# Water heater cost comparison - Human page: https://happytails.ai/en/calculators/water-heater-cost-comparison/ - Markdown: https://happytails.ai/en/calculators/water-heater-cost-comparison.md - Structured JSON: https://happytails.ai/agents/en/calculators/water-heater-cost-comparison/index.json - Visibility: public ## Tool capabilities | Property | Value | | --- | --- | | Tool ID | `water-heater-cost-comparison` | | Category | calculators | | Implementation | Registered implementation. Registration alone is not a production-quality guarantee. | | Browser execution | Use the visible action or interactive controls. | | Browser processing | Browser; see tool notes for network behavior. | | HTTP API | Not callable through HTTP. | | Browser-agent interface | run_current_tool | ### Implementation notes Calculated on your device for up to 30 heater options and 100,000 characters. Enter efficiency or COP, input-energy standby loss and tariff for each option. ### Inputs and settings Text input: Heater options. Example or placeholder shown in the interface (not a validated fixture): ```text Stored electric,Storage,electricity,0.8,1,0.2 ``` One option per line: name, type, fuel, efficiency or COP, standby input kWh/day and price per input kWh. Up to 100,000 characters. Review the settings before running. | Setting | Meaning | Control type | Default | Constraints | | --- | --- | --- | --- | --- | | `volumeUnit` | Daily hot-water volume unit | select | "L" | Allowed: L, US gal, Imp gal | | `volume` | Daily hot-water volume | number | 100 | min=0 step=any | | `temperatureUnit` | Temperature rise unit | select | "K" | Allowed: K, °C, °F | | `rise` | Water temperature rise | number | 40 | min=0 step=any | | `days` | Days per year | number | 365 | min=0 max=366 step=1 | ### Browser-agent workflow 1. Open the human page in a browser that supports WebMCP. 2. Discover the interface exposed by that page; use its actual schema. 3. Select files on the page first when the tool requires files. 4. Call `run_current_tool` with valid input and settings. 5. Inspect the returned result or error and the displayed output. Retrieve files from the displayed download links. Calls do not automatically copy or download results. Browser permissions still apply. Interface availability alone is not proof of successful execution. ### Planning specification Up to 30 uniquely named options and 100,000 characters. Daily volume 0 to 10 million L in L, US gal or Imp gal; temperature rise 0 to 100 K in K, °C or °F; 1 to 366 whole days. Storage/instantaneous efficiency above 0 to 1, heat-pump COP above 0 to 20, standby 0 to 100,000 input kWh/day and prices 0 to 100,000 per input kWh. Calculated on your device. Downloads: JSON report, results CSV and ranked option CSV. This describes intended requirements. Use the implementation notes, interface schema and observed output to determine current support. ### Complete machine-readable capability record ```json { "id": "water-heater-cost-comparison", "category": "calculators", "built": true, "requirements": "Up to 30 uniquely named options and 100,000 characters. Daily volume 0 to 10 million L in L, US gal or Imp gal; temperature rise 0 to 100 K in K, °C or °F; 1 to 366 whole days. Storage/instantaneous efficiency above 0 to 1, heat-pump COP above 0 to 20, standby 0 to 100,000 input kWh/day and prices 0 to 100,000 per input kWh. Calculated on your device. Downloads: JSON report, results CSV and ranked option CSV.", "implementation": { "fields": [ { "key": "volumeUnit", "label": "Daily hot-water volume unit", "value": "L", "type": "select", "values": [ "L", "US gal", "Imp gal" ] }, { "key": "volume", "label": "Daily hot-water volume", "value": 100, "type": "number", "min": 0, "step": "any" }, { "key": "temperatureUnit", "label": "Temperature rise unit", "value": "K", "type": "select", "values": [ "K", "°C", "°F" ] }, { "key": "rise", "label": "Water temperature rise", "value": 40, "type": "number", "min": 0, "step": "any" }, { "key": "days", "label": "Days per year", "value": 365, "type": "number", "min": 0, "max": 366, "step": 1 } ], "registrationFamily": "home-heating-costs", "input": true, "live": false, "presentation": "metrics", "inputMaxLength": 100000, "inputErrorCode": "HOME_HEATING_COSTS_TOO_LONG", "note": "Calculated on your device for up to 30 heater options and 100,000 characters. Enter efficiency or COP, input-energy standby loss and tariff for each option.", "inputKeywords": [ { "id": "home-heating-costs/water-heater-cost-comparison/options.header", "kind": "header", "code": "HOME_HEATING_COSTS_HEATER_HEADER", "fold": "lower", "values": { "option": [ "option", "Option" ], "type": [ "type", "Type" ], "fuel": [ "fuel", "Fuel" ], "efficiency": [ "efficiency", "Efficiency" ], "standby": [ "standby", "Standby" ], "tariff": [ "tariff", "Tariff" ] }, "describedBy": [ "Name the columns Option, Type, Fuel, Efficiency, Standby and Tariff, in that order, or leave out the header row.", "Heater options" ] }, { "id": "home-heating-costs/water-heater-cost-comparison/options.type", "kind": "cell", "code": "HOME_HEATING_COSTS_HEATER_TYPE", "fold": "exact", "values": { "Storage": [ "Storage" ], "Instantaneous": [ "Instantaneous" ], "Heat pump": [ "Heat pump" ] }, "describedBy": [ "Use Storage, Instantaneous or Heat pump in the Type column.", "Type" ] } ], "experience": { "automatic": false, "single": false, "inputMaxLength": 100000, "inputMode": "text", "label": "Heater options", "placeholder": "Stored electric,Storage,electricity,0.8,1,0.2", "help": "One option per line: name, type, fuel, efficiency or COP, standby input kWh/day and price per input kWh. Up to 100,000 characters. Review the settings before running.", "action": null }, "mode": "explicit", "interactive": false }, "execution": "Browser interface", "api": null, "browser_agent": { "supported": true, "name": "run_current_tool", "discovery": "WebMCP on the human page in a supporting browser", "verification": "See audit/API-AUDIT.md; availability is not verification" } } ``` ## Page guide Rank storage, instantaneous and heat-pump water-heater options by annual energy cost, using the same hot-water demand and your efficiency, standby-loss and tariff assumptions. ### How to use Water heater cost comparison 1. Enter daily hot-water volume, temperature rise and days of use. 2. Enter one option per line: name, Storage/Instantaneous/Heat pump, fuel, efficiency fraction or COP, standby input kWh/day and price per input kWh. 3. Check that standby is not already included in the efficiency figure you entered. 4. Review annual energy, cost and ranking, then download the JSON report and comparison CSV. How can we improve this tool? Report a problem or share an idea. Please leave out private information. Your message and the tool name go to our team via PostHog. ## Useful next steps - [Appliance electricity cost calculator](https://happytails.ai/en/calculators/appliance-electricity-cost-calculator/) ([Markdown](https://happytails.ai/en/calculators/appliance-electricity-cost-calculator.md)) - [Hot water energy calculator](https://happytails.ai/en/calculators/hot-water-energy-calculator/) ([Markdown](https://happytails.ai/en/calculators/hot-water-energy-calculator.md)) - [Insulation calculator](https://happytails.ai/en/calculators/insulation-calculator/) ([Markdown](https://happytails.ai/en/calculators/insulation-calculator.md)) ## Equal water demand Useful heat is litres × 4.186 × temperature rise in K / 3600 for each day. Water density is approximated as 1 kg/L and specific heat as 4.186 kJ/(kg K). Daily volume and temperature rise are the same for every option. ### Efficiency and standby For storage or instantaneous heaters, enter efficiency as a fraction, such as 0.9 for 90%. For a heat pump enter COP, such as 3. Standby is purchased input energy in kWh/day, added after useful heat is divided by efficiency or COP. Enter 0 if it is already included in your performance figure. ### A cost comparison Fuel and heater labels do not assign performance. Options are ranked by annual energy cost rounded to two decimals, with ties retaining input order. Installation, maintenance, standing charges, delivery speed and capacity are outside this estimate.