{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"water-heater-energy"},"result":{"entity_type":"calculator","id":"water-heater-energy","calculator_id":"water-heater-energy","canonical_url":"https://tttkmbb.com/energy/water-heater-energy","name":"Water Heating Energy Calculator","title":"Water Heating Energy Calculator – kWh and Cost to Heat Water from Volume, Temperature Rise and Efficiency","category":"energy","category_name":"Home Energy & Electrical","tool_name":"calculate_water_heating_energy","featured_mcp_tool":false,"description":"Computes the energy needed to heat a volume of water by a given temperature rise (specific heat of water 4.186 kJ/(kg·K)) at a heater efficiency, the daily and annual energy and cost for repeated heating, and the heating time for a given heater power.","use_when":"You want the energy and cost of hot water for showers, a tank or a kettle, the annual cost of a water heater, or how long a heating element takes to heat a tank.","do_not_use_when":"You need standby losses of a storage tank or heat-pump water heater performance under varying conditions (enter its COP × 100 as the efficiency for a rough estimate), or non-water fluids (use specific-heat).","inputs":[{"name":"volume_liters","label":"Water volume","type":"number","unit":"L","required":true,"max":1000000,"exclusive_min":0,"description":"Volume of water heated per heating in litres (1 L ≈ 1 kg).","example":50},{"name":"temperature_rise_c","label":"Temperature rise","type":"number","unit":"°C","required":true,"max":100,"exclusive_min":0,"description":"Temperature increase in °C (or K), e.g. 40 to heat 15 °C mains water to 55 °C.","example":40},{"name":"efficiency_percent","label":"Heater efficiency","type":"number","unit":"%","required":false,"default":90,"min":10,"max":500,"description":"Share of the purchased energy that ends up in the water: 90–100 electric resistance, 60–95 gas, 200–400 for a heat-pump water heater (COP × 100).","example":90},{"name":"energy_price_per_kwh","label":"Energy price","type":"number","unit":"per kWh","required":false,"min":0,"max":100,"description":"Optional price per kWh of electricity or gas in your currency, for the daily and annual cost.","example":0.3},{"name":"heatings_per_day","label":"Heatings per day","type":"number","required":false,"default":1,"min":0,"max":100,"description":"How many times per day this volume is heated (e.g. number of showers).","example":1},{"name":"heater_power_kw","label":"Heater power","type":"number","unit":"kW","required":false,"max":1000,"exclusive_min":0,"description":"Optional heater input power in kW, to report the heating time of one volume.","example":2}],"outputs":[{"name":"energy_kwh","label":"Energy per heating","type":"number","unit":"kWh","decimals":3,"description":"4.186 × volume_liters × temperature_rise_c / 3600 / (efficiency_percent / 100)."},{"name":"energy_mj","label":"Energy per heating (MJ)","type":"number","unit":"MJ","decimals":3,"description":"energy_kwh × 3.6."},{"name":"heat_delivered_kwh","label":"Heat delivered to water","type":"number","unit":"kWh","decimals":3,"description":"Useful heat before efficiency losses: 4.186 × volume × ΔT / 3600."},{"name":"daily_energy_kwh","label":"Energy per day","type":"number","unit":"kWh","decimals":3,"description":"energy_kwh × heatings_per_day."},{"name":"annual_energy_kwh","label":"Energy per year","type":"number","unit":"kWh","decimals":1,"description":"daily_energy_kwh × 365."},{"name":"daily_cost","label":"Cost per day","type":"number","decimals":2,"description":"daily_energy_kwh × energy_price_per_kwh; only when a price is given."},{"name":"annual_cost","label":"Cost per year","type":"number","decimals":2,"description":"annual_energy_kwh × energy_price_per_kwh; only when a price is given."},{"name":"heating_time_hours","label":"Heating time","type":"number","unit":"h","decimals":2,"description":"energy_kwh / heater_power_kw; only when heater_power_kw is given."}],"input_schema":{"type":"object","properties":{"volume_liters":{"description":"Volume of water heated per heating in litres (1 L ≈ 1 kg). Unit: L.","type":"number","maximum":1000000,"exclusiveMinimum":0,"examples":[50],"x-unit":"L"},"temperature_rise_c":{"description":"Temperature increase in °C (or K), e.g. 40 to heat 15 °C mains water to 55 °C. Unit: °C.","type":"number","maximum":100,"exclusiveMinimum":0,"examples":[40],"x-unit":"°C"},"efficiency_percent":{"description":"Share of the purchased energy that ends up in the water: 90–100 electric resistance, 60–95 gas, 200–400 for a heat-pump water heater (COP × 100). Unit: %.","type":"number","minimum":10,"maximum":500,"default":90,"examples":[90],"x-unit":"%"},"energy_price_per_kwh":{"description":"Optional price per kWh of electricity or gas in your currency, for the daily and annual cost. Unit: per kWh.","type":"number","minimum":0,"maximum":100,"examples":[0.3],"x-unit":"per kWh"},"heatings_per_day":{"description":"How many times per day this