want to choose double or triple-pane glass. Single pane is not recommended because it is very inefficient. Argon gas is a great insulator, especially for those in especially hot or cold climates. Opt for Low-E glass and double-check the Energy Star level to ensure it meets the u-factor requirements for your region.

In summary, a double or triple-pane vinyl window with Low-E glass is the most energy-efficient window option.

Make Your Home More Energy-Efficient With Window World

Each window we build and install is built with quality and energy efficiency in mind. But our commitment to saving you money with energy-efficient home products doesn’t stop there. We’re also proud to offer energy-efficient doors. To learn more and discover how we can transform your home, explore our window selection and schedule your free consultation today.

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