{
  "id": "btu",
  "version": "f7954d9d51f3",
  "status": "published",
  "name": "BTU Calculator",
  "question": "How many BTU does my AC need?",
  "summary": "Computes the cooling capacity in BTU per hour for a room air conditioner from the room area, sun, people and kitchen use, by the ENERGY STAR sizing table.",
  "category": "construction",
  "url": "https://www.acalculator.org/construction/btu-calculator",
  "markdown": "https://www.acalculator.org/construction/btu-calculator.md",
  "kind": "function",
  "method": "capacity = table value for the area × (0.9 shaded, 1.1 very sunny) + 600 BTU/h for each person over 2 + 4,000 BTU/h for a kitchen",
  "assumptions": [
    "The table rows run from their lower area up to, not including, the next row’s; the last row includes 2,500 ft².",
    "The ENERGY STAR table is for room air conditioners in one room. It is not a load calculation for central air, which needs a full load calculation such as ACCA Manual J.",
    "The adjustments are applied in this order: sun first, as a percent of the table value, then people and kitchen as fixed amounts."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "area": {
        "title": "Room area",
        "description": "The floor area of the room to cool, from 100 to 2,500 square feet.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "area",
        "minimum": 9.290304,
        "maximum": 232.25760000000002
      },
      "sun": {
        "title": "Sun",
        "description": "How much sun the room gets.",
        "type": "string",
        "enum": [
          "shaded",
          "normal",
          "sunny"
        ]
      },
      "people": {
        "title": "People",
        "description": "How many people usually use the room.",
        "type": "integer",
        "minimum": 1,
        "maximum": 100
      },
      "kitchen": {
        "title": "Kitchen",
        "description": "The unit cools a kitchen.",
        "type": "boolean"
      }
    }
  },
  "outputs": {
    "btu": {
      "label": "Cooling capacity",
      "description": "The capacity to look for, in BTU per hour.",
      "format": "quantity",
      "unit": "BTUh"
    },
    "base": {
      "label": "From the area alone",
      "description": "The capacity the ENERGY STAR table gives for the room area, before adjustments.",
      "format": "quantity",
      "unit": "BTUh"
    },
    "tons": {
      "label": "Tons of cooling",
      "description": "The capacity ÷ 12,000 BTU per hour.",
      "format": "number"
    },
    "watts": {
      "label": "Cooling in watts",
      "description": "The capacity in watts of heat removed (not the power the unit draws).",
      "format": "quantity",
      "unit": "W"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "area": 18.580608,
      "sun": "normal",
      "people": 2,
      "kitchen": false
    },
    "outputs": {
      "btu": 1758.4264210333333,
      "base": 1758.4264210333333,
      "tons": 0.5,
      "watts": 1758.4264210333333
    },
    "text": "A 200 ft² room needs an air conditioner of about 6,000 BTU/h."
  },
  "examples": [
    {
      "given": {
        "area": 18.580608,
        "sun": "normal",
        "people": 2,
        "kitchen": false
      },
      "expect": {
        "btu": 1758.4264210333333,
        "tons": 0.5
      },
      "source": "ENERGY STAR sizing table: 150 to 250 ft² needs 6,000 BTU/h"
    },
    {
      "given": {
        "area": 37.161216,
        "sun": "sunny",
        "people": 4,
        "kitchen": false
      },
      "expect": {
        "base": 2930.7107017222224,
        "btu": 3575.467056101111
      },
      "source": "ENERGY STAR table: 400 to 450 ft² is 10,000 BTU/h; + 10% for a very sunny room = 11,000; + 600 × 2 extra people = 12,200 (hand calculation in content.mdx)"
    },
    {
      "given": {
        "area": 27.870912,
        "sun": "shaded",
        "people": 1,
        "kitchen": true
      },
      "expect": {
        "base": 2344.5685613777778,
        "btu": 3282.395985928889
      },
      "source": "ENERGY STAR table: 300 to 350 ft² is 8,000; − 10% for heavy shade = 7,200; + 4,000 for a kitchen = 11,200 (hand calculation in content.mdx)"
    },
    {
      "given": {
        "area": 232.25760000000002,
        "sun": "normal",
        "people": 2,
        "kitchen": false
      },
      "expect": {
        "btu": 9964.416385855555
      },
      "source": "ENERGY STAR table: 2,000 to 2,500 ft² needs 34,000 BTU/h (the last row includes 2,500)"
    },
    {
      "given": {
        "area": 30,
        "sun": "normal",
        "people": 2,
        "kitchen": false
      },
      "expect": {
        "btu": 2344.5685613777778
      },
      "source": "hand calculation in content.mdx: 30 ÷ 0.09290304 = 322.9 ft², in the 300 to 350 row: 8,000 BTU/h"
    }
  ],
  "sources": [
    "ENERGY STAR, Room Air Conditioners: sizing table by room area and the adjustments for shade, sun, occupants and kitchens. https://www.energystar.gov/products/room_air_conditioners",
    "NIST SP 811 (2008), Appendix B: 1 BTU (International Table) = 1,055.05585262 J; 1 ton of refrigeration = 12,000 BTU/h; 1 ft = 0.3048 m exactly."
  ],
  "related": [
    "electricity-cost",
    "square-footage"
  ],
  "changelog": []
}