SHGC & solar-heat-gain reference
What Solar Heat Gain Coefficient (SHGC) to target for your climate — low in the South to reject heat, higher in the North to capture free winter sun.
For Mixed climate, target an SHGC of about 0.30. SHGC is the fraction of solar heat that gets through (0–1); pick low in the South, higher in the North to capture free solar gain — the exact number is NFRC-rated on the label.
Calculator inputs
SHGC is the fraction of the sun’s heat that passes through a window, from 0 (blocks it all) to 1 (lets it all through). It is the second big NFRC number after U-factor, and unlike U-factor there is no single “lower is better” answer — the right SHGC depends on whether solar gain helps or hurts your energy bill.
In hot, cooling-dominated climates you want a low SHGC (~0.23 or less) so the window rejects solar heat and your air conditioner works less. In cold, heating-dominated climates a higher SHGC (~0.40+) on south- and east-facing glass captures free passive-solar warmth in winter. Mixed climates sit in between and often tune SHGC by orientation.
Formula
SHGC is a measured ratio, not a formula — it is read straight off the NFRC label. The planning targets are:
Cooling climate → SHGC ≤ ~0.23 · Mixed → ~0.25–0.40 · Heating climate → ~0.40+
Worked example
A homeowner in Phoenix (hot, cooling-dominated) should target SHGC ≈ 0.23 to cut summer solar heat. A homeowner in Minneapolis (cold, heating-dominated) can choose SHGC ≈ 0.42 on sunny elevations to bank free winter sun, while still keeping U-factor low so that heat does not leak back out at night.
Reading SHGC in the real world
Orientation matters more than a single house-wide number. North-facing glass sees little direct sun, so its SHGC barely affects the bill; west-facing glass drives late-afternoon cooling load, where a low SHGC pays off most. Low-E coatings and gas fills are how manufacturers hit a target SHGC without going dark — see the low-E & gas-fill reference. SHGC and visible light (VT) trade off, so a very low SHGC can dim a room; check both on the label.
Reference table
| Climate goal | Target SHGC | Why |
|---|---|---|
| Hot / cooling-dominated (South) | ~0.23 | Low SHGC ≤ ~0.23 to reject solar heat |
| Mixed climate | ~0.30 | Moderate SHGC ~0.25–0.40 |
| Cold / heating-dominated (North) | ~0.42 | Higher SHGC ~0.40+ to capture free solar gain |
Labeled planning typicals — the exact SHGC is NFRC-rated on the product label; confirm the ENERGY STAR / IECC requirement for your zone.
Frequently asked questions
What is a good SHGC for windows?
It depends on climate. In hot, cooling-dominated regions aim for SHGC ≤ 0.23; in cold, heating-dominated regions a higher SHGC (~0.40+) captures free winter sun. Mixed climates land around 0.25–0.40.
Is a lower SHGC always better?
No. A low SHGC helps in the South by rejecting heat, but in a cold northern climate a slightly higher SHGC on sunny elevations lowers your heating bill. Match SHGC to whether cooling or heating dominates your year.
What is the difference between SHGC and U-factor?
U-factor measures conductive heat loss (lower is always better); SHGC measures how much solar heat comes through (the ideal value depends on climate). A good window controls both. Convert U to R with the U-factor ↔ R-value converter.
Does a low SHGC make a room darker?
It can. SHGC and Visible Transmittance (VT) are related but separate; spectrally selective low-E coatings cut heat while keeping light, so check VT on the label too — see the VT & condensation reference.