Solar heat gain in Phoenix: how Energy Shield windows compare to the 0.25 code limit
Every current Energy Shield window and sliding glass door has an NFRC-certified whole-window SHGC at or under the 0.25 maximum the energy code sets for the Phoenix area. With our LoE³-340+ glass package, every window is between 0.14 and 0.16, in both the ES3000 and ES7000 series.
What SHGC is, and why it is the number to watch in Phoenix
The solar heat gain coefficient (SHGC) is the share of the sun's heat that gets through a window, from 0 to 1. Lower lets less heat in. In a climate where Phoenix ran 113 days in a row at 100°F or hotter in 2024, the heat coming through the glass is what your air conditioner fights. That is why we treat SHGC as the most important window number in Arizona.
What the code says
- The International Energy Conservation Code (IECC) residential prescriptive path sets a maximum SHGC of 0.25 for climate zones 0 to 3. The Phoenix metro is climate zone 2B.
- Arizona has no statewide energy code. Each city adopts its own edition. The City of Phoenix enforces the 2024 IECC, with amendments, as of August 1, 2025 (Ordinance G-7397). Its amendments do not change the window SHGC table.
- Other Valley cities may be on other editions; the 0.25 SHGC maximum for zones 2 and 3 is the same in the 2012 through 2024 editions.
How every Energy Shield window and door rates
NFRC-certified whole-window U-factor, SHGC, and visible light for each product and glass package, without grids. Glass: Cardinal LoE³-340+ (with an LoE-i89 inner pane) or LoE³-366, argon, double-strength 3 mm glass. Both series, ES3000 and ES7000, carry the same ratings. Grids lower the SHGC and visible light a little; the dataset has both.
| Series | Type | Glass | SHGC | Under the 0.25 maximum by | U-factor | Visible light |
|---|---|---|---|---|---|---|
| ES3000 and ES7000 | Picture window | LoE³-340+ | 0.16 | 0.09 | 0.21 | 0.34 |
| ES3000 and ES7000 | Picture window | LoE³-366 | 0.25 | 0.00 | 0.25 | 0.58 |
| ES3000 and ES7000 | Single hung | LoE³-340+ | 0.14 | 0.11 | 0.24 | 0.31 |
| ES3000 and ES7000 | Single hung | LoE³-366 | 0.22 | 0.03 | 0.28 | 0.52 |
| ES3000 and ES7000 | Horizontal slider | LoE³-340+ | 0.14 | 0.11 | 0.24 | 0.31 |
| ES3000 and ES7000 | Horizontal slider | LoE³-366 | 0.22 | 0.03 | 0.28 | 0.52 |
| 3800 | Sliding glass door | LoE³-366 | 0.23 | 0.02 | 0.27 | 0.53 |
| 5800 | Sliding glass door | LoE³-366 | 0.19 | 0.06 | 0.29 | 0.44 |
Download this table as CSV from our performance ratings dataset.
Reading the table
- Lowest SHGC: the single hung and horizontal slider with LoE³-340+ glass, at 0.14, in both series.
- The trade-off: the LoE³-340+ package lets in far less heat, and also less visible light (0.31 to 0.34) than the LoE³-366 package (0.52 to 0.58 in windows). Rooms that need more daylight may suit LoE³-366; rooms that face the afternoon sun may suit LoE³-340+.
- U-factor (heat moving through the whole window, lower is better) runs 0.21 to 0.28 for windows and 0.27 to 0.29 for sliding glass doors.
- Sliding glass doors come with LoE³-366 glass, at an SHGC of 0.19 to 0.23.
ENERGY STAR is stricter than the code
ENERGY STAR version 7.0 sets SHGC at 0.23 or lower for windows and glass doors in its South-Central and Southern zones. Every LoE³-340+ window is under that, and every LoE³-366 window and sliding glass door is at or under it except the picture window, at 0.25 (0.22 with grids). Meeting the number is not the same as being ENERGY STAR certified; certification is per product.
The glass alone (not the whole window)
Cardinal rates the LoE³-340+ glass itself, measured at the center of the glass in a dual-pane unit with an LoE-i89 inner pane and argon:
| LoE³-340+ / LoE-i89, argon (center-of-glass) | Value |
|---|---|
| SHGC | 0.17 |
| U-factor | 0.20 |
| Visible light | 38% |
| UV let through | 2% |
Center-of-glass numbers measure the glass only, without the frame and the glass edge. The whole-window numbers in the table above include both, which is why they differ (an SHGC of 0.14 to 0.16 for the whole window against 0.17 for the glass alone). The code limit applies to the whole window.
