Methodology

Reviewed by WattCostLab Editorial Team

How WattCostLab turns user inputs into transparent planning estimates.

Core principles

• Show the equation whenever practical.
• Keep important assumptions editable.
• Separate energy consumption from monetary cost.
• Use ranges and scenarios where a single number would be misleading.
• Do not present planning estimates as contractor quotes.

Electricity

kWh = Watts × Hours ÷ 1,000

Energy cost = kWh × electricity rate

Solar

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 pumps

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.

Updates

Methodologies should be reviewed when tariffs, incentive structures, standards or major market conditions change.