Estimate window film needed and solar heat savings.
Window film is judged on total solar energy rejection, which is the share of solar heat it stops rather than how dark it looks — modern spectrally selective films reject 50% or more while staying nearly clear. To estimate the saving, start from the fact that windows are typically responsible for around 35% of a home's cooling load, then apply the film's rejection figure to that share. Film area is the glazing area plus about 10% for trimming. The payback depends heavily on climate and orientation: on south and west glass in a hot climate a three to five year payback is realistic, while north-facing windows in a mild climate may never pay back on energy alone, though glare and fabric fading are often the real reason people fit it.
Window Tint Savings
Film area = windows x width x height / 144 x 1.1; saving = annual cooling cost x 35% x rejection%; payback = film cost / annual saving
Applying film to sealed double-glazed units can void the glazing warranty and, on some glass types, cause thermal stress cracking. Check the glass manufacturer's guidance and any local or HOA restrictions before installation.
Not necessarily. Spectrally selective films reject most of the near-infrared while passing visible light, so a nearly clear film can outperform a dark one — compare TSER, not visible light transmission.
West-facing first, then south, then east. North-facing glass in the northern hemisphere receives little direct sun and rarely justifies the cost on energy grounds alone.