This is the other way a business bill jumps without the business changing. In the distillery case the demand line rose and the energy line fell. Here the energy line more than doubled while the peak moved only by the size of the new load, and the whole explanation is in the one number a bill never prints: how much the building draws at 3 AM.
Two winters, same building
A seasonal retail site in ComEd territory, one meter, three years of 30-minute data. Its busy season is summer: 8,000 to 10,000 kWh a month from June to August, dropping to a quarter of that in the cold months. The first winter in the record looks like a building mostly asleep. The second does not.
| month | usage | overnight floor |
|---|---|---|
| December 2023 | 2,685 kWh | 1.2 kW |
| January 2024 | 2,801 kWh | 1.3 kW |
| February 2024 | 2,394 kWh | 1.1 kW |
| December 2024 | 6,350 kWh | 5.8 kW |
| January 2025 | 6,736 kWh | 6.0 kW |
| February 2025 | 5,641 kWh | 5.7 kW |
The overnight floor is the demand the building never drops below: the fifth percentile of every half hour in the month, which in practice is the quietest hours of the night. In the first winter it was about 1 kW, the standby load of a closed building. In the second it was nearly 6 kW, and it stayed there through May 2025.
The arithmetic of a floor
A floor of 5.8 kW running for every hour of a 30 day month is 5.8 times 720, or about 4,200 kWh. That single always-on load is larger than the building's entire usage in any month of the previous winter. Against December 2024's 6,350 kWh, the floor alone accounts for about two thirds of the month.
The rest of the picture confirms it. Summer usage barely changed between the two years, 8,800 and 9,800 kWh in June and July 2024 against 8,700 and 10,300 in 2025, so the business did not get busier. The winter peak rose from 13 to 14 kW to 18 to 23 kW, which is roughly the new floor stacked on top of the old peak. That is exactly what a flat load does: it lifts every half hour by the same amount and leaves the shape alone, so the demand line rose by about half while the energy line rose by about 130 percent. And it does not show up in the season the building is already running hard. It shows up as a winter bill that doubled for no visible reason.
When it started, and what the meter cannot say
The floor stepped up in two moves: from 1.8 kW in October 2024 to 2.3 kW in November, then to 5.8 kW in December, and it held near 5 to 6 kW for at least the next six months. So something began running continuously in November 2024 and something more joined it in December.
What those things are, the meter does not know. Electric heat left on in a space that used to be unheated, a heat trace or freeze protection circuit, a new refrigeration unit, a well or sump pump running constantly, a failed thermostat holding a heater on: each is a flat 24 hour load, and each is invisible on a bill except as a bigger number. The interval data narrows the search to a month and a size, about 4 to 5 kW of continuous draw arriving in late 2024. Finding the equipment is a walk through the building with that number in hand.
Why the bill could not have said this
A bill shows kWh for the month and kW at the peak. A doubled winter kWh figure with a peak up by half is consistent with dozens of stories, and the bill picks none of them. The floor picks one: a load that runs when nothing else does. That is why the first thing worth reading in any building's interval data is not the peak but the quietest half hour, and why the free usage analysis we run on a ComEd export reports the always-on floor before anything else. On this building, that one number is the whole story of the winter bill.
We have not reconciled a bill for this site, so there is no dollar figure here, only kilowatt hours. The energy went from roughly 2,600 to 6,200 a month for a season, and every one of those extra kilowatt hours was bought at the supply rate for a load nobody chose.
What is the overnight floor on an electricity meter?
The demand a building never drops below, read from the quietest half hours of the month. It is what runs when the building is closed: refrigeration, standby equipment, anything left on. It is not printed on a bill.
Can a bill double without the business changing?
Yes. A load of about 5 kW running continuously adds roughly 4,200 kWh to a 30 day month. On a building that used 2,600 kWh in winter, that more than doubles the energy line while the summer usage stays where it was and the peak rises only by the size of the load.
Why did the demand charge move less than the bill?
Because a flat load adds its own size to the peak and nothing more. About 5 kW of continuous draw on a building that peaked at 13 to 14 kW lifted the winter peak to 18 to 23 kW, roughly 50 percent, while the energy line rose about 130 percent. Continuous loads show up mostly on the energy line.
How do I find what is running overnight in my building?
Read the floor from your interval data, note the month it changed and its size in kW, and then walk the building looking for something of that size that never switches off. The meter gives the when and the how much; the building gives the what.