Every free HVAC load calculator I could find makes you pick one of five climate regions, which can put you 20°F off your real design condition. This one resolves your ZIP code to published 99%/1% design temperatures and tells you how closely it matched. Eight inputs, whole-house heating and cooling BTU plus tonnage. No account, no email gate. Same engine as the iOS/Android app, checked by an automated parity test. Block load only, and it says so.