volume is heated (e.g. number of showers).","type":"number","minimum":0,"maximum":100,"default":1,"examples":[1]},"heater_power_kw":{"description":"Optional heater input power in kW, to report the heating time of one volume. Unit: kW.","type":"number","maximum":1000,"exclusiveMinimum":0,"examples":[2],"x-unit":"kW"}},"additionalProperties":false,"required":["volume_liters","temperature_rise_c"]},"output_schema":{"type":"object","properties":{"energy_kwh":{"description":"4.186 × volume_liters × temperature_rise_c / 3600 / (efficiency_percent / 100). Unit: kWh.","type":"number","x-unit":"kWh"},"energy_mj":{"description":"energy_kwh × 3.6. Unit: MJ.","type":"number","x-unit":"MJ"},"heat_delivered_kwh":{"description":"Useful heat before efficiency losses: 4.186 × volume × ΔT / 3600. Unit: kWh.","type":"number","x-unit":"kWh"},"daily_energy_kwh":{"description":"energy_kwh × heatings_per_day. Unit: kWh.","type":"number","x-unit":"kWh"},"annual_energy_kwh":{"description":"daily_energy_kwh × 365. Unit: kWh.","type":"number","x-unit":"kWh"},"daily_cost":{"description":"daily_energy_kwh × energy_price_per_kwh; only when a price is given.","type":"number"},"annual_cost":{"description":"annual_energy_kwh × energy_price_per_kwh; only when a price is given.","type":"number"},"heating_time_hours":{"description":"energy_kwh / heater_power_kw; only when heater_power_kw is given. Unit: h.","type":"number","x-unit":"h"}}},"formula":"heat_delivered_kwh = 4.186 × volume_liters × temperature_rise_c / 3600; energy_kwh = heat_delivered_kwh / (efficiency_percent / 100); energy_mj = energy_kwh × 3.6; daily_energy_kwh = energy_kwh × heatings_per_day; annual_energy_kwh = daily_energy_kwh × 365; cost = energy × energy_price_per_kwh; heating_time_hours = energy_kwh / heater_power_kw","method":"Q = m·c·ΔT with c = 4.186 kJ/(kg·K) and 1 kg per litre (density variation with temperature ignored, < 2 %). The efficiency converts delivered heat into purchased energy; storage standby losses are not included.","sources":[{"name":"Wikipedia – Specific heat capacity","url":"https://en.wikipedia.org/wiki/Specific_heat_capacity","type":"reference","retrieved_at":"2026-09-24"},{"name":"U.S. DOE Energy Saver – Sizing a New Water Heater","url":"https://www.energy.gov/energysaver/sizing-new-water-heater","type":"government","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":"50 L by 40 °C at 100 % efficiency","inputs":{"volume_liters":50,"temperature_rise_c":40,"efficiency_percent":100},"expected":{"energy_kwh":2.326,"energy_mj":8.372,"heat_delivered_kwh":2.326,"annual_energy_kwh":848.8},"url":"https://tttkmbb.com/api/v1/calculate/water-heater-energy?volume_liters=50&temperature_rise_c=40&efficiency_percent=100"},{"name":"50 L by 40 °C at 90 %, twice a day, 0.30 per kWh, 2 kW element","inputs":{"volume_liters":50,"temperature_rise_c":40,"efficiency_percent":90,"energy_price_per_kwh":0.3,"heatings_per_day":2,"heater_power_kw":2},"expected":{"energy_kwh":2.584,"daily_energy_kwh":5.168,"annual_energy_kwh":1886.3,"daily_cost":1.55,"annual_cost":565.89,"heating_time_hours":1.29},"url":"https://tttkmbb.com/api/v1/calculate/water-heater-energy?volume_liters=50&temperature_rise_c=40&efficiency_percent=90&energy_price_per_kwh=0.3&heatings_per_day=2&heater_power_kw=2"}],"faq":[{"q":"How much energy does a shower use?","a":"A 10-minute shower at 9 L/min uses 90 L; heating it from 15 °C to 40 °C (ΔT 25 K) needs 2.6 kWh of heat, about 2.9 kWh of electricity at 90 % efficiency."},{"q":"How do I model a heat-pump water heater?","a":"Enter its coefficient of performance times 100 as efficiency_percent (COP 3 → 300 %); the calculator then divides the heat by 3."},{"q":"Why does a gas heater cost less despite lower efficiency?","a":"Efficiency converts heat to purchased energy; cost also depends on the price per kWh, and gas is usually cheaper per kWh than electricity. Enter the gas price per kWh (price per m³ ÷ ≈ 10.5 kWh/m³)."}],"tags":["water heating energy","kwh to heat water","water heater cost","shower energy cost","boiler energy","specific heat water"],"related":[{"calculator_id":"specific-heat","reason":"Heat energy for other substances and units."},{"calculator_id":"electricity-cost","reason":"Cost of the kWh at several tariffs."},{"calculator_id":"solar-payback","reason":"Solar electricity that could supply the water heater."}],"links":{"html":"https://tttkmbb.com/energy/water-heater-energy","markdown":"https://tttkmbb.com/energy/water-heater-energy.md","json":"https://tttkmbb.com/energy/water-heater-energy.json","api":"https://tttkmbb.com/api/v1/calculate/water-heater-energy","schema":"https://tttkmbb.com/api/v1/calculators/water-heater-energy","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-24T03:51:43Z","next_actions":[{"tool":"run_calculator","calculator_id":"water-heater-energy","reason":"Run Water Heating Energy Calculator with the inputs above."}],"links":{"markdown":"https://tttkmbb.com/energy/water-heater-energy.md"}}