How whole house generator installation works

A whole house generator installation is more than dropping a unit in the yard: it's a load calculation, a pad, an automatic transfer switch wired into your panel, a fuel-gas connection, permits, and inspection. In short: a licensed electrical and gas job from start to finish. Here's exactly what happens, how long it takes, and what it costs, so you know what you're buying before an installer ever knocks.

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The seven steps of a generator install

Whether it's a Generac, Kohler, Cummins, or Briggs & Stratton unit, and whether you're hooking up a generator to natural gas or propane, a proper standby generator installation follows the same sequence:

Site assessment and load calculation. The installer visits, adds up the circuits you want backed up, measures the starting surge of your AC and well pump, and confirms your gas meter can feed the unit. That load calculation sets the kilowatt size and where the generator can legally sit — typically a few feet from windows, doors, and the gas meter per the manufacturer and local code.
Permit application. The installer pulls an electrical permit — and usually a mechanical/gas permit — with your city, township, or county building department. A reputable installer does this as part of the job; treat anyone who suggests skipping permits as a red flag.
Pad and placement prep. A level concrete or composite pad goes down where the load calculation placed the unit, with the code-required clearances around it for airflow and service access.
Setting the generator. The unit is moved onto the pad and anchored. An air-cooled whole house generator is roughly the size of a central AC condenser; a liquid-cooled unit for a large home is bigger and heavier and may need a small crane.
Wiring the automatic transfer switch. The automatic transfer switch is wired between your meter and main panel. It is the heart of the install: it disconnects your house from the utility before starting the generator, which is what keeps power from backfeeding onto the grid and endangering line crews. This is licensed electrical work in every state.
Fuel hookup. A natural gas line is tapped and sized to the unit — often with a flexible connector and a sediment trap — or, off the gas main, a propane tank and regulator are plumbed in. The line is pressure-tested before the generator ever runs.
Inspection and commissioning. The building department inspects the electrical and gas work. Then the installer starts the unit, tests the transfer under load, sets the weekly self-exercise schedule, and connects monitoring so you get an alert if it ever fails to start.

The automatic transfer switch, in plain terms

It's the one part of a home generator installation most homeowners have never heard of, and it's the part that matters most. The automatic transfer switch constantly watches the utility line. When the power drops, it disconnects your house from the grid, signals the generator to start, and switches your panel over — all within seconds, with no one home. When utility power returns, it reverses the process and shuts the generator down. That grid disconnect is not optional: without it, a running generator can push power back up the line and electrocute the crew working to restore it. It's why "installing a generator to your house" is never a plug-in job.

Fuel: natural gas vs. propane hookup

Most whole house generators run on natural gas or propane. A natural gas hookup for a generator taps your existing gas line — the installer has to confirm the meter and piping can deliver enough volume for the unit, and will usually run a correctly sized line with a flexible connector and a sediment trap, then pressure-test it. Off the gas main, a propane tank and regulator do the same job, with runtime capped by the tank. Diesel is a niche for very large homes with on-site fuel storage. Fuel choice is settled during the site visit, alongside sizing.

Permits and inspection — and what's in force where you live

Every state we cover requires an electrical permit and inspection for a generator install, and requires the electrical work to be done by a licensed contractor — no exceptions. The National Electrical Code is the floor; the exact edition in force varies by state. Here's what applies in each state we cover, with the full permit-cost and timeline breakdown on each state's page:

