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Whole-Home Backup vs Essential Loads: Sizing a Backup System
Do you want the whole house on backup, or just the essentials? The difference changes battery size, inverter power and cost dramatically.
WaterFuelAndSolarEnergy.com Editorial Team Updated December 2024 8 min read
“Whole-home backup” sounds ideal, but backing up every circuit — including A/C, oven and EV charger — requires a much larger battery and inverter than backing up just the essentials. Know which you actually need.
Backup scope compared
| Scope | Typical loads | Battery size needed |
|---|---|---|
| Essential loads | Fridge, lights, router, small electronics | ~5–10 kWh usable |
| Partial home | Essentials + one appliance (e.g. heating) | ~10–15 kWh usable |
| Whole home | Everything, incl. large appliances | ~15–25+ kWh + big inverter |
The essential-loads approach
The smart and cost-effective route is a “critical loads” sub-panel that keeps selected circuits on backup. This dramatically cuts battery and inverter cost while covering what matters most in an outage.
Can one battery back up a whole house?
Rarely for large loads. Most single home batteries back up essential or partial-home circuits unless paired with a large inverter and multiple units.