Backup power is only as good as the circuits on it. Too few and the outage is miserable — food warms, the furnace sits, a sump does not run. Too many and the generator or battery cannot carry the list: the transfer trips, or you stand at the panel turning things off in the dark.
The list is the design:
refrigeration, heat, a well or sump, medical equipment, enough light to live — not the EV, the range, or the whole house by default
The question that decides it is not “Can I back up the whole house?” It is which circuits genuinely have to stay on, and whether the source you actually have — or will buy — can carry that list without back-feeding the utility. That list is the design of a critical-load panel. The generator or the battery is a separate purchase. Which kind of source is generator vs battery backup; the circuits themselves are the question here.
Quick answer: which circuits belong on backup power?
Start from how the house is actually used, not a generic kit. Most Sacramento homes that back up a subset, not the whole service, land some combination of the refrigerator (and a freezer, if it is a separate circuit), the furnace blower or heat-pump air handler, a well pump or a sump if the property has one, medical equipment that cannot wait, and enough lighting plus a receptacle circuit to live. Most jobs do not put an EV charger, an induction range or electric dryer, a tankless water heater, a hot tub or sauna, a workshop welder, or every lighting circuit in the house on that list. The total has to fit the source. A longer list needs a bigger machine — or a shorter list.
| Load | Usually on the backup list? | Why |
|---|---|---|
| Refrigerator / freezer | Yes | Food. Ready.gov: a closed fridge holds about four hours; a full freezer about 48. |
| Furnace blower / air handler | Often | Gas heat still needs the fan. The outdoor compressor is a different, larger load. |
| Well or sump pump | If you have one | No water, or a wet basement, is not an inconvenience — it is the outage. |
| Medical equipment | If it cannot wait | CPAP, oxygen, a hospital bed. Ready.gov: if you need power to stay healthy, have a plan to leave. |
| Selected lights and outlets | Yes | Enough to live. Not every chandelier. |
| Router / communications | Often | Only if that circuit is small and you actually need it. |
| EV charger | No | A large continuous load. It waits. |
| Range, dryer, tankless | No | Nameplate loads that swallow a portable set by themselves. |
| Whole-house A/C compressor | Usually no on a small source | Starting current. Air handler ≠ outdoor unit. |
The list is the design of the panel
A critical-load panel is a subpanel that holds only the circuits that have to stay on. Those circuits are moved onto it. A transfer method feeds it without connecting the utility and the backup together. The feeder, the subpanel, and the source are sized to that list — with headroom only where it is deliberate.
Backing up everything is a larger transfer and a bigger machine, wired at the main. That is a different job. Start at transfer switch if the whole house is the goal and the machine can carry it. Most portable generators cannot.
Whole-house backup is a real product: a standby generator and a transfer at the main, sized to the service. It is also a much larger machine and a much larger electrical job. A subset is the usual Sacramento portable-generator or battery path: a critical-load panel, a listed transfer, a source that can carry the short list. If you want the whole house, say so. Do not build a twelve-circuit “essentials” panel and then add the range later.
Which machine to buy is generator vs battery — a different question — and this is not a dryer-outlet workaround, solar, a reason to assume 200 amps, or a DIY map for moving breakers. The electrical structure is critical-load panel work. The source connection is backup power. A new subpanel and transfer are permit-required work; see what electrical work requires a permit.
Should the refrigerator be on backup power?
Food is why most lists start here. Ready.gov: keep the doors closed. A refrigerator holds about four hours. A full freezer about 48. Throw food out if it has been at 40°F or higher. That is preparedness. The electrical question is whether the fridge circuit is on the backup panel so those hours do not start.
A refrigerator often shares a kitchen circuit with other receptacles. If that circuit also carries a microwave, a toaster, and half the island, putting “the kitchen” on backup may be more load than the fridge. Sometimes the honest backup is a dedicated refrigerator circuit, or moving only that receptacle — not the whole kitchen run. The fridge is the load. The rest of the run may not belong.
Heat: the blower is not the compressor
A gas furnace still needs electricity for the blower, the controls, and often the ignition. That is a modest motor compared with the outdoor heat-pump or A/C compressor. People say “HVAC” and mean both. On a small portable generator, the air handler may belong on the list and the compressor may not.
A heat-pump house in a Sacramento summer is a different conversation: cooling is comfort until it is safety. The outdoor unit’s starting current is why the source and the list are decided together. Do not assume the furnace circuit is only the furnace. Lighting or a garage door on the same breaker changes the picture. Name the blower and the compressor separately — different currents, different decisions — not as one “HVAC” line on the list.
Well, sump, and medical equipment
If the property has a well, no backup on that pump means no water once the pressure tank empties. A sump that does not run in a storm is a flooded space, not a dark kitchen. Those are the circuits that make the list worth building. Name them first, not after the panel is already laid out.
Medical equipment that cannot wait belongs on the list if the household is staying. Ready.gov is also plain: if you need power for medical devices to stay healthy, have a plan to go somewhere that still has it. Backup electrical is not a substitute for that plan. Name the actual equipment. “Medical” is not a circuit label in the panel.