Michigan — 2023 National Electrical Code with Michigan's Part 8 amendments, in force since March 12, 2024; one- and two-family homes also fall under the 2021 Michigan Residential Code.
Texas — 2023 National Electrical Code statewide (TDLR-adopted, effective September 1, 2023) — the minimum standard even where no permit is required; TDLR is set to move Texas to the 2026 NEC on September 1, 2026. Cities can layer local amendments on top.
California — 2025 California Electrical Code (Title 24, Part 3), based on the 2023 NEC, in force statewide since January 1, 2026 — alongside the 2025 California Building Code.
Florida — Florida Building Code, 8th Edition (2023), in force since December 31, 2023, with electrical work under the 2020 NEC as adopted by the code's Chapter 27. The 9th Edition (2026) takes effect December 31, 2026.
Georgia — The 2023 National Electrical Code with Georgia Amendments — the 2023 NEC took effect as the state minimum on January 1, 2025, and the 2026 Georgia Amendments to it took effect January 1, 2026. One- and two-family homes also fall under Georgia's adopted residential code.
North Carolina — The 2020 North Carolina Electrical Code, in force since November 1, 2021 — the National Electrical Code as amended by North Carolina. The 2024 North Carolina State Building Code has been repeatedly delayed; as of late 2025 its conditions for adoption were unmet, putting the earliest possible effective date at January 1, 2027, so 2020-cycle codes remain current.
Louisiana — The 2020 National Electrical Code, as amended by the LSUCCC, in force statewide since January 1, 2023 (alongside the 2021 editions of the IRC, IBC, IFGC, IMC, and IPC). Louisiana law requires the state to move to each new NEC within five years: the LSUCCC approved adoption of the 2023 NEC and the 2024 I-Codes on July 7, 2026, so an updated code edition is expected to take effect shortly — confirm which edition your parish is enforcing at permit time.
South Carolina — The 2020 National Electrical Code, adopted as part of the 2021 South Carolina building codes that took effect January 1, 2023. A 2024 code cycle is in the adoption pipeline at the Building Codes Council but is not yet effective, so the 2020 NEC remains the electrical code in force.
Tennessee — The statewide minimum is the 2017 National Electrical Code, adopted by the State Fire Marshal's Office, with Tennessee amendments (for example, AFCI protection is optional in certain rooms). Local jurisdictions may adopt a newer edition — some enforce the 2020 or 2023 NEC — and can be more stringent than the state floor, so confirm the edition with your local inspector.
Virginia — The 2020 National Electrical Code, adopted as part of the 2021 edition of the Virginia Uniform Statewide Building Code, which took effect January 18, 2024. Because the USBC is a statewide code, that same NEC edition applies in every county and city — a locality can't adopt its own.
Alabama — Residential wiring follows the 2021 International Residential Code (effective October 1, 2022), whose electrical provisions are based on the 2020 National Electrical Code; state-regulated buildings are on the 2020 NEC directly. Alabama has no single electrical code enforced in every jurisdiction, and residential code authority moved to the Home Builders Licensure Board in October 2024 — confirm the edition and whether a permit is required with your local building department.
Ohio — The 2023 National Electrical Code, adopted with Ohio amendments and effective March 1, 2024 for both the Ohio Building Code and the Residential Code of Ohio. It replaced the 2017 NEC that had been in force previously.
Mississippi — Mississippi has no single statewide residential electrical code; the National Electrical Code edition in force is whatever your local jurisdiction has adopted, and it can differ from one county to the next. Confirm the current NEC edition and permit requirements with your local building department before the install.
Kentucky — Kentucky adopts the National Electrical Code statewide as the minimum electrical standard (KRS 227.480), and HBC moved the state to the 2023 NEC with mandatory enforcement beginning January 1, 2025. For one- and two-family dwellings a handful of 2023 articles are phased in and defer to the 2017 NEC until mid-2026, so confirm the current requirements with your local inspector.
Pennsylvania — The Uniform Construction Code adopted the 2021 ICC code series effective January 1, 2026, which references the 2020 National Electrical Code. Pennsylvania's triennial review process runs several cycles behind the national code, so the 2020 NEC is current here even as newer editions exist elsewhere; confirm any local amendments with your code official.
New Jersey — The electrical subcode is the 2020 National Electrical Code (NEC), adopted at N.J.A.C. 5:23-3.16, which took effect September 6, 2022 as part of New Jersey's move to the 2021 ICC I-Code family. Because the UCC is a uniform statewide code, that same NEC edition applies in every municipality — a town can't adopt its own electrical edition.
New York — Outside New York City, the 2017 National Electrical Code, referenced by the 2020 New York State Uniform Fire Prevention and Building Code, which took effect May 12, 2020. New York City runs its own electrical code: the 2025 NYC Electrical Code (enacted by Local Law 128 of 2024), based on the 2020 NEC, took effect December 21, 2025 — so two different NEC editions are enforced within the state depending on which side of the city line the home sits.
Maryland — Maryland enforces the Maryland Building Performance Standards (MBPS), which adopted the 2021 IBC and 2021 IRC statewide effective May 29, 2023, with local jurisdictions required to adopt within 12 months (by May 29, 2024) and free to add local amendments. The National Electrical Code is not part of the MBPS — it is adopted at the county/municipal level, so jurisdictions currently enforce either the 2020 or the 2023 NEC. Confirm the edition and any local amendments with your county permit office.
West Virginia — The enforceable installation standard statewide is the 2020 National Electrical Code, adopted by the State Fire Commission effective August 1, 2022, alongside the 2018 editions of the IBC, IRC, IMC, and IPC. The State Fire Marshal moved its licensing examinations to the 2023 NEC as of January 1, 2026, but the code your install is inspected against remains the 2020 NEC until a new adoption cycle takes effect. Confirm the current edition with your local inspector.
Indiana — Indiana runs a notably lagging electrical code. The standalone Indiana Electrical Code (2009 edition, 675 IAC 17-1.8) still incorporates the 2008 National Electrical Code — roughly fifteen years behind the current model code — and an update to the 2023 NEC remains in committee rather than in force as of 2026. One- and two-family dwellings are governed by the Indiana Residential Code (based on the 2018 IRC), whose electrical provisions track a newer NEC than the standalone code, so confirm the exact edition your dwelling is inspected against with the local building department.
Missouri — Because there is no statewide code, the enforced edition of the National Electrical Code depends on the authority having jurisdiction. Kansas City enforces the 2017 NEC (effective June 28, 2020), and the City of St. Louis likewise lists the 2017 NEC alongside the 2018 IBC and IMC. Editions vary and can lag between neighboring jurisdictions, so confirm the current edition with the local building department.

