A standby generator is the difference between an outage and an inconvenience. It sits outside on a pad, watches your utility power around the clock, and — ten to thirty seconds after the grid fails — starts itself, transfers your house, and runs everything from the well pump to the Wi-Fi until the utility returns. No extension cords, no refueling in the rain at midnight, no carbon monoxide roulette in the garage. I've specced and serviced standby units through ice storms and wildfire shutoffs, and the pattern is always the same: the families who sized correctly barely notice the outage, and the ones who guessed at wattage spend it in the dark anyway. This guide covers sizing math, fuel choices, transfer switches, installation code, and the maintenance schedule that keeps a standby unit ready for the day you actually need it. Our standby generator lineup includes the Generac and Cummins residential series referenced throughout.
Sizing by Load: Calculating the Right Size for Your Home
Standby generators are rated in kilowatts of continuous output — and unlike portable units, the number on the badge is the number you can plan around, because these machines run on utility-grade fuel supplies and are engineered for multi-day continuous duty. Sizing starts with a load audit: list what must run during an outage, total the simultaneous running watts, add the largest motor's starting surge, and apply 20–25% headroom. The full audit method — appliance tables, NEC 220.83 demand factors, worked examples — is in our home wattage sizing guide. Here's the short version translated directly into generator sizes:
| Home / Load Profile | Typical Simultaneous Load | Peak With Motor Surge | Recommended Standby Size | What It Runs |
|---|---|---|---|---|
| Small home, essentials only (gas heat) | 2,500–4,000 W | 4,000–6,000 W | 10 kW | Fridge, furnace blower, sump, lights, Wi-Fi, some outlets |
| Medium home, no central AC | 4,500–6,500 W | 7,000–9,000 W | 14 kW | Essentials + well pump, kitchen circuits, home office |
| Medium home with 3-ton central AC | 6,500–9,000 W | 10,000–12,500 W | 18 kW | Most of the house incl. one AC compressor (soft-start recommended) |
| Large home, two AC units or all-electric | 10,000–14,000 W | 15,000–20,000 W | 22–26 kW | Whole home with load management on EV charger / water heater |
| Estate / small commercial | 16,000–25,000 W | 25,000–35,000 W | 30–48 kW | Multiple HVAC systems, elevators, server rooms |
Two sizing notes from the field. First, a soft-start kit on the AC compressor cuts starting current 60–70% and routinely moves a home down one generator size — the cheapest capacity you'll ever buy. Second, load-management modules (smart breakers or the transfer switch's built-in load shedding) let a smaller generator run a bigger house by deferring the water heater, dryer, and EV charger while the AC is running. Our deeper whole-house generator guide covers managed versus unmanaged whole-home strategies, and this sizing walkthrough applies the math to a real floor plan.
Fuel Options: Natural Gas, Propane, and Diesel
Fuel choice is usually decided by what's already at the house — but the numbers differ enough to matter when you have options.
| Attribute | Natural Gas | Propane (LP) | Diesel |
|---|---|---|---|
| Supply | Utility piped — effectively unlimited runtime | On-site tank (250–1,000 gal typical) | On-site tank (base or day tank) |
| Output derate vs. rated | Units are rated separately per fuel; NG output typically 5–10% below LP on dual-fuel models | Full rated LP output | Full rated output |
| Consumption at half load (≈ 20 kW class) | ≈ 200–250 ft³/hr | ≈ 2.0–2.5 gal/hr | ≈ 1.2–1.6 gal/hr |
| Consumption at full load (≈ 20 kW class) | ≈ 300–400 ft³/hr | ≈ 3.0–3.8 gal/hr | ≈ 1.8–2.4 gal/hr |
| Runtime on 500-gal LP tank (usable 400 gal), half load | — | ≈ 6–8 days continuous | — |
| Cold-weather behavior | Excellent; pressure must hold under load (meter sizing matters) | Tank vaporization rate drops in deep cold — oversized tanks or heaters needed below −20 °F design temps | Fuel gelling requires winter blend/additives below ≈ 10 °F |
| Storage / shelf life | N/A | Indefinite | 12–24 months untreated; polish or treat for longer |
| Best fit | Suburban homes on utility gas — the default choice | Rural properties without gas service | Commercial, large residential, long-run missions |
The natural-gas detail that bites installations: meter and regulator capacity. A 22 kW unit at full throttle pulls 300+ cubic feet per hour, and if your meter was sized for a furnace and a water heater, the generator can starve the whole house of gas pressure. We verify meter capacity with the gas utility on every NG install before setting the pad — it is a fifteen-minute phone call that prevents the single most common commissioning failure I see. Propane installs need the opposite check: tank size and vaporization rate at your design temperature, plus a first-stage regulator sized for the generator's full-load BTU demand.
