Whole-home vs critical-loads backup
The biggest decision in home battery backup is what the battery should power when the grid is down.
How the parts connect is covered in How home backup works.
| Critical-loads backup | Whole-home backup | |
|---|---|---|
| What runs in an outage | Selected circuits moved to a separate backup subpanel (for example the fridge, lights, internet, well pump or furnace fan) | The main panel, so any circuit can run, within the battery and inverter's limits |
| Battery and inverter size | Smaller, because fewer loads run | Larger, especially to start big motors such as central AC or a well pump |
| How long it lasts | Longer on the same battery, because less is running | Shorter on the same battery unless you turn loads off |
| Installation | Rewiring circuits to a subpanel | A transfer switch or backup gateway at the main service |
How to choose
- List what you need during an outage and its watts.
- Estimate the energy over the hours you want to cover (Power basics).
- Check the largest single load and its starting surge against the inverter's rating.
- Get quotes for both options; costs vary by home and installer.
Note: the federal 25D residential clean energy credit does not apply to systems installed after December 31, 2025 (IRS). Check state and utility programs.
Home backup installs need a licensed electrician, permits and usually utility approval. Not professional advice.