How to Build a Heat Pump Calculator

interface HeatPumpInput {
  squareFootage: number;
  ceilingHeightFt: number;
  insulationQuality: 'poor' | 'average' | 'good' | 'excellent';
  climateZone: 1 | 2 | 3 | 4 | 5 | 6 | 7;
  windowSqFt: number;
  windowType: 'single' | 'double' | 'triple';
  sunExposure: 'north' | 'south' | 'east' | 'west' | 'mixed';
  occupants: number;
  }

  interface HeatPumpResult {
  heatingLoadBTU: number;
  coolingLoadBTU: number;
  recommendedTons: number;
  recommendedBTU: number;
  systemSuggestions: string[];
  }

  const BTU_FACTOR = { poor: 50, average: 35, good: 25, excellent: 18 };
  const CLIMATE_FACTOR = { 1: 0.85, 2: 0.9, 3: 1.0, 4: 1.1, 5: 1.25, 6: 1.4, 7: 1.55 };
  const WINDOW_BTU_PER_SQFT = { single: 100, double: 50, triple: 30 };
  const SUN_FACTOR: Record<string, number> = {
  south: 1.10, west: 1.10, east: 1.02, north: 0.95, mixed: 1.0
  };

  function calculateHeatPumpSize(input: HeatPumpInput): HeatPumpResult {
  const baseBTU = input.squareFootage * BTU_FACTOR[input.insulationQuality];
  const ceilingFactor = input.ceilingHeightFt / 8;
  const climateFactor = CLIMATE_FACTOR[input.climateZone];
  const windowLoad = input.windowSqFt * WINDOW_BTU_PER_SQFT[input.windowType];
  const sunMult = SUN_FACTOR[input.sunExposure];
  const occupantLoad = Math.max(0, input.occupants - 2) * 400;

  const rawLoad = (baseBTU * ceilingFactor * climateFactor * sunMult) + windowLoad + occupantLoad;
  const heatingLoad = Math.round(rawLoad * 1.1); // 10% safety margin
  // Cooling load is typically 70-90% of heating load in northern zones, higher in southern
  const coolingRatio = input.climateZone <= 2 ? 1.1 : input.climateZone <= 4 ? 0.85 : 0.75;
  const coolingLoad = Math.round(rawLoad * coolingRatio);

  const dominantLoad = Math.max(heatingLoad, coolingLoad);
  const tons = Math.ceil(dominantLoad / 12000 * 2) / 2; // round up to nearest 0.5 ton

  const suggestions: string[] = [];
  if (tons <= 2) suggestions.push('Single-zone mini-split (18,000-24,000 BTU)');
  if (tons > 2 && tons <= 3) suggestions.push('Multi-zone mini-split or small ducted system');
  if (tons > 3 && tons <= 5) suggestions.push('Central ducted heat pump (3-5 ton)');
  if (tons > 5) suggestions.push('Multiple systems or commercial-grade heat pump');
  if (input.climateZone >= 5) suggestions.push('Consider cold-climate heat pump (rated to -15F)');
  if (input.climateZone >= 6) suggestions.push('Supplemental heating source recommended for extreme cold');

  return {
    heatingLoadBTU: heatingLoad,
    coolingLoadBTU: coolingLoad,
    recommendedTons: tons,
    recommendedBTU: tons * 12000,
    systemSuggestions: suggestions
  };
  }