Selection Criteria: Features and Specs to Compare in 2026
- Engine platform: purpose-built overhead-valve genset engines (Generac G-Force, for example) versus converted automotive blocks — purpose-built wins on valve-adjustment intervals and low-oil protection.
- Alternator: brushless with < 5% total harmonic distortion for clean power to electronics; digital voltage regulation ±1%.
- Controller: Wi-Fi monitoring with utility-sensing, exercise scheduling, and maintenance alerts is now standard on mid-tier and up.
- Enclosure: aluminum for coastal air, galvanized steel inland; sound ratings of 63–67 dBA at 23 ft on current quiet models.
- Warranty: 5-year limited is the residential standard; check whether labor is included years 1–2 only or throughout.
- Certifications: UL 2200 listing and EPA/CARB emissions compliance; required by many AHJs and all of California.
Installation Basics: Planning, Permits, Location, and Code References
A standby install touches four trades: sitework (pad), gas (fuel line and regulator), electrical (transfer switch and feeders), and permitting (AHJ plus utility notification). Budget one to two days of on-site work after the pad cures.
Location rules that show up on every inspection: NEC 445 and the manufacturer manual govern clearances — typically 18 in. minimum from the structure, 5 ft from operable windows, doors, and fresh-air intakes (NFPA 37/110 and local amendments vary; many inspectors enforce the window rule hard), and out from under bedroom windows where practical. The unit needs a level pad — precast composite or poured concrete — and a service path wide enough for the enclosure panels to come off. The NEC compliance guide covers the electrical articles (250 grounding, 702 standby systems, 300 wiring methods) as inspectors apply them.
Transfer Switches and System Integration
The automatic transfer switch (ATS) is the brain of the installation. It senses utility failure, signals the generator to start, waits for stable voltage and frequency, then transfers the house — and reverses the sequence when the grid returns, including a cool-down run for the engine. Two architectures dominate:
| ATS Type | What It Switches | Typical Sizes | Best For | Notes |
|---|---|---|---|---|
| Service-rated (whole-house) | The entire service entrance, ahead of the main panel | 100 A / 200 A (e.g., our 100 A service-rated ATS) | Whole-home backup, one-box installs | Includes the service disconnect; pairs with load-shedding modules for smaller generators |
| Sub-panel / essential-loads ATS | A selected set of circuits moved to a backup sub-panel | 50–100 A, 8–16 circuits | Smaller generators, budget installs | You choose the circuits at install; changing them later means moving breakers |
| Smart/load-management switches | Whole service with per-circuit software control | 200 A with managed modules | All-electric homes on mid-size generators | Defers EV charger, water heater, and dryer automatically under load |
Interlocks and backfeed are not a standby topic — a listed ATS is the only correct transfer means for a permanently installed unit, and NEC 702.5 requires it. Non-negotiable.
Noise, Emissions, and Environmental Considerations
Modern air-cooled residential units run 63–67 dBA at 23 ft under load — conversation level, roughly a central AC condenser. Liquid-cooled 25 kW+ units are often quieter at partial load because their engines turn 1,800 RPM instead of 3,600. Check local noise ordinances for nighttime limits and property-line measurement points; a corner-lot placement that satisfies the building code can still violate a noise covenant. Emissions-wise, all current residential units are EPA certified; CARB-compliant models are mandatory in California and a few aligned states. Exercise cycles (the weekly self-test) run 5–12 minutes and can be scheduled mid-day to keep the peace with neighbors.
Code Compliance, Permits, and Regional Incentives
Expect two permits — electrical and mechanical/plumbing (gas) — plus an HOA sign-off in governed communities. The electrical inspection covers the ATS installation, grounding per NEC 250, and feeder sizing; the gas inspection covers pipe sizing (CSST vs. black iron, bond per NEC 250.104(B)), shutoff placement, and sediment trap. Some utilities require notification for generators above certain sizes even though standby units don't parallel with the grid. A handful of states and insurers now offer resilience incentives or premium discounts for permitted standby systems — check current programs alongside our state incentives roundup, which tracks the adjacent solar-plus-storage rebates that often stack in the same jurisdictions.
