Pick the circuits you want alive during an outage and get a recommended generator size, battery bank, and transfer-switch rating — computed live as you go.
How this is calculated
Each load has running watts (steady draw) and surge watts (the spike a motor pulls the instant it starts, often 2–4× running). Fridges, freezers, pumps and furnace blowers surge; LEDs, routers and most electronics don’t.
Peak load isn’t the sum of every surge number — loads don’t all start at once. It’s total running watts plus the single biggest surge-minus-running gap (usually the well pump) — that’s the worst instant a generator or inverter actually has to survive.
Battery bank size is total running watts × hours, divided by usable depth of discharge — about 80% for lithium (LiFePO4), 50% for lead-acid, so a lead-acid bank needs roughly 60% more capacity for the same runtime.
Transfer-switch amps is total running watts divided by panel voltage (240V split-phase in the US, 230V single-phase in Europe) — the continuous current the switch and its wiring must be rated for.
- All selected loads are treated as running the entire backup window — a worst-case estimate. Pumps and furnace fans actually cycle, so real battery runtime is usually longer than shown.
- Generator and switch sizes round up to the nearest common off-the-shelf size, not the raw math — you can’t buy a 5.28kW generator.
- Defaults are typical values, not your house — edit any wattage field to match your own appliance labels.
Want the full walkthrough first? Read what size generator to back up a whole house.
What we’d actually buy
Generator kW on one side, battery kWh on the other — these are the pairings we’d pick from. Picked on merit from what’s on the market right now — street prices, checked July 2026.
- Honda EU2200i — 2.2kW inverter generator, 48 dB — the essentials-only benchmark that starts every time. $1,000–1,200
- Westinghouse iGen8200TFc — 8.2kW-peak tri-fuel (gas / propane / natural gas) inverter unit — panel-scale backup with clean output. $1,100–1,500
- EcoFlow DELTA Pro 3 — the silent half of a hybrid setup — battery carries the night, generator only runs to recharge. $2,700–3,000
Chosen on merit — nobody paid to be on this list, and several of these can never earn us a penny. If a link here ever earns Grid CEO a referral fee, it will say so — disclosure.
- Honda EU22i — 2.2kW inverter generator, the quiet-start benchmark. €1,300–1,600
- EcoFlow DELTA Pro 3 — the silent half of a hybrid setup — battery carries the night, generator only recharges it. €2,800–3,500
Chosen on merit — nobody paid to be on this list, and several of these can never earn us a penny. If a link here ever earns Grid CEO a referral fee, it will say so — disclosure.
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