What is a whole-house generator?
Updated August 2026
A whole-house generator, called a standby generator in the trade, is a permanently installed engine and alternator that senses an outage, starts itself in about 10 seconds, and carries the house on natural gas or propane until utility power returns. Capacity is stated in kilowatts. Roughly 10–14 kW keeps a fridge, furnace, well pump, sump pump, and lights alive; 22–26 kW runs a typical 2,500 square foot house including central air conditioning.
Where it is
The generator sits outdoors on a composite or concrete pad, shaped like an oversized AC condenser and usually placed 18 inches off the wall with 5 feet of clearance to any window, door, or dryer vent. A flexible fuel line ties into the gas meter or a propane tank, and a conduit runs back to an automatic transfer switch mounted beside the electrical panel. That transfer switch, not the generator, is what most homeowners never notice: a steel box with a small display and, on many models, a manual override handle.
What it does
The transfer switch watches utility voltage continuously. When it drops for a preset few seconds, it signals the engine to crank, waits for the output to stabilize, then throws the house over. Start to lights back on is typically 10–30 seconds. On natural gas the runtime is unlimited; a 500-gallon propane tank supports about a week of intermittent load. When these units disappoint, they almost always fail at the start rather than during the run, and the ranked culprits are a dead battery, oil that sat five years, a clogged air filter, and a rodent nest in the enclosure. The weekly self-test exists precisely to surface those before a storm does.
Maintenance
Leave the weekly self-exercise cycle enabled, typically 12 minutes at a set day and time, and confirm it actually runs rather than assuming. Change oil and filter every 100–200 run hours or once a year, whichever comes first, and replace air filter, spark plugs, and valve-lash adjustment on the 2-year or 400-hour mark. Batteries last 3–5 years and cause more no-start calls than everything else combined. An annual dealer service visit runs $200–450.
What it costs to replace
A replacement whole-house generator runs $5,000–15,000 installed, including the transfer switch, pad, gas hookup, and permits.
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Frequently asked questions
What size standby generator do I need?
Two questions decide it: do you want essentials or the entire house, and how big is the air conditioner. An essentials build covering the furnace, refrigerator, well pump, sump pump, and a lighting circuit fits inside 10–14 kW. Adding one 3-ton AC compressor pushes you toward 18–22 kW, and a large home with two compressors and an electric range wants 24–26 kW. A load-management module can shed the AC during peak draw and let a smaller unit cover more house.
How much does it cost to run during an outage?
Fuel is the real number. A 22 kW unit at roughly half load burns on the order of 200 cubic feet of natural gas per hour, which at 2026 residential rates lands near $2.50–3.50 an hour, or $60–85 for a full day of running. Propane costs more, generally $3–6 an hour at the same load. A three-day outage therefore runs $180–450 in fuel, before any post-storm service call.
Is a standby generator worth it over a portable one?
It depends on how often the power quits and who is home. A portable unit plus a transfer switch costs $1,500–3,500 all in, but somebody has to be there, awake, and willing to fuel it every 8 hours. A standby unit costs three to five times as much and asks nothing of you. Homes with a well, a sump pump, medical equipment, or outages more than three or four times a year usually justify the jump.
How long do these units last?
Air-cooled residential models generally give 15–25 years or roughly 3,000 run hours, and liquid-cooled units go longer. Nothing about that is automatic: the units that reach 20 years are the ones that got oil changes, fresh batteries, and a clean enclosure. The ones that die at 8 years usually sat through a decade of weekly self-tests with the same oil and a corroded battery terminal nobody looked at.