Low-E Coating Calculator

This calculator estimates how a Low-E coating changes window performance: U-factor reduction, SHGC, a light-to-solar-gain daylight ratio, and separate winter and summer performance scores tied to the coating's surface position. Coating Emissivity is the only input U-Factor Reduction responds to -- the formula measures the coating's emissivity against an uncoated-glass baseline of 0.84, raised to the one-quarter power, so a lower emissivity produces a larger reduction, while Solar Transmittance and Visible Transmittance play no part in that particular result. SHGC Value comes straight from Solar Transmittance with a small fixed offset added, and the Light-to-Solar Gain Ratio then measures Visible Transmittance against that SHGC Value, so more visible light for the same solar gain lifts the daylight ratio.

Winter Performance and Summer Performance are never the same underlying score, though -- Winter Performance always tracks Coating Emissivity (1 minus emissivity) and Summer Performance always tracks Solar Transmittance (1 minus solar transmittance), and neither one ever responds to the other's driver. What Coating Position changes is which of those two scores gets full 100% weighting versus a reduced 80% weighting: Surface 2, the inner face of the outer pane and the pick for heating climates, gives Winter Performance the full weighting while Summer Performance is held to the reduced 80%; Surface 3, the outer face of the inner pane and the pick for cooling climates, flips that so Summer Performance gets the full weighting and Winter Performance drops to the reduced 80%. These outputs are simplified relative scores meant for comparing coating options against each other, not certified NFRC ratings.