{
  "id": "v20-uk-heat-loss",
  "version": "20.16.0",
  "name": "Room Heat Loss Calculator — United Kingdom",
  "shortName": "Room Heat Loss",
  "description": "Estimate steady-state room heat loss from entered fabric properties, air exchange and a local outdoor design temperature. GBP planning view; stated limitations apply.",
  "category": "Home & Construction",
  "categorySlug": "home-construction",
  "keywords": [
    "heat-loss",
    "uk",
    "energy-conservation",
    "pvwatts",
    "energy-saver"
  ],
  "status": "live",
  "workStatus": "pending",
  "reviewStatus": "pending",
  "migrationStatus": "new",
  "engine": "native",
  "creator": null,
  "reviewer": null,
  "quality": {
    "availability": "live",
    "technicalReviewRecord": "/reviews/v20-uk-heat-loss.json",
    "qualifiedReview": "pending",
    "qualifiedReviewer": null,
    "qualifiedReviewDate": null,
    "formulaVersion": "20.16.0",
    "referenceCoverage": "references-listed",
    "releaseTestScope": "Catalog and regression checks are not a professional formula audit; consult release evidence.",
    "historicalMetadataDate": "",
    "historicalMetadataNotice": "The imported date is not evidence of a completed human review."
  },
  "notice": "Illustrative defaults are not local quotes or verified legal rules. Dated reference components and user-entered assumptions are explicitly distinguished. Professional review is pending.",
  "urls": {
    "page": "/uk/heat-loss/",
    "definition": "/uk/heat-loss/definition.json",
    "schema": "/uk/heat-loss/schema.json",
    "llms": "/uk/heat-loss/llms.txt",
    "legacyDefinition": "/uk/heat-loss/definition.json"
  },
  "queryExample": "https://askcalculators.com/uk/heat-loss/?unitSystem=metric&wallArea=50&wallU=0.3&roofArea=40&roofU=0.2&windowArea=8&windowU=1.4&floorArea=40&floorU=0.25&volume=100&airChanges=0.5&insideTemp=20&outsideTemp=-5",
  "queryParameters": {
    "unitSystem": {
      "label": "Measurement system",
      "type": "select",
      "required": false,
      "default": "metric"
    },
    "wallArea": {
      "label": "Exposed opaque wall area",
      "type": "number",
      "required": true,
      "default": 50
    },
    "wallU": {
      "label": "Wall U-value",
      "type": "number",
      "required": true,
      "default": 0.3
    },
    "roofArea": {
      "label": "Exposed roof area",
      "type": "number",
      "required": true,
      "default": 40
    },
    "roofU": {
      "label": "Roof U-value",
      "type": "number",
      "required": true,
      "default": 0.2
    },
    "windowArea": {
      "label": "Window and external door area",
      "type": "number",
      "required": true,
      "default": 8
    },
    "windowU": {
      "label": "Window/door U-value",
      "type": "number",
      "required": true,
      "default": 1.4
    },
    "floorArea": {
      "label": "Exposed floor area",
      "type": "number",
      "required": true,
      "default": 40
    },
    "floorU": {
      "label": "Floor U-value",
      "type": "number",
      "required": true,
      "default": 0.25
    },
    "volume": {
      "label": "Heated internal volume",
      "type": "number",
      "required": true,
      "default": 100
    },
    "airChanges": {
      "label": "Air changes per hour",
      "type": "number",
      "required": true,
      "default": 0.5
    },
    "insideTemp": {
      "label": "Indoor design temperature",
      "type": "number",
      "required": true,
      "default": 20
    },
    "outsideTemp": {
      "label": "Outdoor design temperature",
      "type": "number",
      "required": true,
      "default": -5
    }
  },
  "inputs": [
    {
      "id": "unitSystem",
      "label": "Measurement system",
      "type": "select",
      "defaultValue": "metric",
      "options": [
        {
          "value": "imperial",
          "label": "Imperial (US gallons / short tons where relevant)"
        },
        {
          "value": "metric",
          "label": "Metric"
        }
      ]
    },
    {
      "id": "wallArea",
      "label": "Exposed opaque wall area",
      "type": "number",
      "defaultValue": 50,
      "required": true,
      "min": 0,
      "max": 1000000000000,
      "suffix": "m²",
      "unitConversion": {
        "factor": 0.09290304,
        "offset": 0,
        "inverse": false,
        "metric": "m²",
        "imperial": "ft²",
        "canonicalMin": 0,
        "canonicalMax": 1000000000000
      },
      "help": "Illustrative starting value; replace with your own evidence."
