Plan Backup Power Around What Needs to Keep Running

Before asking how big a generator needs to be, we start with a different question: what can you not afford to have stop working? At home, that might be the refrigerator and heating equipment. On a farm, it might be a well pump. For a business, it might be the equipment that keeps the doors open.

The useful starting point is the consequence of losing power, not the square footage of the building. A backup plan should account for what needs power, what it takes to start that equipment, and how long it needs to operate. Here is how we approach those questions.

Make three lists before choosing equipment

Start by separating electrical loads into three groups:

• Must keep running: the equipment you cannot afford to have stop working.
• Can run occasionally: equipment that needs power, but does not need to operate continuously.
• Can wait: equipment you can leave off while the essentials take priority.

Consider water, refrigeration, heating equipment, essential medical devices, communications, and business-critical equipment. These are prompts, not a ready-made priority list. The point is to identify which loads belong in each group for your home, farm, or business.

We would rather begin with those priorities than with a generator size. Saying that you need to keep a well pump operating gives the planning process something concrete to work with. Saying that you want backup power for a building still leaves the important question unanswered: what actually needs to keep running inside it?

Size for starting demand as well as running power

Starting equipment can take more power than keeping it running. Pumps and refrigeration compressors can require extra starting power, so adding up the numbers on appliance labels is not the whole sizing process.

Proper sizing considers starting demand, voltage, and which loads operate together. That last piece brings us back to the three lists. Equipment that can run occasionally still needs to be accounted for when it operates alongside the must-run equipment.

Before moving toward generator installation, we want the planning conversation to stay centered on those actual loads. The useful question is what needs to start and run together during an outage, not how much equipment you own.

Treat food storage as a planning deadline

Refrigeration puts a time limit on an outage plan. With the doors closed, a refrigerator can keep food cold for about four hours. A full freezer can maintain temperature for roughly 48 hours, or about 24 hours when half full.

Those are planning estimates, not a substitute for checking food temperatures. We would not treat the clock alone as confirmation that food is still at the right temperature.

Use those estimates to decide where refrigeration belongs on your lists and how many hours of backup power it needs. Food storage gives an outage a deadline, so plan around that deadline.

Plan for operating hours as well as watts

A power requirement does not answer the whole backup question. We also need to ask:

• How long must the essential equipment run?
• What fuel or stored energy is available?
• Who can operate the system if you are away?

These questions belong alongside equipment sizing, not after it. That holds for a generator and for battery backup systems alike: keep the required operating time in view. Identifying the essential loads is one part of the plan; identifying how long they need power is another.

Include safety in the plan

Portable fuel generators belong outdoors, at least 20 feet from doors, windows, and vents, and never in a garage. Use battery-backed carbon monoxide alarms, and have a qualified electrician handle any connection to building wiring.

We keep those points in the same conversation as loads and operating time. A backup plan should say where the equipment will run and who will connect it, as well as what it can power.

Before shopping, spend 10 minutes identifying your five most important electrical loads. If you want a starting point for reviewing your home's readiness, take our free Home Resilience Assessment.

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