Choosing which circuits are worth backing up

The question gets asked as though it were technical. Which circuits should go on the generator.

It is really a budget question. Every circuit added raises the load, the load sets the generator, and the generator sets most of the cost. So the list is where the money is decided, and it is worth building deliberately rather than by instinct.

Four circuits do most of the work

Across most households, the same handful of things turn an outage from miserable into tolerable.

• The refrigerator, and the freezer if it is separate. Modest draw, and the thing that turns a long outage into a financial loss.
• The heating system, including its blower and controls, which need power even when the fuel is gas or oil.
• A sump pump, where there is one. This is the circuit that decides whether an outage during a storm also becomes a flooded basement.
• A well pump, where the house is on a well, since without it there is no water at all, including for sanitation.

That list is usually under 3,000 running watts, though the surges from the pumps push the requirement higher for a moment. It is well inside what a decent portable handles, which is why the middle-cost backup arrangements work for so many houses.

Then lighting and the sockets you actually use

After those, a lighting circuit and one or two receptacle circuits cover phones, laptops, a router and a lamp in the room everyone ends up sitting in.

These are cheap in watts and high in morale. A house with a working fridge and no lights feels like a crisis. A house with lights and wifi feels like an evening in.

The expensive tier

Air conditioning, electric range, electric water heater, electric dryer. Each one is thousands of watts, and any of them can double the generator you need.

That is the honest threshold between a portable-sized system and a standby-sized one. It is worth being explicit about which of those you are buying, because the jump is not incremental. Work the running and starting figures with the generator size calculator with and without the air conditioning, and the price of that one decision becomes visible before anyone quotes for it.

Circuits are not appliances

The practical complication is that you do not get to choose appliances, you choose circuits, and the house was wired without this question in mind.

Your fridge may share a circuit with half the kitchen. The furnace may be on a circuit that also feeds something irrelevant. A single room can be split across two circuits. So the first job is to open the panel, read the labels, and find out what is actually grouped with what, ideally by testing rather than by trusting the handwriting from 1994.

An electrician can move a circuit at install time, which is far cheaper than discovering after the fact that the backup list includes a garage socket and excludes the boiler.

Count the watts before choosing the count

Transfer switches come in fixed sizes, six, eight, ten or twelve circuits. The temptation is to choose the count first and allocate afterwards.

Better to total the load first. The home wattage calculator will take the candidate list and give the running total and the share each item contributes, which usually makes one or two items stand out as doing nothing for the total but costing a circuit.

Build the list before you need it

An outage is a poor time to discover that the sump pump is on the same circuit as the garage freezer you forgot about.

Write the list on paper, label the panel properly while the lights are on, and keep a note of which breakers to turn off before starting the generator. If the arrangement is a portable with an interlock, that sequence is something somebody has to do correctly in the dark, which is a strong argument for having written it down somewhere other than in your own head.