{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"hvac-btu-sizing"},"result":{"entity_type":"calculator","id":"hvac-btu-sizing","calculator_id":"hvac-btu-sizing","canonical_url":"https://tttkmbb.com/energy/hvac-btu-sizing","name":"HVAC BTU Sizing Calculator","title":"HVAC BTU Sizing Calculator – Air Conditioner and Heater Capacity from Room Area, Climate, Sun and Occupancy","category":"energy","category_name":"Home Energy & Electrical","tool_name":"estimate_hvac_btu_sizing","featured_mcp_tool":false,"description":"Estimates the cooling capacity (BTU/h, tons, kW) and heating output a room needs from floor area, ceiling height, climate, sun exposure, insulation, occupants and kitchen heat, using the 20 BTU/h per ft² rule of thumb with the ENERGY STAR room air conditioner adjustments.","use_when":"You need a quick size for a window, portable or split air conditioner or a room heater before shopping, or want to sanity-check a quoted unit size.","do_not_use_when":"You need a code-grade load calculation for a whole house (ACCA Manual J / ASHRAE methods account for windows, orientation and infiltration), or the heat flow through one wall (use heat-loss).","inputs":[{"name":"floor_area","label":"Floor area","type":"number","required":true,"max":100000,"exclusive_min":0,"description":"Floor area of the room or zone, in the unit given by area_unit.","example":400},{"name":"area_unit","label":"Area unit","type":"enum","required":false,"default":"ft2","values":[{"value":"ft2","label":"Square feet","aliases":["sqft","ft²","square_feet"]},{"value":"m2","label":"Square metres","aliases":["sqm","m²","square_meters"]}],"description":"Unit of floor_area (1 m² = 10.76391 ft²).","example":"ft2"},{"name":"ceiling_height_ft","label":"Ceiling height","type":"number","unit":"ft","required":false,"default":8,"min":6,"max":30,"description":"Ceiling height in feet; the base rates assume 8 ft and scale with ceiling_height_ft / 8.","example":8},{"name":"climate","label":"Climate","type":"enum","required":false,"default":"moderate","values":[{"value":"cool","label":"Cool (cooling ×0.9, heating 60 BTU/h per ft²)"},{"value":"moderate","label":"Moderate (cooling ×1.0, heating 45 BTU/h per ft²)","aliases":["temperate"]},{"value":"warm","label":"Warm (cooling ×1.1, heating 35 BTU/h per ft²)"},{"value":"hot","label":"Hot (cooling ×1.2, heating 30 BTU/h per ft²)"}],"description":"Local climate: multiplies the cooling load (0.9 / 1.0 / 1.1 / 1.2) and sets the heating rate (60 / 45 / 35 / 30 BTU/h per ft²).","example":"moderate"},{"name":"sun_exposure","label":"Sun exposure","type":"enum","required":false,"default":"average","values":[{"value":"shaded","label":"Heavily shaded (×0.9)","aliases":["shade"]},{"value":"average","label":"Average (×1.0)","aliases":["normal"]},{"value":"sunny","label":"Very sunny (×1.1)","aliases":["sun"]}],"description":"Sunlight on the room: shaded −10 %, sunny +10 % cooling load (ENERGY STAR).","example":"average"},{"name":"occupants","label":"Occupants","type":"integer","required":false,"default":2,"min":0,"max":500,"description":"People regularly in the room; each person above 2 adds 600 BTU/h of cooling load.","example":2},{"name":"kitchen","label":"Kitchen","type":"boolean","required":false,"default":false,"description":"true when the room is a kitchen (adds 4,000 BTU/h of cooling load for cooking appliances).","example":false},{"name":"insulation","label":"Insulation","type":"enum","required":false,"default":"average","values":[{"value":"poor","label":"Poor (×1.15)","aliases":["bad","old"]},{"value":"average","label":"Average (×1.0)"},{"value":"good","label":"Good (×0.9)","aliases":["well_insulated"]}],"description":"Quality of walls, roof and windows; multiplies both cooling and heating loads.","example":"average"}],"outputs":[{"name":"cooling_btu_per_hour","label":"Cooling capacity","type":"number","unit":"BTU/h","decimals":0,"description":"Estimated cooling load: 20 BTU/h per ft² adjusted for ceiling height, climate, sun, insulation, occupants and kitchen."