For sound, the glass is rated STC 31 / OITC 26 (3 mm glass, about 1/2-inch air space). That is the glass alone; a whole window usually rates a little lower.
Questions
What SHGC do I need for windows in Phoenix? The IECC sets a maximum SHGC of 0.25 for climate zones 0 to 3, which include the Phoenix metro. Lower lets less solar heat in.
Is SHGC 0.25 a minimum or a maximum? A maximum. A window's SHGC must be 0.25 or lower under the IECC prescriptive path for zones 0 to 3.
Which Energy Shield window has the lowest SHGC? The single hung and the horizontal slider with LoE³-340+ glass, at a whole-window SHGC of 0.14, in both the ES3000 and ES7000 series.
Does Arizona have a statewide energy code? No. Cities adopt their own. Phoenix enforces the 2024 IECC with amendments as of August 1, 2025.
Sources
- ICC, 2024 IECC Table R402.1.2. PNNL Building America Solution Center, IECC fenestration requirements 2009 to 2021.
- City of Phoenix, 2024 IECC amendments, Ordinance G-7397, effective August 1, 2025.
- U.S. DOE, Arizona energy code status.
- ENERGY STAR, residential windows and doors criteria, version 7.0.
- Cardinal Glass Industries, LoE³-340+ datasheet (2025).
- Cardinal IG, Technical Service Bulletin IG09 (acoustics).
- National Weather Service Phoenix.
More on low-E glass
Have you noticed your utility bills rising or have begun to feel excessive temperatures near your windows? One of the most effective ways to solve both issues is to install Low-E windows. Since 1996 Energy Shield Window & Door Company has been installing Low-E coating glass windows for customers seeking greater energy efficiency. So, what makes these energy efficient windows so remarkable, and what type of coatings work best in our Arizona climate? We’ll break down the answers and invite you to schedule a free consultation with us to see samples of this high-performance glass and further discuss your needs.
Low-E Coating Glass: What It Is and It's Role in Energy Efficient Windows
Low-E stands for low-emissivity, and it’s a microscopically thin coating for glass designed to minimize ultraviolet and infrared light penetration into indoor spaces.
Low-E high-performance glass works by reflecting interior temperatures back inside during colder months and reduces the amount of radiant heating lost through the glass. In warmer months, Low-E glass deflects the sun to maintain indoor temperatures and reduce energy use.
How High-Performance Glass Efficiency is Determined
Low-E coating glass efficiency is measured by four primary factors:
U-Value - Measures how much heat loss the window allows
Solar Heat Gain Coefficient - The amount of solar radiation that is absorbed or admitted through the glass
Visible Light Transmittance - Measures the amount of light transfer through the glass.
Light to Solar Gain - Represents visible light transmittance along with the Solar Heat Gain Coefficient rating
Our Energy Shield Window & Door Company professionals can help determine the right Low-E windows for your project.
Types of Low-E Coating Glass
Passive Low-E coatings are crafted using a pyrolytic process to create a hard coating. Through a special process, the coating is fused to the surface to create a strong, durable bond. These are best for cold climates in general, because they permit certain levels of infrared energy to pass through.
Solar Control Low-E coatings are known as ‘soft-coat’ and are applied in a vacuum chamber to pre-cut glass and then sealed. Soft-coat Low-E windows offer superior heat and UV ray protection and offer superior energy efficiency in hot climates.
Choosing the Best Low-E Coating for Energy Efficient Windows in Arizona
Our temperatures in Arizona can reach high levels, especially during the summer months. While both Low-E options increase efficiency and improve indoor comfort levels, here at Energy Shield Window & Door Company our pros tend to recommend soft-coat Low-E coatings for those in the southern part of the state.
However, those living in more mountainous regions might get better results with a hard-coat Low-E high-performance glass. Our industry-certified technicians can help you decide and will also discuss any current specials for window installations in Arizona.
Why Choose Energy Shield Window & Door Company?
Replacing old windows with energy-efficient ones with Low-E coating glass can save you money by helping maintain indoor temperatures and by reducing heating and cooling transference through the glass. Here at Energy Shield Window & Door Company, we manufacture top-quality energy efficient windows with high-performance glass coatings designed specifically for our Arizona climate. Every service and product we provide is crafted and installed by factory-trained, industry certified technicians. Contact us online or call us today at (623) 231-2451 for a complimentary estimate on your window project.
Written by Juan Valles, co-owner, Energy Shield Window & Door Company. Updated October 29, 2026.
