Whole-House Generator Guide: Sizing, Cost and Transfer Switches

Start with what must stay on

Whole-house generator questions are really load questions. Nobody needs every circuit in the house during an outage; they need heat, refrigeration, a sump pump, a well pump, communications and lighting. Once that list exists, sizing becomes a calculation rather than a guess.

The number that decides the size is not the total wattage on paper — it is the largest starting surge, usually from an air conditioner, well pump or furnace motor. A generator that handles the running load but not the surge will stall every time the compressor starts.

2026 cost bands

These are electrical installation bands. The generator unit, pad, fuel line and gas permits are usually separate line items.

• Manual transfer switch and inlet box for a portable: $800 - $2,500
• Automatic transfer switch only: $1,800 - $4,500
• Standby system electrical install, 22-26 kW: $4,000 - $9,000
• Larger standby systems, 30-48 kW: $7,000 - $18,000
• Generator sub-panel with load management: $900 - $3,000

The transfer switch is the safety device

A transfer switch physically disconnects your home from the utility before the generator supplies power. Without it, generator current flows backwards onto utility lines and endangers line crews — which is why backfeeding through a dryer outlet with a makeshift cord is both illegal and lethal.

Automatic transfer switches handle the switchover themselves within seconds of an outage. Manual switches cost less but require someone to be home and to operate them correctly.

Portable, standby or battery?

A portable generator with a manual transfer switch is the budget option, but it depends on fuel storage and someone being home to start it. A standby generator runs on natural gas or propane, starts by itself and carries long outages comfortably.

Home batteries are the third option. They switch over instantly and run silently, but their duration is measured in hours rather than days, so they suit short outages and pair well with a smaller generator for extended ones.

Questions to ask an installer

• What load calculation did you use, and what surge did you size for?
• Which circuits are on the generator panel, and is the AC or well pump included?
• Who handles the gas or propane connection and its permit?
• Do you file the electrical permit and manage the inspection?
• How is the system exercised and maintained, and at what interval?
• What happens to the warranty if I skip annual maintenance?