The assumptions stay visible.

Monthly kWh = watts ÷ 1,000 × hours used per day × days used per month. Monthly cost = monthly kWh × electricity price per kWh.

Reference data: the U.S. Energy Information Administration publishes electricity sales and average prices by state and sector. The U.S. Department of Energy explains EnergyGuide operating-cost comparisons.

Important limit

Rated watts can overstate average consumption for equipment that cycles or changes speed. Metered use is better when available.

We compare two five-year scenarios. The repair path includes the quote and five years of current energy cost. When remaining expected life is less than five years, it also includes a later replacement. The replacement path includes the purchase price and five years of new-unit energy cost.

This intentionally does not invent a universal reliability score. Labor rates, parts, warranties and actual condition are local and appliance-specific.

Usable Wh = rated capacity × system efficiency × (1 − reserve percentage). Runtime hours = usable Wh ÷ average load watts.

Surge loads, inverter cutoffs, battery age and temperature can materially change real-world performance. The result is for planning, not a performance guarantee.