},{"name":"cooling_tons","label":"Cooling capacity (tons)","type":"number","unit":"ton","decimals":2,"description":"Cooling load in tons of refrigeration (1 ton = 12,000 BTU/h)."},{"name":"cooling_kw","label":"Cooling capacity (kW)","type":"number","unit":"kW","decimals":2,"description":"Cooling load in kilowatts (1 BTU/h = 0.29307 W)."},{"name":"heating_btu_per_hour","label":"Heating output","type":"number","unit":"BTU/h","decimals":0,"description":"Estimated heating load: climate heating rate × area, adjusted for ceiling height and insulation."},{"name":"heating_kw","label":"Heating output (kW)","type":"number","unit":"kW","decimals":2,"description":"Heating load in kilowatts."},{"name":"floor_area_ft2","label":"Floor area","type":"number","unit":"ft²","decimals":1,"description":"Floor area used, in square feet."},{"name":"recommended_unit_size_text","label":"Recommended unit size","type":"string","decimals":4,"description":"Cooling capacity rounded up to the next 1,000 BTU/h (window units are sold in such steps), heating rounded up likewise, with the assumptions stated."}],"input_schema":{"type":"object","properties":{"floor_area":{"description":"Floor area of the room or zone, in the unit given by area_unit.","type":"number","maximum":100000,"exclusiveMinimum":0,"examples":[400]},"area_unit":{"description":"Unit of floor_area (1 m² = 10.76391 ft²).","type":"string","enum":["ft2","m2"],"default":"ft2","examples":["ft2"]},"ceiling_height_ft":{"description":"Ceiling height in feet; the base rates assume 8 ft and scale with ceiling_height_ft / 8. Unit: ft.","type":"number","minimum":6,"maximum":30,"default":8,"examples":[8],"x-unit":"ft"},"climate":{"description":"Local climate: multiplies the cooling load (0.9 / 1.0 / 1.1 / 1.2) and sets the heating rate (60 / 45 / 35 / 30 BTU/h per ft²).","type":"string","enum":["cool","moderate","warm","hot"],"default":"moderate","examples":["moderate"]},"sun_exposure":{"description":"Sunlight on the room: shaded −10 %, sunny +10 % cooling load (ENERGY STAR).","type":"string","enum":["shaded","average","sunny"],"default":"average","examples":["average"]},"occupants":{"description":"People regularly in the room; each person above 2 adds 600 BTU/h of cooling load.","type":"integer","minimum":0,"maximum":500,"default":2,"examples":[2]},"kitchen":{"description":"true when the room is a kitchen (adds 4,000 BTU/h of cooling load for cooking appliances).","type":"boolean","default":false,"examples":[false]},"insulation":{"description":"Quality of walls, roof and windows; multiplies both cooling and heating loads.","type":"string","enum":["poor","average","good"],"default":"average","examples":["average"]}},"additionalProperties":false,"required":["floor_area"]},"output_schema":{"type":"object","properties":{"cooling_btu_per_hour":{"description":"Estimated cooling load: 20 BTU/h per ft² adjusted for ceiling height, climate, sun, insulation, occupants and kitchen. Unit: BTU/h.","type":"number","x-unit":"BTU/h"},"cooling_tons":{"description":"Cooling load in tons of refrigeration (1 ton = 12,000 BTU/h). Unit: ton.","type":"number","x-unit":"ton"},"cooling_kw":{"description":"Cooling load in kilowatts (1 BTU/h = 0.29307 W). Unit: kW.","type":"number","x-unit":"kW"},"heating_btu_per_hour":{"description":"Estimated heating load: climate heating rate × area, adjusted for ceiling height and insulation. Unit: BTU/h.","type":"number","x-unit":"BTU/h"},"heating_kw":{"description":"Heating load in kilowatts. Unit: kW.","type":"number","x-unit":"kW"},"floor_area_ft2":{"description":"Floor area used, in square feet. Unit: ft².","type":"number","x-unit":"ft²"},"recommended_unit_size_text":{"description":"Cooling capacity rounded up to the next 1,000 BTU/h (window units are sold in such steps), heating rounded up likewise, with the assumptions stated.","type":"string"}}},"formula":"area_ft2 = floor_area (× 10.76391 if m²); cooling_btu_per_hour = area_ft2 × 20 × (ceiling_height_ft / 8) × climate_factor × sun_factor × insulation_factor + 600 × max(0, occupants − 2) + (kitchen ? 