Method

Intensity

For each hour: Σ(fuel MWh × factor) ÷ Σ(all generation MWh). Factors (lb CO2/kWh, EIA, 2023): coal 2.31, natural gas 0.96, petroleum 2.46; nuclear, wind, solar, hydro, storage and other are counted as zero. Negative values (storage charging) count as zero generation.

Today's dial

EIA publishes hourly data with a delay of several hours. The dial averages the latest available days (up to 3) by hour of day and converts to your time zone. It shows a typical recent pattern, not a forecast of today.

A run

kWh = kW × hours. CO2 = kWh × the average intensity across the hours it runs. "Less" compares your start time with the best start time for the same length of run.

Cost

Flat rate: your state's average residential price (EIA). Time-of-use: the prices and hours you enter.

Limits

Power flows between regions; imports are not counted. Your utility's actual mix and your own rooftop solar are not included. Grid regions are matched by state, so near a border yours may differ; pick it from the list.