{
  "id": "v20-us-heat-loss",
  "version": "20.16.0",
  "name": "Room Heat Loss Calculator — United States",
  "shortName": "Room Heat Loss",
  "description": "Estimate steady-state room heat loss from entered fabric properties, air exchange and a local outdoor design temperature. USD planning view; stated limitations apply.",
  "category": "Home & Construction",
  "categorySlug": "home-construction",
  "keywords": [
    "heat-loss",
    "us",
    "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-us-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": "/us/heat-loss/",
    "definition": "/us/heat-loss/definition.json",
    "schema": "/us/heat-loss/schema.json",
    "llms": "/us/heat-loss/llms.txt",
    "legacyDefinition": "/us/heat-loss/definition.json"
  },
  "queryExample": "https://askcalculators.com/us/heat-loss/?unitSystem=imperial&wallArea=538.195520835486&wallU=0.05283305514296545&roofArea=430.55641666838886&roofU=0.035222036761976966&windowArea=86.11128333367778&windowU=0.24655425733383876&floorArea=430.55641666838886&floorU=0.04402754595247121&volume=3531.466672148859&airChanges=0.5&insideTemp=68&outsideTemp=23",
  "queryParameters": {
    "unitSystem": {
      "label": "Measurement system",
      "type": "select",
      "required": false,
      "default": "imperial"
    },
    "wallArea": {
      "label": "Exposed opaque wall area",
      "type": "number",
      "required": true,
      "default": 538.195520835486
    },
    "wallU": {
      "label": "Wall U-value",
      "type": "number",
      "required": true,
      "default": 0.05283305514296545
    },
    "roofArea": {
      "label": "Exposed roof area",
      "type": "number",
      "required": true,
      "default": 430.55641666838886
    },
    "roofU": {
      "label": "Roof U-value",
      "type": "number",
      "required": true,
      "default": 0.035222036761976966
    },
    "windowArea": {
      "label": "Window and external door area",
      "type": "number",
      "required": true,
      "default": 86.11128333367778
    },
    "windowU": {
      "label": "Window/door U-value",
      "type": "number",
      "required": true,
      "default": 0.24655425733383876
    },
    "floorArea": {
      "label": "Exposed floor area",
      "type": "number",
      "required": true,
      "default": 430.55641666838886
    },
    "floorU": {
      "label": "Floor U-value",
      "type": "number",
      "required": true,
      "default": 0.04402754595247121
    },
    "volume": {
      "label": "Heated internal volume",
      "type": "number",
      "required": true,
      "default": 3531.466672148859
    },
    "airChanges": {
      "label": "Air changes per hour",
      "type": "number",
      "required": true,
      "default": 0.5
    },
    "insideTemp": {
      "label": "Indoor design temperature",
      "type": "number",
      "required": true,
      "default": 68
    },
    "outsideTemp": {
      "label": "Outdoor design temperature",
      "type": "number",
      "required": true,
      "default": 23
    }
  },
  "inputs": [
    {
      "id": "unitSystem",
      "label": "Measurement system",
      "type": "select",
      "defaultValue": "imperial",
      "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": 538.195520835486,
      "required": true,
      "min": 0,
      "max": 10763910416709.72,
      "suffix": "ft²",
      "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": 0.05283305514296545,
      "required": true,
      "min": 0.0017611018380988483,
      "max": 1.7611018380988483,
      "suffix": "BTU/(h·ft²·°F)",
      "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": 430.55641666838886,
      "required": true,
      "min": 0,
      "max": 10763910416709.72,
      "suffix": "ft²",
      "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": 0.035222036761976966,
      "required": true,
      "min": 0.0017611018380988483,
      "max": 1.7611018380988483,
      "suffix": "BTU/(h·ft²·°F)",
      "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": 86.11128333367778,
      "required": true,
      "min": 0,
      "max": 10763910416709.72,
      "suffix": "ft²",
      "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": 0.24655425733383876,
      "required": true,
      "min": 0.0017611018380988483,
      "max": 3.5222036761976967,
      "suffix": "BTU/(h·ft²·°F)",
      "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": 430.55641666838886,
      "required": true,
      "min": 0,
      "max": 10763910416709.72,
      "suffix": "ft²",
      "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": 0.04402754595247121,
      "required": true,
      "min": 0.0017611018380988483,
      "max": 1.7611018380988483,
      "suffix": "BTU/(h·ft²·°F)",
      "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": 3531.466672148859,
      "required": true,
      "min": 0,
      "max": 35314666721488.586,
      "suffix": "ft³",
      "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": 68,
      "required": true,
      "min": 14,
      "max": 104,
      "suffix": "°F",
      "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": 23,
      "required": true,
      "min": -112,
      "max": 104,
      "suffix": "°F",
      "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": "imperial",
        "wallArea": 538.195520835486,
        "wallU": 0.05283305514296545,
        "roofArea": 430.55641666838886,
        "roofU": 0.035222036761976966,
        "windowArea": 86.11128333367778,
        "windowU": 0.24655425733383876,
        "floorArea": 430.55641666838886,
        "floorU": 0.04402754595247121,
        "volume": 3531.466672148859,
        "airChanges": 0.5,
        "insideTemp": 68,
        "outsideTemp": 23
      }
    }
  ],
  "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": "us",
  "countries": [
    "us",
    "ca",
    "uk",
    "ie"
  ]
}