4000 : 0); heating_btu_per_hour = area_ft2 × heating_rate(climate) × (ceiling_height_ft / 8) × insulation_factor; cooling_tons = BTU/h / 12000; kW = BTU/h × 0.29307 / 1000","method":"Rule-of-thumb sizing (20 BTU/h per ft² base cooling load) with the ENERGY STAR adjustments: heavily shaded −10 %, very sunny +10 %, +600 BTU/h per person above two, +4,000 BTU/h for kitchens; heating uses 30–60 BTU/h per ft² depending on climate. Oversized air conditioners short-cycle and dehumidify poorly, so do not round up beyond the next available size.","sources":[{"name":"ENERGY STAR – Room Air Conditioners (sizing chart and adjustments)","url":"https://www.energystar.gov/products/room_air_conditioners","type":"government","retrieved_at":"2026-09-24"},{"name":"ASHRAE Handbook – Fundamentals","url":"https://www.ashrae.org/technical-resources/ashrae-handbook","type":"standard","retrieved_at":"2026-09-24"}],"freshness":{"type":"static","max_age_seconds":null,"note":"Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output."},"examples":[{"name":"400 ft² room, moderate climate, defaults","inputs":{"floor_area":400,"area_unit":"ft2","ceiling_height_ft":8,"climate":"moderate","sun_exposure":"average","occupants":2,"kitchen":false,"insulation":"average"},"expected":{"cooling_btu_per_hour":8000,"cooling_tons":0.67,"cooling_kw":2.34,"heating_btu_per_hour":18000,"heating_kw":5.28},"url":"https://tttkmbb.com/api/v1/calculate/hvac-btu-sizing?floor_area=400&area_unit=ft2&ceiling_height_ft=8&climate=moderate&sun_exposure=average&occupants=2&kitchen=false&insulation=average"},{"name":"30 m² sunny kitchen, hot climate, 9 ft ceiling, 4 people, poor insulation","inputs":{"floor_area":30,"area_unit":"m2","ceiling_height_ft":9,"climate":"hot","sun_exposure":"sunny","occupants":4,"kitchen":true,"insulation":"poor"},"expected":{"floor_area_ft2":322.9,"cooling_btu_per_hour":16229,"cooling_tons":1.35,"cooling_kw":4.76,"heating_btu_per_hour":12533},"url":"https://tttkmbb.com/api/v1/calculate/hvac-btu-sizing?floor_area=30&area_unit=m2&ceiling_height_ft=9&climate=hot&sun_exposure=sunny&occupants=4&kitchen=true&insulation=poor"}],"faq":[{"q":"Why does ENERGY STAR's chart give a different number for my area?","a":"The chart lists capacities in 1,000 BTU/h steps for area bands (e.g. 350–400 ft² → 9,000 BTU/h) and averages to roughly 20–25 BTU/h per ft²; this calculator uses the continuous 20 BTU/h per ft² rule with the same shade, sun, occupant and kitchen adjustments."},{"q":"Is the heating figure the furnace or heat-pump size?","a":"It is the required heat output at the design temperature. A heat pump's rated heating capacity falls at low outdoor temperatures, so compare with its capacity at your design temperature, not the nameplate."},{"q":"What are BTU/h, tons and kW?","a":"All three are rates of heat flow: 12,000 BTU/h = 1 ton of refrigeration = 3.517 kW. Air conditioner electrical input is lower than the cooling output (divide by the EER or COP)."}],"tags":["btu calculator","air conditioner size","hvac sizing","cooling capacity","heater size","tons of cooling"],"related":[{"calculator_id":"heat-loss","reason":"Heat flow through one wall, roof or window from its U-value."},{"calculator_id":"air-changes-per-hour","reason":"Ventilation rate of the same room."},{"calculator_id":"electricity-cost","reason":"Running cost of the air conditioner from its wattage and hours."}],"links":{"html":"https://tttkmbb.com/energy/hvac-btu-sizing","markdown":"https://tttkmbb.com/energy/hvac-btu-sizing.md","json":"https://tttkmbb.com/energy/hvac-btu-sizing.json","api":"https://tttkmbb.com/api/v1/calculate/hvac-btu-sizing","schema":"https://tttkmbb.com/api/v1/calculators/hvac-btu-sizing","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-24T03:48:18Z"}