What U-factor and SHGC do windows need in Georgia?

In Climate Zone 3, which includes Henry County, the Georgia-amended energy code caps windows at a 0.35 U-factor and a 0.27 solar heat gain coefficient, and skylights at a 0.55 U-factor. The 0.27 SHGC is Georgia's own amendment rather than the base national figure, so a window spec'd to a national table can miss it.

What is SHGC and why does it matter more here than U-factor?

SHGC is the share of the sun's heat a window lets through, on a scale of 0 to 1, and the Department of Energy puts it plainly: the lower the SHGC, the less solar heat the window lets in. In a state NOAA describes as having long, hot and humid summers, keeping sun heat out of the house does more work than slowing heat loss, which is what U-factor measures.

Do replacement windows have to meet the energy code?

Yes, on the reading of the code as published. Georgia's amendments to the existing-buildings chapter touch heating, cooling and ducts, leaving the replacement fenestration section as written, and that section requires replacement units to meet the U-factor and SHGC for the climate zone, with an area-weighted average allowed across several units. That is a two-step reading of two documents, so confirm it with your permit office on a specific job.

Is ENERGY STAR better than code?

Yes, it is tighter, and it is voluntary. ENERGY STAR puts Henry County in its South-Central climate zone, where a qualifying window needs a U-factor of 0.28 or lower and an SHGC of 0.23 or lower. Its Most Efficient tier goes further again, at a U-factor of 0.20 or lower with the same 0.23 SHGC. Code is 0.35 and 0.27, so both tiers sit well inside it.

Is triple glazing worth it in Georgia?

Rarely. Triple glazing earns its price in cold climates by driving the U-factor down, and the Georgia problem is sun heat rather than heat loss. The money usually goes further on a low-E coating tuned for a low SHGC, a good spacer and an installation that actually seals, than on a third pane of glass.

Where do I find these numbers on a window?

On the NFRC label stuck to the glass of every new unit. It lists U-factor and SHGC as its two headline figures, plus visible transmittance and air leakage. Check it before the sticker is peeled off, because after that you are relying on the paperwork matching what was fitted.

Energy Efficient Windows McDonough GA

The two numbers Georgia sets for a new window

A replacement window in Henry County has to come in at 0.35 or lower on U-factor and 0.27 or lower on SHGC. Henry County confirms Climate Zone 3 on its own residential energy code compliance affidavit, and those are the figures the Georgia-amended energy code sets for that zone, with skylights allowed up to 0.55.

What has to be met, and what goes beyond it

Figure	Georgia code, Zone 3	ENERGY STAR, South-Central	What it measures
Window U-factor	0.35 maximum	0.28 maximum	Heat moving through the whole unit, frame included. Lower is better.
Window SHGC	0.27 maximum	0.23 maximum	Share of the sun's heat let through, 0 to 1. Lower is better here.
Skylight U-factor	0.55 maximum	Set separately by product type	Same as U-factor, measured on a sloped unit.
Air leakage	Not set in this table	0.3 cfm per sq ft or lower	Air passing through the assembly under test pressure.
Opaque door U-factor	Not set in this table	0.17 or lower	Heat through a solid entry door.

Swipe the table sideways to see every column →

Code figures: Georgia amendments to the International Energy Conservation Code, Table R402.1.2, Climate Zone 3. ENERGY STAR figures: version 7.0, effective October 23, 2023, for the South-Central climate zone, which is the zone ENERGY STAR's own finder returns for Henry County, Georgia.

Three tiers, one address

Everything above collapses into three lines. The first is a legal requirement, the second and third are voluntary labels a manufacturer earns. ENERGY STAR's own climate zone finder places Henry County in its South-Central zone, which is what sets the second row.

