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Calculate solar heat gain through windows
In Climate Zone 4, solar heat control (low SHGC) is most important for windows.
Climate Zone
4
Electricity
$0.11/kWh
Labor Costs
85% avg
Calculate how much solar heat enters through your windows
Calculate area for windows facing the same direction
Tennessee is in Climate Zone 4 - Mixed-Humid/Mixed-Dry (balanced heating and cooling). Homes here typically have higher cooling demands than heating.
Solar gain through windows depends on several factors:
In hot climates, aim for 0.25 or lower. In cold climates, 0.35-0.40 on south windows helps with passive heating. In mixed climates, 0.25-0.30 is typical. West-facing windows in any climate benefit from low SHGC.
Yes, but there are tradeoffs. Low-E coatings that improve U-value also reduce SHGC. Passive solar approaches use high-SHGC south windows with very good U-values and low-SHGC windows on other orientations.
Exterior shading (awnings, pergolas, shade screens) is most effective. Interior blinds and shades help less because heat is already inside. Window film can reduce SHGC but also affects visible light.
Yes. West-facing windows can account for up to 25% of summer cooling load due to intense afternoon sun. South windows in cold climates can provide 10-20% of heating needs through passive solar gain.