Maintenance, Warranty, and Service Planning
A standby generator is a car engine that sits outside for years and must start on the worst night of the year. Maintenance is not optional, and it is not complicated:
| Interval | Task | Who |
|---|---|---|
| Weekly (automatic) | Self-test exercise cycle, 5–12 min; verify no alarms in the app | Unit + owner glance |
| Monthly | Visual: enclosure clear of debris/snow, no leaks, vents open, indicator green | Owner, 5 minutes |
| Every 6 months / 50 hrs | Battery check and terminal torque; firmware updates if offered | Owner or service plan |
| Annually / 100–200 hrs | Oil and filter change, air filter, spark plugs per manual, valve clearance check (first service and per interval), full-load transfer test | Service tech recommended |
| Every 2–3 years | Coolant (liquid-cooled units), belts, hoses; LP regulator inspection; battery replacement (typical life 3–4 years) | Service tech |
The battery is the number-one no-start cause — generators die of neglect, not overwork. A $90 battery every three years and an annual oil service is the entire reliability program for most air-cooled units. I tell customers to schedule the annual service in the fall, before storm season, because every service company in the region is booked solid the week after the first big outage. In our own service logs, roughly seven out of ten emergency no-start calls trace back to a battery that was older than four years — it is the cheapest reliability insurance on the whole machine.
Cost of Ownership and Market Trends
| Component | Typical Range (2026) | Notes |
|---|---|---|
| 10–14 kW unit | $3,500–$5,500 | Air-cooled, essentials coverage |
| 18–22 kW unit | $5,500–$8,000 | Whole-home sweet spot |
| 26 kW+ unit | $8,000–$14,000 | Large/all-electric homes |
| ATS (service-rated 200 A) | $600–$1,500 | Often bundled with the generator |
| Installation (pad, gas, electrical, permits) | $3,000–$7,000 | Gas-line length and panel distance drive the range |
| Annual maintenance | $200–$500 | DIY oil service at the low end, full service plan at the high |
| Fuel per outage day (NG, half load) | $25–$60 | Varies with gas tariff and loading |
Market-wise, residential standby demand keeps climbing with grid-storm frequency, and the trend line is toward smarter switches and hybrid resilience: generator + battery systems where a small battery carries the first minutes and overnight quiet hours while the generator handles bulk recharging — our hybrid inverter platforms with generator inputs, like the EG4 and Sol-Ark units, are built for exactly that pairing. Browse the full generator catalog or the home standby section for current models and lead times.
Smart-Home Integration and Outage Planning
Current controllers expose status, fuel (LP) level, exercise history, and fault codes over Wi-Fi, with push alerts when an outage starts and ends. Pair that with a simple household outage plan: know which loads shed automatically, keep the freezer closed, and don't test the generator's limits by starting the dryer mid-outage. For homes with medical devices, ask us about UPS bridging for the transfer gap — ten seconds is an eternity for a CPAP without a battery backup.
Regional Considerations, Climate Resilience, and Future-Proofing
Altitude derates air-cooled engines roughly 1% per 300 ft above ~3,000 ft on many models — a 22 kW unit in Denver is effectively a 19–20 kW machine, so size up at elevation. Coastal installs want aluminum enclosures and stainless hardware. Cold climates want battery warmers and, for LP, generous tank sizing against vaporization limits. Hurricane corridors want the pad anchored and the gas line protected. And if solar is in your five-year plan, tell your installer now: choosing a hybrid-ready electrical layout today (or adding a solar-plus-storage kit later) turns the generator from the whole answer into the backup's backup, which is where it runs the fewest hours and lasts the longest.
Frequently Asked Questions
What size standby generator do I need for a 2,000 sq ft home?
With gas heat and no central AC, a 10–14 kW unit covers essentials plus kitchen and office circuits. Add a 3-ton central AC and you're in 18 kW territory (or 14 kW with a soft-start kit on the compressor and load management). The load audit in our wattage guide gives your exact number.
Natural gas or propane — which is better for a standby generator?
Natural gas wins on convenience: unlimited runtime, no tank, no refills. Propane wins where there's no gas service, storing indefinitely on-site. Dual-fuel units run on either, typically producing 5–10% less output on natural gas.
How long can a standby generator run continuously?
Natural-gas units: indefinitely with scheduled oil service every 100–200 run hours. Propane units: until the tank empties — a 500-gallon tank typically carries a 20 kW-class unit six to eight days at half load.
Does a standby generator need a transfer switch?
Yes — a listed automatic transfer switch is required by NEC 702.5 for permanently installed standby systems. It is also what makes the system automatic: utility sensing, generator start, transfer, retransfer, and cool-down all happen in the ATS/controller pair.
How loud is a home standby generator?
Current air-cooled models measure roughly 63–67 dBA at 23 feet under load — comparable to a central air conditioner. Liquid-cooled units running at 1,800 RPM are often quieter at partial load.
