Best Windows for Hot, Humid Climates: SHGC, U-Factor and What Else to Check

In a hot, humid climate, the most important window rating is the solar heat gain coefficient (SHGC), and lower is better. ENERGY STAR advises homeowners in the South to "look for lower SHGC levels (0.23 and less)." Under ENERGY STAR Version 7.0, windows in the Southern zone need an SHGC of 0.23 or lower and a U-factor of 0.32 or lower. In the South-Central zone, the limits are SHGC 0.23 or lower and U-factor 0.28 or lower. After SHGC, compare U-factor, visible transmittance (VT) and air leakage. None of the energy ratings measures humidity, so installation and water resistance matter as well.

Updated: October 2026.

Why SHGC comes first in hot climates

SHGC "measures the amount of solar heat [that] can enter a home through a window," according to the National Fenestration Rating Council (NFRC). It runs from 0 to 1, and a lower number means less solar heat comes in. The US Department of Energy's Federal Energy Management Program (FEMP) puts it simply: "In warm climates, buy or specify products with low SHGCs to reduce unwanted heat gain." FEMP adds that windows with low-E coatings, "especially spectrally selective coatings, are effective at reducing summer heat gain."

U-factor still matters. NFRC says it "measures the amount of heat inside your home that can escape through a window," and lower is better. ENERGY STAR sets a U-factor limit in the Southern and South-Central zones as well as an SHGC limit.

ENERGY STAR limits for warm zones

Version 7.0 took effect on October 23, 2023. To qualify, a window needs NFRC-certified U-factor and SHGC ratings that meet the limits for its zone. Windows must also have air leakage of 0.3 cfm/ft² or less. ENERGY STAR assigns zones by state and county, and in some places by ZIP code, so look yours up with the ENERGY STAR climate zone finder instead of assuming.

The other ratings to compare

NFRC ratings are calculated for standard conditions and a standard product size, and NFRC does not recommend products. Use the ratings to compare windows with each other, not to predict exact bills.

Humidity: what the ratings don't tell you

No NFRC rating measures humidity. Two other checks are worth making in a humid, stormy climate:

• Air leakage. FEMP notes that "air leakage through fenestration can be a significant source of heat loss or gain in a building." Air leakage is optional on the NFRC label, so if it isn't shown, check whether the product carries a certification label that covers it, as ENERGY STAR allows.
• Water penetration resistance. The Fenestration and Glazing Industry Alliance (FGIA) explains that a Performance Grade (PG) under the North American Fenestration Standard (AAMA/WDMA/CSA 101/I.S.2/A440) includes air infiltration, water penetration and structural tests, not just a design pressure (DP) rating. FGIA advises checking that a product's certification shows the full PG. Products can be searched in the FGIA Certified Products Directory.

For moisture in the wall opening around a window, see why mold grows around window reveals.

In Florida, the building code requires exterior glazed openings in wind-borne debris regions to be protected from wind-borne debris (Florida Building Code, Residential, Section R301.2.1.2), either with impact-rated windows or with shutters. That is a structural requirement, separate from energy ratings. In any coastal area, ask your local building department what applies to your address.

How glass choices change the numbers

• Low-E coatings. FEMP notes that low-E coatings, especially spectrally selective ones, are effective at reducing summer heat gain. See low-emissivity (low-E) glass.
• Spacers and frames. NFRC U-factor ratings cover the whole product, including frame and spacer. See spacers and window energy efficiency.
• Orientation. The GlassBase window energy calculator lets you set the wall direction and shows how heating and cooling energy change for your ZIP code, so you can see whether a lower SHGC matters more on one side of the house than another.

Comparing two windows: a quick method

1. Find your ENERGY STAR zone and note the U-factor and SHGC limits above.
2. Ask each supplier for the NFRC-certified ratings of the exact product and glass package, and confirm them in the NFRC Certified Products Directory or the ENERGY STAR Product Finder.
3. Rule out anything above your zone's limits. Among the rest, prefer the lower SHGC for sun-exposed walls, and use VT to choose between options with similar SHGC.
4. Check air leakage and the FGIA performance grade.
5. Model your actual case. Enter your ZIP code, wall direction and glazing in the calculator and compare cooling and heating energy in kWh. The calculator's values are engineering estimates, not NFRC ratings. See how the simulator works.

To find companies that supply or install windows near you, browse window companies by city, for example Houston, New Orleans, Tampa or Miami. Terms are defined in the glossary.

Compare SHGC options for your ZIP code

Sources

• US EPA, ENERGY STAR, High Performing Windows or Storm Windows (SHGC 0.23 and less in the South)
• US EPA, ENERGY STAR, Residential Windows, Doors, and Skylights Version 7.0 (zone limits, air leakage, effective October 23, 2023) and climate zone finder
• US EPA, ENERGY STAR, Residential Windows, Doors and Skylights
• US DOE, FEMP, Purchasing Energy-Efficient Residential Windows, Doors, and Skylights (low SHGC in warm climates; spectrally selective low-E; air leakage)
• NFRC consumer guide, Window ratings (definitions, ranges, mandatory and optional ratings)
• FGIA, Understanding Fenestration Performance Classes