The three standards a window here can be measured against

Standard	U-factor	SHGC	Status
Georgia code, Climate Zone 3	0.35 or lower	0.27 or lower	Required
ENERGY STAR, South-Central zone	0.28 or lower	0.23 or lower	Voluntary label
ENERGY STAR Most Efficient	0.20 or lower	0.23 or lower	Voluntary, top tier

Swipe the table sideways to see every column →

Code figures from the Georgia amendments to the energy code for Climate Zone 3, with the 0.27 SHGC being Georgia's own amendment. ENERGY STAR figures from its version 7.0 criteria for the South-Central zone, which is the zone its climate zone finder returns for Henry County, Georgia. Read October 2026.

The practical reading: a window that merely clears code can be a third less efficient on U-factor than one carrying an ENERGY STAR label for this zone, and more than half as efficient as a Most Efficient unit. None of that makes a code-compliant window a bad window. It does mean the words energy efficient on a quote are worth nothing without the two numbers beside them.

Why SHGC does more work than U-factor here

U-factor is about keeping heat in on a cold night. SHGC is about keeping the sun's heat out on a hot afternoon, and Georgia has far more of the second problem. NOAA's state climate summary describes long, hot and humid summers, with the Atlanta area averaging seven days a year above 95 degrees and summers that have warmed since 1900. The Department of Energy's own guidance is one sentence long: the lower the SHGC, the less solar heat the window lets in.

A useful way to see the difference: ENERGY STAR's southern criteria cap SHGC at 0.23, while its northern criteria set a minimum rather than a cap, because up there the winter sun through the glass is free heat. A window specified for Ohio is the wrong window for Henry County, and it will still carry an ENERGY STAR logo.

Window styles sold in McDonough GA, from double hung to awning, shown side by side — Style changes how much of a window opens, which changes air leakage as much as it changes the view. Our own diagram.

What the glass package actually contains

Behind those two numbers sit a handful of choices your quote should name:

Low-E coating: a microscopically thin metal layer on the glass. The tuning decides how much solar heat gets through, which is where your SHGC number comes from.
Gas fill: argon between the panes slows heat transfer and lowers U-factor.
Spacer: what holds the panes apart at the edge. A warm-edge spacer cuts the cold line around the glass, and the spacer seal is the part that fails on a fogged unit.
Pane count: two is standard in Georgia, three buys U-factor you mostly do not need here.
Frame material: vinyl, fiberglass, aluminum and wood all conduct heat differently, which is why U-factor is measured on the whole unit, not the glass.

Low-E does something else worth knowing about in a bright climate. The Department of Energy says low-E coatings can protect household furnishings from UV-induced fading by as much as 75 percent. If a south-facing room has bleached a rug or a hardwood floor, that is the number to bring up.

A white double-hung window with grids in a red brick wall between blue shutters — The NFRC label with these numbers on it is stuck to the glass of every new unit until somebody peels it off. Stock photo, not a local job.

Installation decides whether the numbers survive

A new energy efficient window for a McDonough GA house set and flashed in the opening, its rating label still on the glass — The rating label stays stuck to the glass until the job is signed off, which is your chance to read the U-factor and SHGC on the unit you were actually sold. Photo: ArmchairBuilder.com, CC BY 2.0, via Flickr.

Georgia's own code amendments make the point in their commentary: air infiltration accounts for substantial heat loss, heat gain and moisture migration in a building, and proper sealing around all doors, windows and other envelope penetrations is as important to code compliance as insulation R-values and component U-factors. The Department of Energy says the same thing from the other direction: even the most energy-efficient windows can result in a drafty house and moisture condensation if they are not properly installed.

Which is to say a 0.27 SHGC unit fitted badly performs worse than a plainer unit fitted well. Window installation covers what belongs in the gap between the frame and the framing.

What efficiency is worth at resale

The Department of Energy's window guide puts the resale recovery on a window project at about 78 percent of the cost. That is a national figure rather than a Henry County one, and it is a useful counterweight to both the sales pitch that windows pay for themselves and the assumption that they are money thrown at the wall. For what the job itself costs here, see the McDonough window replacement cost guide.

Energy Efficient Windows in McDonough, GA