    },
    {
      "id": "wallU",
      "label": "Wall U-value",
      "type": "number",
      "defaultValue": 0.3,
      "required": true,
      "min": 0.01,
      "max": 10,
      "suffix": "W/(m²·K)",
      "unitConversion": {
        "factor": 5.678263337,
        "offset": 0,
        "inverse": false,
        "metric": "W/(m²·K)",
        "imperial": "BTU/(h·ft²·°F)",
        "canonicalMin": 0.01,
        "canonicalMax": 10
      },
      "help": "Illustrative starting value; replace with your own evidence."
    },
    {
      "id": "roofArea",
      "label": "Exposed roof area",
      "type": "number",
      "defaultValue": 40,
      "required": true,
      "min": 0,
      "max": 1000000000000,
      "suffix": "m²",
      "unitConversion": {
        "factor": 0.09290304,
        "offset": 0,
        "inverse": false,
        "metric": "m²",
        "imperial": "ft²",
        "canonicalMin": 0,
        "canonicalMax": 1000000000000
      },
      "help": "Illustrative starting value; replace with your own evidence."
    },
    {
      "id": "roofU",
      "label": "Roof U-value",
      "type": "number",
      "defaultValue": 0.2,
      "required": true,
      "min": 0.01,
      "max": 10,
      "suffix": "W/(m²·K)",
      "unitConversion": {
        "factor": 5.678263337,
        "offset": 0,
        "inverse": false,
        "metric": "W/(m²·K)",
        "imperial": "BTU/(h·ft²·°F)",
        "canonicalMin": 0.01,
        "canonicalMax": 10
      },
      "help": "Illustrative starting value; replace with your own evidence."
    },
    {
      "id": "windowArea",
      "label": "Window and external door area",
      "type": "number",
      "defaultValue": 8,
      "required": true,
      "min": 0,
      "max": 1000000000000,
      "suffix": "m²",
      "unitConversion": {
        "factor": 0.09290304,
        "offset": 0,
        "inverse": false,
        "metric": "m²",
        "imperial": "ft²",
        "canonicalMin": 0,
        "canonicalMax": 1000000000000
      },
      "help": "Illustrative starting value; replace with your own evidence."
    },
    {
      "id": "windowU",
      "label": "Window/door U-value",
      "type": "number",
      "defaultValue": 1.4,
      "required": true,
      "min": 0.01,
      "max": 20,
      "suffix": "W/(m²·K)",
      "unitConversion": {
        "factor": 5.678263337,
        "offset": 0,
        "inverse": false,
        "metric": "W/(m²·K)",
        "imperial": "BTU/(h·ft²·°F)",
        "canonicalMin": 0.01,
        "canonicalMax": 20
      },
      "help": "Illustrative starting value; replace with your own evidence."
    },
    {
      "id": "floorArea",
      "label": "Exposed floor area",
      "type": "number",
      "defaultValue": 40,
      "required": true,
      "min": 0,
      "max": 1000000000000,
      "suffix": "m²",
      "unitConversion": {
        "factor": 0.09290304,
        "offset": 0,
        "inverse": false,
        "metric": "m²",
        "imperial": "ft²",
        "canonicalMin": 0,
        "canonicalMax": 1000000000000
      },
      "help": "Illustrative starting value; replace with your own evidence."
    },
    {
      "id": "floorU",
      "label": "Floor U-value",
      "type": "number",
      "defaultValue": 0.25,
      "required": true,
      "min": 0.01,
      "max": 10,
      "suffix": "W/(m²·K)",
      "unitConversion": {
        "factor": 5.678263337,
        "offset": 0,
        "inverse": false,
        "metric": "W/(m²·K)",
        "imperial": "BTU/(h·ft²·°F)",
        "canonicalMin": 0.01,
        "canonicalMax": 10
      },
      "help": "Illustrative starting value; replace with your own evidence."
