“Low-E” is one of the most common terms in window shopping—and one of the easiest to oversimplify.
A Low-E coating can improve thermal and solar performance, but Low-E alone does not tell you how a complete impact-window assembly will perform in a Florida home.
For a useful comparison, look at the NFRC ratings for the exact product and glass package, especially Solar Heat Gain Coefficient (SHGC) and U-factor.
What is Low-E glass?
Low-E means low emissivity.
The U.S. Department of Energy describes Low-E coatings as microscopically thin metallic or metallic-oxide layers applied to glass to control heat transfer. Depending on the coating and glazing design, Low-E can affect:
- U-factor
- Solar heat gain
- Visible light
- Overall glazing performance
Different Low-E coatings are designed for different climate goals. “Has Low-E” is therefore not a complete specification.
What is SHGC?
Solar Heat Gain Coefficient measures how much solar heat a complete window, door, or skylight allows into the building.
The value is expressed between 0 and 1.
- A lower SHGC means less solar heat is admitted.
- A higher SHGC means more solar heat is admitted.
The Department of Energy notes that lower SHGC is generally useful in warm climates where reducing unwanted solar heat can reduce cooling loads.
That makes SHGC particularly relevant in Florida, but it should still be considered with daylight, glass appearance, orientation, shading, and the complete product.
What is U-factor?
U-factor measures heat transfer through the fenestration product.
- A lower U-factor indicates lower heat transfer.
- A higher U-factor indicates more heat transfer.
Do not confuse U-factor with the R-value language commonly used for wall insulation. They describe thermal performance differently.
What does the NFRC label add?
NFRC provides standardized, third-party energy-performance ratings for windows, doors, skylights, and related fenestration products.
Depending on the product, the label can include:
- U-factor
- Solar Heat Gain Coefficient
- Visible Transmittance
- Air Leakage
- Condensation-related rating information
The value of the label is comparability.
Instead of relying on phrases like “high performance,” “energy glass,” or “premium Low-E,” you can compare certified ratings for the actual configuration.
Does impact glass automatically mean energy efficient?
No.
Impact resistance addresses one set of performance requirements. Energy performance addresses another.
An impact window may use laminated glass alone, laminated insulating glass, Low-E coatings, tints, different spacers, different frame materials, or other combinations.
Two impact windows can both satisfy impact requirements and still have different NFRC ratings.
Our broader guide on impact-window energy efficiency explains the distinction.
Is a lower SHGC always better?
Not in every design decision.
In a hot Florida climate, reducing unwanted solar heat is often important. But a homeowner may also care about natural daylight, glass color, exterior appearance, room orientation, shading, privacy, and HOA requirements.
Visible Transmittance helps describe how much visible light passes through the product. A good selection balances the metrics that matter for the project rather than chasing one number in isolation.
What about UV protection?
Low-E, laminated interlayers, tints, and other glazing features can affect ultraviolet transmission, but UV performance should be verified from the actual product documentation.
Do not assume that every Low-E coating or every impact laminate blocks the same percentage of UV.
See our impact windows and UV protection guide for that separate question.
What should you ask for in a quote?
If energy performance is a priority, ask for:
- Exact manufacturer and series
- Exact glass package
- Whether it is insulating glass
- Low-E coating designation
- NFRC U-factor
- NFRC SHGC
- Visible Transmittance, if daylight matters
- Air Leakage rating, if available
- Product approval for the impact/wind application
- Confirmation that the quoted configuration matches the documentation being shown
Do not accept a rating from a different product family as proof of the one being quoted.
Can Low-E guarantee a specific power-bill reduction?
No.
Actual household energy use depends on existing windows, home size, orientation, insulation, roof, HVAC efficiency, thermostat settings, air leakage, shading, occupancy, weather, and utility rates.
Energy ratings help compare products. They are not a promise of a specific monthly savings amount.
Frequently asked questions
Is Low-E the same as tinted glass?
No. A Low-E coating and a tint can both affect solar performance, but they are different glazing technologies.
What is the most important rating for Florida?
There is no single universal number. SHGC is especially relevant to solar heat gain in warm climates, while U-factor remains important for overall heat transfer.
Does every impact window have an NFRC label?
Do not assume it. Ask for certified energy-performance information for the exact product and configuration.
Does Low-E make impact windows stronger?
Low-E is an energy-performance coating, not a substitute for impact testing, design-pressure approval, or correct installation.
Authoritative sources
- U.S. Department of Energy — Window Types and Technologies
- U.S. Department of Energy — Purchasing Energy-Efficient Residential Windows, Doors, and Skylights
- NFRC — Residential Product Certification
- NFRC — Window energy-performance ratings
- Florida Statutes §553.842
The bottom line
For Florida impact windows, Low-E is a feature; the NFRC ratings are the comparison tool.
Look at SHGC, U-factor, visible light, air leakage, and the exact glass configuration alongside impact and design-pressure documentation.
AA Glass & Windows can help compare impact-window glass packages for protection, comfort, and energy-performance goals. Request a free estimate to review your options.