Choose a quiet comparison window
Look for several periods when cooking, laundry and optional entertainment are inactive. Record whether heating, cooling, water heating or refrigeration still operates. An unoccupied apartment is not an electrically inactive apartment.
Utility interval downloads can help locate repeated patterns. PG&E’s customer tools are one example; check your own provider’s data units and availability. Use comparable windows rather than the lowest isolated point on the chart.
Calculate an average over the window
Suppose a six-hour overnight period uses 0.90 kWh. Average power is 0.90 ÷ 6 = 0.15 kW, or 150 W. If that average persisted for a full 30-day month, it would use 108 kWh and cost $19.44 at $0.18/kWh.
That monthly result is a projection, not proof of a constant 150 W load. A refrigerator or heater may cycle, and daytime conditions can change its use. Compare several nights before choosing a working estimate.
Build a short device inventory
List refrigeration, networking, clocks, standby electronics and any required building or safety equipment. Add credible measured or documented energy estimates where available. Do not assume the entire unexplained remainder is waste.
Use normal controls only for optional devices that can be safely switched off, one change at a time. Do not disable essential medical, safety, food-storage or required ventilation equipment to force the meter toward zero.
Investigate a material unexplained change
Compare a new pattern with your own previous baseline, noting weather, guests and new equipment. A persistent step change may justify checking settings or requesting maintenance. If meter assignment is a concern, ask the provider or property manager to investigate; do not open panels or alter wiring. The useful deliverable is a dated set of observations and plausible questions, not an accusation based on one overnight graph.
Choose your next step
Continue with the question that matches your next decision:
Sources & further reading
Numerical examples are illustrative unless explicitly described as measured. This guide does not claim hands-on product testing. Read the methodology and editorial disclosure.