If you’re looking to boost your home’s energy efficiency, you’ve likely encountered a variety of terms related to energy-saving windows. We’re here to clarify these concepts, including what it truly means for a window to be “Energy Star” certified.
But first, let’s define what makes a window energy-efficient.
What Defines Energy-Efficient Windows?
Energy-efficient windows are specifically engineered and constructed to prevent the escape of heated or cooled air from your living space.1 This design ensures your HVAC system operates optimally, avoiding unnecessary strain.2 The primary benefits include reduced electricity bills and more consistent indoor temperatures throughout the year.3
Decoding Energy-Efficient Window Terminology
Low-E Glass
Low-E (low-emissivity) glass is treated with a microscopically thin metallic coating.4 This coating is designed to regulate the amount of ultraviolet (UV) light entering your home.5 By filtering UV light, it minimizes heat gain during warmer seasons while allowing more heat in during cooler months, thereby helping to maintain a more stable indoor temperature year-round.6 An added advantage of Low-E glass is its ability to filter out UV light, which helps prevent fading of your furniture and window treatments.7
U-Factor
The U-factor quantifies the rate of heat transfer and gauges a window’s insulating effectiveness.8 It’s measured on a scale ranging from 0.20 to 1.20.9 A lower U-factor indicates superior insulation performance from the window.10
R-Value
R-value refers to the level of insulation provided by a building material.11 For windows, each region within the U.S. has a recommended energy-efficient R-value range, tailored to its specific climate.12
Argon Gas
Argon is an exceptionally dense, colorless, and odorless gas with very low thermal conductivity.13 It’s used as an insulating fill between the panes of double-pane and triple-pane windows.14 When combined with Low-E glass, argon helps maintain the window’s temperature closer to the room’s ambient temperature, which effectively eliminates drafts and boosts overall energy efficiency.
Warm Edge Spacer System
Spacers are positioned between multiple panes of glass in double and triple-glazed units.15 Historically, these were often made from aluminum, a material we no longer recommend due to its poor insulating properties.16 Our Intercept™ warm-edge spacer system significantly extends the lifespan of window glass by minimizing condensation buildup and improving edge-to-glass temperatures.17 Engineered to trap escaping heat, this spacer system is recognized as one of the most effective options currently on the market.
Understanding Energy Star Window Requirements
All Window World windows proudly carry the Energy Star certification, an endorsement granted to energy-efficient windows, doors, and skylights.18 To attain this certification, products must fulfill specific criteria:
- They must be manufactured by an ENERGY STAR partner.19
- They must undergo independent testing, certification, and verification by the National Fenestration Rating Council (NFRC).20
- Their NFRC ratings must comply with rigorous energy efficiency guidelines established by the U.S. Environmental Protection Agency (EPA).21
To meet the required NFRC ratings, these products must satisfy particular performance standards based on their designated climate zone.22 The U-factor and Solar Heat Gain Coefficient (SHGC) requirements for windows to be considered Energy Star in each climate are as follows:
- Northern:
- North-Central: 23
- South-Central: 24
- Southern:
How to Assess Your Windows for Energy Efficiency
To determine if your current windows are energy efficient, you can utilize a U-Value kit.25 This widely used tool measures heat loss around various types of windows in your home. Because they can take measurements during both hotter and colder months, U-Value kits are suitable for year-round use.26 The data gathered from these measurements will help you pinpoint areas where energy is escaping, enabling you to formulate a plan to address these issues.
Identifying the Most Energy-Efficient Window Option
Firstly, it’s important to understand that a window’s shape does not influence its energy efficiency. The key determinants are the frame material and the glass type.
At Window World, we exclusively offer and install vinyl windows because they combine energy efficiency, longevity, and affordability.27 We advise against aluminum windows, as aluminum is a poor insulator and its frames are prone to damage during storms. While wood windows are energy efficient, they generally have a shorter lifespan than vinyl and tend to be considerably more expensive.
Regarding the glass, your best choice is either double-pane or triple-pane glass. Single-pane glass is highly inefficient and not recommended.28 Incorporating argon gas between panes offers excellent insulation, particularly beneficial for those living in extremely hot or cold climates.29 Always opt for Low-E glass and thoroughly check the Energy Star level to ensure it meets the U-factor requirements for your specific region.
In summary, a double or triple-pane vinyl window with Low-E glass represents the most energy-efficient window option available.
Enhance Your Home’s Energy Efficiency with Window World
Every window we construct and install is built with a focus on quality and energy efficiency. However, our dedication to helping you save money through energy-efficient home products doesn’t end there. We’re also proud to provide energy-efficient doors. To learn more and discover how we can transform your home, explore our window selection and schedule your free consultation today.