Modern bi-fold doors with thermally broken aluminum frames and low-E glazing perform comparably to fixed windows of the same size. The NFRC rates the thermal performance of every certified door system. For hot climates, specify a SHGC of 0.25 or lower to control solar heat gain per ENERGY STAR climate zone criteria. For cold climates, prioritize a low U-factor (0.30 or below). ENERGY STAR certification confirms the system meets the DOE’s minimum performance thresholds for your climate zone.