Energy Efficiency Requirements: For ENERGY STAR certification, product glazing shall have Emissivity and Solar Transmissions ratings certified by an approved third-party certification body at levels which meet or exceed the certification criteria described in the following table for a given climate zone.
ENERGY STAR Climate Zone
Air Leakage Requirements: For ENERGY STAR certification, products shall have Air Leakage ratings at levels which meet or exceed the certification criteria specified in the following table.
Air Leakage Rating
Exterior Storm Window
≤ 1.5 cfm/ft2
Interior Storm Window
≤ 0.5 cfm/ft2
Definitions of Performance Metrics
Emissivity: The relative ability of a surface to reflect or emit heat by radiation. Emissivity ranges from 0 to 1.
Solar Transmittance (Tsol): The ratio of transmitted radiant flux in the solar spectrum (300 nm to 2500 nm) to incident radiant flux in the solar spectrum.
Air Leakage: A measure of the rate of air passing through a material or assembly in the presence of an applied pressure difference, expressed in units of cfm/ft2.