Use a filled worksheet to separate unlike nights
Every kWh entry in this filled worksheet is an invented teaching value. The rows are not meter observations from a household and do not claim typical fan use. They show why an average becomes misleading when the speed or number of fans changes.
Scroll horizontally to see all columns.
| Night | Setup | Hours | Example kWh entry | Use in low-speed average? |
|---|---|---|---|---|
| A | One fan, low | 8.0 | 0.40 | Yes |
| B | One fan, low | 7.5 | 0.38 | Yes |
| C | One fan, low | 8.25 | 0.42 | Yes |
| D | One fan, high | 8.0 | 0.61 | No; speed changed |
| E | Two fans, low | 8.0 | 0.82 | No; a second fan was added |
Average only the three matching worksheet rows
Worksheet rows A, B, and C describe one fan on low speed for roughly the same sleep period. Their average is (0.40 + 0.38 + 0.42) / 3 = 0.40 kWh per included night. At an illustrative rate of 0.16 per kWh, one matching night costs 0.40 x 0.16 = 0.064, displayed as 0.06. If the rate is in dollars, that result is 0.06 dollars; use the equivalent unit for another currency.
Do not enlarge the average with rows that answer a different question. Row D represents the high setting, and row E represents two fans. Each would need its own label and result in a real log.
Use watts only when the fan pattern is stable
Without measured kWh, an illustrative 50 W input sustained for 8 hours gives 50 / 1,000 x 8 = 0.40 kWh. This fallback is defensible only when the selected wattage matches the speed used and the fan does not materially change power during the night. A speed change should be split into separate time blocks or measured across one clearly timed session.
Before projecting another night
Before extending the result, write down the fan count, speed, start and stop times, included nights, and rate. Then multiply by the number of future nights that genuinely match those conditions. This is more informative than calling every summer night an average fan night.
The 0.40 kWh worksheet average represents the included mix of 7.5- to 8.25-hour nights, not an exact eight-hour measurement. If you need a fixed duration and draw is stable, divide the combined 1.20 kWh by the combined 23.75 hours before multiplying by the target hours. For eight hours that is about 0.404 kWh, still an estimate from invented values. Keep the unrounded cost of 0.064 per included night when scaling the original average.