Whole-Home vs. Partial-Home Backup: How to Decide
Most homes don’t need whole-home backup. A partial (critical-loads) setup that keeps your refrigerator, Wi-Fi, lights, and a few outlets running costs a fraction of a whole-home system and covers what actually matters during a typical outage. Whole-home backup earns its higher price only in specific situations: loads you truly can’t pause, frequent multi-day outages, or a property where seamless power is part of the value.
What each option actually means
Whole-home backup keeps every circuit in your electrical panel live when the grid goes down, including central air conditioning, electric ranges, and other heavy 240-volt equipment. That takes a lot of stored energy: whole-home systems commonly start around 30 kWh of battery capacity, roughly one day of electricity for an average U.S. home, and installed costs typically run $25,000 to $50,000 or more.
Partial-home backup, which electricians call a critical-loads setup, protects only the circuits you choose. Your must-run loads move to a small subpanel, and a battery in the 5 to 15 kWh range carries them through an outage. Installed systems generally land between $8,000 and $20,000, and at the smallest scale a portable power station does the same job with no electrician at all.
Start with the outage you’re actually planning for
According to the U.S. Energy Information Administration, the average U.S. electricity customer lost power for about 11 hours in 2024, the most in a decade, and hurricanes caused 80 percent of it. Set major storms aside, and routine service interruptions average about two hours per year.
That gap is the whole decision. If your area sees short, occasional outages, a partial setup, or even a portable unit, covers nearly all of them. If you live where hurricanes, ice storms, or wildfire shutoffs regularly take the grid down for days, longer-duration backup starts to justify its cost.
The case for partial backup (most homes)
Add up what you actually need in an outage and the list is usually short:
Refrigerator and freezer, protecting food and medications
Wi-Fi and phone charging, staying informed
Lights in the rooms you use most
Medical devices such as a CPAP
A garage door opener, sump pump, or the fan on a gas furnace
Together those typically draw well under 1,500 watts. A mid-sized battery carries them for many hours, and partial systems are also expandable: most modern batteries accept added capacity later, so you can start right-sized and grow only if your outages prove longer than expected.
When whole-home backup makes sense
Whole-home backup is the right call in a narrower set of circumstances:
You rely on medical equipment and cannot tolerate any gap in power
A well pump, sump pump, or electric heat must run through extreme weather
Your area sees frequent multi-day outages
You want central air conditioning through extended summer outages, which alone can draw 3,000 to 5,000 watts
Seamless power is part of the property’s value, as in a rental or premium listing
One caveat before you triple the battery: some of these loads, a well pump for instance, can often be covered by a well-designed partial system with a single 240-volt circuit. A good installer will price that option first.
How to decide in five steps
List the loads you genuinely cannot pause, with their running watts.
Check your utility’s outage history for frequency and typical duration.
Size the battery to those loads and hours, not to your panel’s full capacity.
Price a partial system and a whole-home system side by side, and compare what each dollar actually protects.
Confirm equipment certifications and local code compliance before you buy.
If you would rather not work through that alone, this is exactly what our vendor-neutral process is built for.
Frequently asked questions
Can a partial-backup system run central air conditioning?
Usually not. Central air conditioning draws 3,000 to 5,000 watts or more, plus a startup surge, which pushes you into whole-home territory. A window unit or an efficient mini-split on a backed-up circuit is the practical middle ground.
Do I need an electrician for partial backup?
For a wired critical-loads subpanel, yes. For plug-in options like a portable power station, no. That is the renter-friendly path, and it requires no permit or panel work.
How big a battery do I need for partial backup?
Add up the running watts of your protected loads, then multiply by the hours you want to cover. Essentials drawing 1,000 watts for ten hours need about 10 kWh of usable capacity.
Is whole-home battery backup better than a standby generator?
Neither is better in every case. Batteries are silent, fuel-free, and pair well with solar, but very long outages test their capacity. Generators run as long as they have fuel but need maintenance and permits. In regions with multi-day outages, some homes pair a partial battery with a small generator.
Sources: U.S. Energy Information Administration on 2024 outage duration, and EnergySage on whole-home backup batteries.