    },
    {
      "id": "volume",
      "label": "Heated internal volume",
      "type": "number",
      "defaultValue": 100,
      "required": true,
      "min": 0,
      "max": 1000000000000,
      "suffix": "m³",
      "unitConversion": {
        "factor": 0.028316846592,
        "offset": 0,
        "inverse": false,
        "metric": "m³",
        "imperial": "ft³",
        "canonicalMin": 0,
        "canonicalMax": 1000000000000
      },
      "help": "Illustrative starting value; replace with your own evidence."
    },
    {
      "id": "airChanges",
      "label": "Air changes per hour",
      "type": "number",
      "defaultValue": 0.5,
      "required": true,
      "min": 0,
      "max": 20,
      "step": 0.01,
      "help": "Illustrative starting value; replace with your own evidence."
    },
    {
      "id": "insideTemp",
      "label": "Indoor design temperature",
      "type": "number",
      "defaultValue": 20,
      "required": true,
      "min": -10,
      "max": 40,
      "suffix": "°C",
      "unitConversion": {
        "factor": 0.5555555555555556,
        "offset": -17.77777777777778,
        "inverse": false,
        "metric": "°C",
        "imperial": "°F",
        "canonicalMin": -10,
        "canonicalMax": 40
      },
      "help": "Illustrative starting value; replace with your own evidence."
    },
    {
      "id": "outsideTemp",
      "label": "Outdoor design temperature",
      "type": "number",
      "defaultValue": -5,
      "required": true,
      "min": -80,
      "max": 40,
      "suffix": "°C",
      "unitConversion": {
        "factor": 0.5555555555555556,
        "offset": -17.77777777777778,
        "inverse": false,
        "metric": "°C",
        "imperial": "°F",
        "canonicalMin": -80,
        "canonicalMax": 40
      },
      "help": "Illustrative starting value; replace with your own evidence."
    }
  ],
  "outputs": [
    {
      "id": "fabricLoss",
      "label": "Fabric design heat loss",
      "format": "number",
      "digits": 2,
      "unit": "thermalPower"
    },
    {
      "id": "ventilationLoss",
      "label": "Ventilation design heat loss",
      "format": "number",
      "digits": 2,
      "unit": "thermalPower"
    },
    {
      "id": "totalLoss",
      "label": "Total screening heat loss",
      "format": "number",
      "digits": 2,
      "unit": "thermalPower",
      "primary": true
    }
  ],
  "formula": {
    "expression": "heat loss, W = Σ(area × U-value × temperature difference) + 0.33 × air changes × room volume × temperature difference.",
    "note": "Inputs are converted to canonical units before evaluating this stated formula."
  },
  "examples": [
    {
      "label": "Illustrative defaults; required verification checks remain unconfirmed",
      "inputs": {
        "unitSystem": "metric",
        "wallArea": 50,
        "wallU": 0.3,
        "roofArea": 40,
        "roofU": 0.2,
        "windowArea": 8,
        "windowU": 1.4,
        "floorArea": 40,
        "floorU": 0.25,
        "volume": 100,
        "airChanges": 0.5,
        "insideTemp": 20,
        "outsideTemp": -5
      }
    }
  ],
  "sources": [
    {
      "label": "DOE energy-use arithmetic",
      "url": "https://www.energy.gov/energysaver/save-electricity-and-fuel/appliances-and-electronics/estimating-appliance-and-home"
    },
    {
      "label": "PVWatts: site-specific solar estimation",
      "url": "https://pvwatts.nlr.gov/"
    },
    {
      "label": "DOE insulation overview",
      "url": "https://www.energy.gov/energysaver/weatherize/insulation"
    }
  ],
  "publicSlug": "heat-loss",
  "namespace": "uk",
  "countries": [
    "us",
    "ca",
    "uk",
    "ie"
  ]
}