Most home energy confusion comes from mixing up watts and kilowatt-hours.
Watts are the speed of energy use. Kilowatt-hours are the amount of energy used over time. A 100-watt device running for 10 hours uses 1,000 watt-hours, or 1 kWh.
The formula
Use this:
watts x hours = watt-hours
Then divide by 1,000:
watt-hours / 1,000 = kWh
A 60-watt router and network setup running for 24 hours uses 1,440 Wh, or 1.44 kWh. A 1,500-watt appliance running for 20 minutes uses about 0.5 kWh. Short high-power loads and long low-power loads both matter.
Continuous, intermittent, and surge loads
Continuous loads
These run for long stretches: routers, medical equipment, aquarium gear, some fans, and standby electronics.
Intermittent loads
These cycle: refrigerators, freezers, sump pumps, dehumidifiers, and heat pumps.
Surge loads
These draw extra power at startup: pumps, compressors, motors, some power tools, and some appliances. Surge affects inverter sizing even when total energy use looks reasonable.
How to measure
Use device labels, manuals, smart plugs, a plug-in power meter , utility data, or a whole-home monitor. For 240V appliances, do not improvise measurement. Use labels, professional data, or manufacturer documentation.
Why this matters for every upgrade
| Upgrade | What the math decides |
|---|---|
| Portable power station | Runtime and surge capability |
| Home battery | Usable capacity and backed-up circuits |
| Solar panels | Daily production target |
| EV charger | Circuit capacity and charging speed |
| Heat pump | Electrical load and comfort strategy |
| Induction range | Circuit needs and cooking load |
Tiny homes make this math obvious because the systems are smaller. The same load-list habit appears in Tiny Home Solar Power Sizing .
The useful habit
Make a household load list once. Keep it in a note. Every future energy decision becomes easier because you are comparing equipment against your actual life, not a generic marketing scenario.
