A whole-house standby generator ($6,000–$18,000 installed; most homeowners $10,000–$15,000) is the answer if outages are frequent or multi-day, you must automatically run central AC and/or a 240 V well pump — especially both at once — or you need power while away: it starts in ~10 seconds on an automatic transfer switch and runs indefinitely on natural gas. A portable ($450–$2,500 for the unit) covers essentials — fridge, furnace blower, sump/well pump, some lights — for short outages, but you must connect it through a UL-listed interlock or transfer switch(never a “suicide cord”) and accept manual setup and refueling every 8–12 hours. Either way, size it by running watts plus your single largest starting surge.
The choice starts with sizing, not price. Add up what you must run and your largest motor surge with the free generator size calculator, and confirm your panel with the electrical load calculator. Then this page helps you pick the machine.
⚖️ Standby vs. Portable at a Glance
Head to Head
| Factor | Portable | Whole-house standby |
|---|---|---|
| Capacity | ~3.5–10.5 kW | ~10–26 kW |
| Powers | Essentials; AC or well pump | Whole house, AC + pump together |
| Transfer | Manual interlock / switch | Automatic (~10 s) |
| Fuel | Gasoline / dual-fuel | Natural gas / propane |
| Runtime | 8–12 h per tank, refuel | Indefinite on natural gas |
| Operation | Manual; must be home | Automatic; runs while away |
| Installed cost | $450–$2,500 + $400–$900 hookup | $6,000–$18,000 |
Prices last reviewed August 2026. Generator costs swing with unit size, fuel source, gas-line distance, panel upgrades, permits, and regional labor (and spike after big storms). Treat these as wide national ranges, not quotes — get three itemized local bids.
⚡ What each can actually power
Size is where portables and standby units really diverge — because of starting surges. A motor draws two to three times its running watts for a second or two at startup, and those surges don't overlap on a standby (it staggers motor starts with automatic load management) but theystack on a portable. A 3-ton central AC can need ~8,500 starting watts; a 1 HP well pump 3,000–6,000. Try to start both at once on a 10 kW portable and it stalls or trips.
Size on running watts + your single largest surge — not the sum of every surge. That's the number the generator size calculator produces, and it's why an under-sized portable is the #1 reason people find their generator “won't start the AC.” A soft-start kit on the AC (~$100–$350) can cut its surge enough to drop a generator size.
So a portable realistically covers a chosen set of essential circuits plus one big 240 V load; a standby is sized to carry the whole house, AC and pump and range and EV together. If your must-run list includes AC and a well pump running at the same time, that alone usually points to standby (or a 10–13 kW portable with a soft-start kit and manual load sequencing).
🔌 How each connects — and the deadly shortcut
A standby uses an automatic transfer switch that senses the outage, starts the generator, and switches the house over in about 10 seconds — then switches back when utility power returns. A portable uses a manual transfer switch or a UL-listed interlock kit with a power inlet — a slide plate that physically stops the main breaker and the generator breaker from ever being on together. The interlock is the cheapest legitimate option and fits most panels installed since 2000.
Never use a “suicide cord.” A double-male cord from a running generator into a wall outlet is illegal and can kill. It backfeeds your panel, and the utility transformer steps that 240 V up to 7,200 V+ on the line — electrocuting a lineman who thinks the wire is dead. The exposed prongs are live, and it bypasses your breakers entirely. The NEC (702.5) requires listed transfer equipment precisely to prevent this. Always use an interlock or transfer switch, installed with a permit.
A standby install is a permitted job for a licensed electrician (and usually a gas fitter) — pad, gas line, transfer switch, inspection. A portable-plus-interlock is a smaller permitted electrical job. Both need the permit and the listed hardware.
⛽ Fuel & runtime
This is the day-two-of-the-outage difference. A standby on natural gas runs indefinitely with no refueling and no attention; on propane, a 500-gallon tank lasts roughly a week at half load. A portable burns through a tank of gasoline every 8–12 hours, so a multi-day outage means a fuel stockpile, hot-engine cool-downs, and refueling in the middle of the night. Gasoline also goes stale in months (about a year with stabilizer).
Dual-fuel and tri-fuel portables add flexibility — propane stores indefinitely, and a natural-gas hookup gives a portable near-unlimited runtime too. If you have gas service, that's a strong nudge toward either a standby or a tri-fuel portable on natural gas.
💰 Cost, up front and ongoing
The gap is large. A portable runs $450–$2,500 for the unit, plus $400–$900 to have an electrician install a UL-listed interlock kit and inlet box. A whole-house standby is $6,000–$18,000 installed — most homeowners land $10,000–$15,000, and a 22 kW natural-gas unit on an existing gas line is commonly around $9,500–$12,500 turnkey. The spread is driven mostly by kW size and install complexity: fuel source, gas-line distance, a possible panel upgrade ($1,500–$4,000 for 100→200 A), permits, and regional labor.
Ongoing, a standby needs $200–$600 a year in service (a dealer contract runs about $150–$300), plus fuel — natural gas is the cheapest and completely hands-off. A portable has little standing cost but real fuel logistics during an outage.
Don't buy a standby on resale value. A whole-house generator may recoup part of its cost at sale (strongest in storm-prone markets), but the data is thin and location-dependent — justify it on reliability and convenience, not ROI.
Prices last reviewed August 2026. Generator costs swing with unit size, fuel source, gas-line distance, panel upgrades, permits, and regional labor (and spike after big storms). Treat these as wide national ranges, not quotes — get three itemized local bids.
🏠 Living with it — and carbon-monoxide safety
A standby is automatic: it works whether or not anyone's home, which matters for travel, medical loads, and preventing frozen pipes or a failed sump. A portable must be rolled out, positioned, started, connected, and refueled by hand — and does nothing if you're away. Standby units are pad-mounted (not easily stolen) and weather-enclosed; a portable is exposed and a theft target during an outage.
Carbon monoxide is the portable generator's deadliest hazard — roughly 100 deaths a year (CPSC). Always run a portable outdoors, at least 20 feet from any window, door, or vent, with the exhaust pointed away — never in a garage, shed, or basement, even with the door open. Choose a unit with automatic CO shutoff (certified to PGMA G300 or UL 2201). A standby, permanently sited and vented outdoors per code, largely removes this risk.
✅ The bottom line
Choose a portable if outages are short and infrequent, you only need essentials, budget is the constraint, and you'll be home to run it — connected through a proper interlock and refueled safely. Choose a standby if outages are frequent or long, you must run central AC and/or a well pump (especially together), you want hands-off automatic power including when away, or someone depends on electricity for medical needs. A middle path exists: a 10–13 kW dual-/tri-fuel portable on an interlock covers an AC or a well pump plus essentials for far less money.
Whatever you choose, size it first, connect it through listed transfer equipment (never a suicide cord), and run a portable only outdoors well clear of the house. Codes and adopted NEC editions vary — confirm with your AHJ and use a licensed electrician (and gas fitter) for the install. Start with the generator size calculator.
Estimate your Generator Size materials
What size generator do you need? Free calculator from the loads you want to back up — running watts, motor-starting surges, and sizing headroom.
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