MR Premium Windows

U-Factor, SHGC and Low-E: A Georgia Replacement Window Guide

Compare replacement window ratings with confidence

Two replacement windows can look similar and have different energy ratings. For homeowners in Georgia, the useful question is how each option fits the room, its sunlight, and the local climate.

Start with three terms: U-factor describes insulation, solar heat gain coefficient (SHGC) describes incoming solar heat, and Low-E describes a coating on the glass. Reading them together helps you ask more specific questions before choosing a window.

Read the NFRC label first

The National Fenestration Rating Council (NFRC) provides independently certified energy-performance ratings. Its whole-product approach lets you compare the window assembly rather than relying on a claim about the glass alone. Ask for the label or certified ratings for the exact window configuration in your proposal.

The NFRC consumer guide to window ratings explains the main measurements. A product’s name or a phrase such as “energy-efficient glass” does not give you the same comparison.

U-factor: How readily heat passes through

A lower U-factor means better insulating performance. For example, a window rated 0.25 has a lower rate of heat transfer than one rated 0.30 under the rating conditions. These numbers are an illustration, not a recommended target for every home.

Ask whether a quoted number is the certified whole-window U-factor. A center-of-glass figure leaves out other parts of the assembly and is not an equivalent comparison.

SHGC: How much solar heat gets through

Solar heat gain coefficient runs from 0 to 1. Lower values mean less solar heat enters through the window. That makes SHGC especially worth discussing for a room that becomes uncomfortable in direct sun.

U-factor and SHGC answer different questions. Two products can have the same U-factor and different SHGC values. Ask your installer to explain both numbers rather than choosing from one alone.

Visible transmittance: How much daylight enters

Visible transmittance (VT) also runs from 0 to 1, with higher values admitting more visible light. Consider it alongside SHGC if you want to manage solar heat while keeping a room bright. The NFRC label overview explains how these measurements work together.

What Low-E glass tells you

Low-E means low emissivity. A thin coating on the glass helps control heat transfer. The U.S. Department of Energy’s consumer window guide explains how coatings, multiple panes, gas fills, frames, and spacers contribute to window performance.

“Low-E” by itself does not tell you the window’s U-factor, SHGC, or daylight level. Coatings and glass configurations can produce different results. Compare the finished product’s ratings, then ask to see a sample of the proposed glass so you can discuss its appearance.

Check the climate zone for your Georgia county

ENERGY STAR certification uses NFRC ratings and climate-specific performance requirements. Use the ENERGY STAR Climate Zone Finder, selecting Georgia and your county, before comparing certified options.

Then confirm that the exact product and glass package in the proposal qualify for that location. The current ENERGY STAR product criteria are a better reference than a general claim that an entire brand is energy efficient.

Match the conversation to each room

Window direction and shade matter. ENERGY STAR’s window buying guidance highlights solar heat control for sunny exposures, including west-facing windows that receive afternoon sun.

Before an appointment, make a short room-by-room list:

  • Sunny living room: Note when direct sun reaches the seating area and whether heat, glare, or both are the concern.
  • Shaded bedroom: Record comfort problems and whether keeping natural light is a priority.
  • Kitchen or office: Note the times you use the room and any blinds you regularly close.

Bring those observations to the product discussion. They help turn a general request for “better windows” into questions about the choices that suit each opening.

Use this checklist when comparing proposals

  • Write down the manufacturer, product line, operating style, and glass package for each option.
  • Request the certified whole-window U-factor, SHGC, and VT for the proposed configuration.
  • Confirm ENERGY STAR certification for your county when comparing certified products.
  • Ask why the recommended glass package fits the room’s sunlight and your priorities.
  • Ask what the installation includes and how the crew will follow the manufacturer’s instructions.

Installation deserves its own discussion. DOE cautions that even efficient windows can leave a home drafty or develop moisture problems when installed incorrectly. Product ratings are useful comparison tools, but they do not verify the quality of a particular installation.

Plan your next step

If you are still deciding whether replacement is appropriate, start with our guide to when to replace your windows. When you are ready to compare products, explore MR Premium Windows’ window styles and options and keep the rating checklist beside each proposal.

This guide provides general product-selection information. An assessment of your home and the specific window configuration is needed to make a recommendation.