The IECC Section 5 addresses mechanical system efficiency requirements. HVAC equipment must meet minimum efficiency ratings established by the U.S. Department of Energy. Air conditioners and heat pumps must meet Seasonal Energy Efficiency Ratio (SEER) ratings ranging from 13-17 depending on climate, with higher efficiency in colder climates. Furnaces must meet Annual Fuel Utilization Efficiency (AFUE) ratings of 90 percent or higher. Boilers used for radiant heating and domestic hot water must meet minimum efficiency of 85-90 percent depending on application. Water heaters must meet Energy Factor (EF) ratings ranging from 0.60-0.90 depending on fuel type and size. High-efficiency condensing water heaters achieve EF ratings above 0.90. Heat pump water heaters with integrated desuperheaters can achieve efficiencies exceeding 2.0. Ductwork must be sealed with mastic or metal-backed tape (not cloth-backed tape) to prevent leakage. Ductwork located in conditioned space (attics or mechanical rooms) should be minimized, with outdoor units preferred. Ducts in attics or crawlspaces that are unconditioned must be insulated with minimum R-5 insulation. Supply and return ductwork must be balanced to deliver appropriate air flow to all spaces. Variable-frequency drives (VFDs) on fan motors modulate fan speed based on demand, reducing energy consumption. Heat recovery ventilation systems can reduce heating and cooling loads by recovering energy from exhaust air.