Reviewed by WattCostLab Editorial Team
How WattCostLab turns user inputs into transparent planning estimates.
kWh = Watts × Hours ÷ 1,000
Energy cost = kWh × electricity rate
Preliminary sizing is based on household energy demand, peak sun hours and a system-loss factor. Financial results are simplified unless a page explicitly models additional variables.
Heat-pump electricity use is estimated as delivered heat divided by seasonal COP. Actual performance changes with climate, equipment sizing, distribution temperatures, controls and backup heat.
Methodologies should be reviewed when tariffs, incentive structures, standards or major market conditions change.
Location and currency are independent. Location selects an official or regulatory energy reference when one is available; currency determines the monetary unit used by calculators. A reference is applied automatically only when its native currency matches the selected currency. Otherwise the user must enter a tariff in the selected currency. This prevents an electricity price reported in euros from being silently treated as the same numeric amount in dollars, rupees or lei.
Manual electricity and gas overrides are stored locally in the browser for the selected location/currency combination. They can be reset to the official reference at any time. The same energy-assumption layer is reused by solar, heat-pump, EV-charging and home-efficiency calculators. Water-heating and home-improvement pages show the location context even when project/contractor costs remain user-entered.
The Building Wall Heat Transfer Calculator uses a steady-state one-dimensional series thermal-resistance network with editable layer thicknesses, thermal conductivities and indoor/outdoor convection coefficients. Its scientific basis is the Energy Reports paper doi:10.1016/j.egyr.2020.08.055.
The Solid Fuel Combustion Calculator reproduces the published calculation sequence for stoichiometric oxygen, dry/wet combustion air and major flue-gas volumes from ultimate analysis and excess air. Its scientific basis is doi:10.1016/j.egyr.2019.10.016. The constants used by the calculator are intentionally preserved from that source model.
The Home Climate Adaptation Planner is a readiness and project-planning tool, not a geographic climate-risk model. The user selects concerns that are relevant to the property; WattCostLab does not infer that a property is exposed to heat, flooding, wildfire, storms or drought solely from its country or city.
The readiness score is intentionally transparent: completed applicable actions receive full credit, planned actions receive half credit, and not-yet or not-assessed actions receive no credit. Actions marked not applicable are excluded. The score does not estimate hazard probability, expected loss, property value, insurance risk or structural safety.
Project-cost and annual-benefit fields are user-entered. Climate-adaptation contractor prices are not automatically generated because scope, codes, building type and local market conditions vary materially. Existing WattCostLab cost calculators are linked where the scope overlaps with insulation, windows, HVAC, electrical upgrades or backup power.
Location is used to present official reference portals. WattCostLab does not currently convert Copernicus or other climate datasets into property-level future-risk estimates. The Copernicus Climate Data Store provides quality-assured climate datasets and API access, but property decisions require appropriate spatial resolution, scenario selection, bias adjustment/downscaling where applicable, local hazard mapping and building-specific information.
The Location Climate Intelligence layer uses the documented NASA POWER Monthly Point API for a fixed 1991–2020 period. WattCostLab calculates the 30-year monthly climatology from those monthly observations. The 1991–2020 period is consistent with the current 30-year climatological standard-normal period used by WMO for operational climate normals.
The automated core request retrieves NASA POWER monthly temperature data for 1991–2020 and calculates an arithmetic climatological mean for each calendar month. Mean wind and precipitation are requested separately so that an optional wind or precipitation failure does not break the temperature baseline. WattCostLab displays the annual context, warmest-month climatological maximum, coldest-month climatological minimum and annual mean 10 m wind when available. If an optional upstream variable is unavailable, the page reports it as unavailable rather than substituting invented data.
The heat-adaptation screening labels are WattCostLab planning heuristics based on the warmest-month climatological maximum temperature: lower below 25°C, moderate from 25 to 29.9°C, elevated from 30 to 34.9°C and strong from 35°C upward. These thresholds are not NASA, WMO, insurance, engineering or regulatory hazard thresholds. They are used only to decide whether heat-adaptation measures deserve review.
Mean wind is shown as baseline context and is not treated as a severe-wind or storm-risk indicator. Flooding, heavy rainfall, drought, wildfire/smoke and severe-storm exposure remain marked for local verification using official hazard maps or competent authorities. WattCostLab does not derive a property-level climate-risk score from the NASA POWER baseline.
The V16.17 comparator is a user-controlled comparison workspace. WattCostLab does not maintain a hidden proprietary ranking of suppliers and does not claim that its locally stored offer rows represent the complete live market. The user selects a market, imports an official/exported file where supported or enters a shortlist of offers manually, and the tool ranks only those rows.
If an imported or entered row contains a direct annual-cost estimate, that value is used as the comparable annual cost. Otherwise the tool estimates the comparable annual amount from the entered energy rate, annual electricity use and fixed monthly/annual charges. An optional first-year comparison can also include the entered exit fee. This simplified calculation is appropriate only when the inputs represent the same cost basis.
A supply-only offer must not be compared directly with an all-in household bill unless the user normalizes both to the same components. In U.S. retail-choice markets, competitive supplier prices commonly cover generation/supply while distribution and other utility charges remain on the local utility bill.
The comparator sorts by estimated comparable annual cost. Filters for rate type, renewable content, contract term and exit fee are applied after the cost calculation. Advertising, sponsorship or a future referral relationship cannot alter this ranking.
Offer currencies are market-native. WattCostLab does not silently FX-convert supplier prices when the site's independent global Currency setting differs from the market currency.