What Does a Whole-Home Generator Power?

A whole-home standby generator powers whatever the transfer switch is wired to cover, which on a properly designed system means the air conditioning, the heat, the well pump, the septic pump, the refrigerators and freezers, the internet, the security system and the gate, the kitchen and the home office. The limits are set at design time, not by the machine.

That is the part most buying guides skip. Two houses with identical generators can behave completely differently in an outage, because one has a whole-panel transfer switch with load management and the other has a small load center covering eight circuits somebody picked in a hurry.

Three ways a house gets covered

Essential circuits

A sub-panel is fed through a load-center transfer switch, and a set of circuits is moved onto it: the well, the furnace blower, the refrigerator, some lights and receptacles, sometimes one air conditioner. Everything else stays dark. It is the least expensive path and it works well, as long as the household agrees to the list in advance and lives with it on day four.

Managed whole home

A service-entrance-rated transfer switch backs the whole panel, and load management modules stop the largest loads from colliding. Every circuit in the house remains available. The system stages the compressors, holds the water heater while the well pump starts, and sheds the shop if capacity gets tight. For most properties this is the best coverage per dollar, and it is the design we recommend most often.

Unmanaged whole home

The whole panel again, but with the generator sized so that everything can run simultaneously with nothing coordinating it. No compromises and no cleverness. It costs the most, because the machine has to survive a worst case that will probably never occur.

System by system, what actually stays on

Cooling and heating

The reason most people buy. In July it is the compressor; in a hard freeze it is the furnace or the heat pump. Gas heat is a small electrical load, essentially just the blower and controls. Electric heat is not: a bank of resistance strips is one of the largest continuous draws in the house, and it has to be declared during sizing or the system will disappoint you in February.

Water

On a well, this is not a convenience item. The pump, the pressure tank and any booster or filtration equipment go on the backed-up side, and the pump’s starting surge frequently sets the size of the whole system. The full argument is in our guide to wells during outages. An electric water heater is a large load that is usually managed rather than dropped, so you get hot water without letting it compete with the air conditioner.

Wastewater

Aerobic septic systems need their aerator running and their effluent pump working, and houses below their tank need a lift pump. These are small loads that people forget, and forgetting them on a well property produces water going in with nothing pumping it out.

Refrigeration

Kitchen refrigerator, garage refrigerator, chest freezers. Individually modest, collectively significant, and the loads with the clearest dollar value attached to keeping them running.

Kitchen

Microwave, dishwasher, small appliances and the range. An electric range or double oven is one of the biggest single loads in a modern house, so it is almost always a managed load. In practice that means you can cook, and the system will not let you cook while three other large things are also running.

Internet, Wi-Fi and phones

Routers, modems, mesh points and cell boosters are trivial electrical loads and disproportionately valuable during an outage. Whether you actually get service depends on your provider’s equipment holding up, but powering your side of it costs almost nothing.

Security, cameras and gates

Alarm panels, cameras, network video recorders, garage door openers and driveway gate operators. The gate is the one people appreciate most, because a powered gate on a long drive is the difference between leaving the property and not.

Medical equipment

Oxygen concentrators, CPAP machines, powered beds, dialysis and refrigerated medication. If anyone in the household depends on powered equipment, it belongs at the top of the must-run list and it should be discussed explicitly, not assumed. Electric cooperatives themselves advise members with life-support equipment to have backup generation ready.

Home office and work

Computers, monitors, network gear and printers are small loads. If you work from home, an outage stops being an inconvenience and starts being lost income, which changes the arithmetic on the whole project.

Barn, shop and livestock

Stock tank heaters, waterers, ventilation fans, feed equipment, lighting and the shop. Some of this is genuinely critical, particularly livestock water in summer. Most of it is a strong candidate for load management rather than for a larger generator.

What does not come back on

Being straight about the limits is more useful than a list of everything that works.

• Anything on a circuit the design did not cover. On an essential-circuit system this is most of the house, and it is the single most common source of disappointment. Read the covered-circuit list before you sign, not afterwards.
• The first ten to thirty seconds. The transfer switch confirms the outage, starts the engine, waits for stable voltage and frequency, then transfers. Lights go out and come back. Desktop computers reboot, and anything sensitive wants a UPS or battery storage, which carries the load with no gap at all.
• Loads the manager is holding. If the water heater is being held while the compressors run, it is off for those minutes. That is the system working, not failing.
• Services that depend on somebody else’s power. Your router has power. Whether the neighborhood equipment feeding it does is a separate question.
• Anything already broken. A generator restores electricity. It does not fix a failed well pump, a failed compressor or a panel that was already at the end of its life, which is occasionally why an electrical panel upgrade is part of the project.

How to decide what must run

The exercise is simpler than people expect. Walk the house and sort everything into three buckets.

1. Must run, no discussion. Water, wastewater, refrigeration, heat or cooling, medical equipment, and the internet if you work from home.
2. Should run, can wait a few minutes. Range, oven, dryer, water heater, dishwasher. These are the classic managed loads: available, but not all at once.
3. Can wait for the utility. Vehicle charging, the pool, the shop, the hot tub. Shed first, restored last, and nobody minds.

That list, plus the nameplate data from the equipment, is what a load calculation is built on. It is also what makes two competing proposals genuinely comparable, because you can check each one against the same set of requirements. Our sizing guide covers the arithmetic, and the cost guide covers what moves the price once the list exists.

If you want that done properly at your property, the standby generator installation page sets out how we run the project, and requesting an estimate starts with the site visit rather than with a price over the phone.