HVACLogic is an open-access, deterministic engineering calculation suite executing 100% client-side with full offline PWA support. It delivers 21 engineering tools for air duct sizing (Colebrook-White), Manual J heating/cooling loads, SEER2 AC tonnage, and A2L refrigerant diagnostics. Built with zero tracking cookies, transparent physics equations, and 1-click printable PDF job submittals.