How long it takes and what it costs

The install itself is typically a single day once the permit and equipment are in hand; the whole process usually runs two to six weeks, driven by permit turnaround and unit availability. Installed cost tracks the size and fuel: essentials-only units land around $6,000–$9,000, a whole house air-cooled unit runs roughly $9,000–$16,000 installed, and liquid-cooled units for large homes climb past $20,000. For a size and price tuned to your home, run the sizing & cost calculator — it estimates kilowatts and installed cost from your square footage, coverage level, fuel, and state.

By brand: Generac, Kohler, and the rest

The install sequence is the same across brands; what differs is the dealer and service network behind it. Generac has by far the largest dealer network, so a Generac generator installation — whether it's a Guardian air-cooled unit or a larger whole house Generac backup generator — usually means parts and warranty techs are close by, and the unit ships with Mobile Link monitoring. Kohler standby generator installation runs through a thinner but well-regarded dealer network, with strong load-management options. Cummins and Briggs & Stratton round out the field with solid air-cooled lineups. In every case the installer and the service relationship afterward matter more than the badge — which is why this directory classifies who actually specializes in each brand.

Browse installers by the brand they fit: Michigan , Texas , California , Florida , Georgia , North Carolina , Louisiana , South Carolina , Tennessee , Virginia , Alabama , Ohio , Mississippi , Kentucky , Pennsylvania , New Jersey , New York , Maryland , West Virginia , Indiana , Missouri .

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A licensed installer confirms the size with an on-site load calculation and quotes the whole job — unit, automatic transfer switch, gas work, permits, and inspection. Tell us about your project and we'll connect you with a qualified installer serving your area.

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Generator installation questions

Do I need a permit to install a whole house generator?

Yes — everywhere. A standby generator install involves panel work, an automatic transfer switch, and a fuel-gas connection, all of which require a permit and inspection. Every state we cover also requires the electrical work to be done by a licensed contractor. A good installer pulls the permits as part of the job.

How long does a generator installation take?

The install itself is usually a single day once the equipment and permit are in hand. The whole process — site visit, permit approval, unit delivery, install, and inspection — typically runs two to six weeks, driven mostly by permit turnaround and how quickly the unit is available.

Natural gas or propane — which hookup is better?

If a natural gas line already reaches the house, that is usually the answer: nothing to refill, and the generator runs as long as the utility keeps gas flowing. Propane is the standard where gas service doesn't reach — it needs a 250–500 gallon tank, which adds cost if you don't already have one, and your runtime is whatever the tank holds.

Can I install a standby generator myself?

No — and not only for safety. The panel work, transfer switch, and gas connection all need permits and inspection, and every state we cover requires the electrical work to be done by a licensed contractor. An improper install can backfeed the grid and endanger utility workers. This is exactly the job the installers in this directory do every week.

How far from the house does the generator have to sit?

The manufacturer sets minimum clearances — commonly around 18 inches off the wall and five feet from windows, doors, and other openings — and your local code and the gas-meter location can tighten that further. The installer settles the exact spot during the site visit; it is part of why the load calculation happens on-site rather than over the phone.

Is the installation cost included when I get a quote?

A turnkey installed quote covers the unit, the automatic transfer switch, the pad, gas or propane piping, electrical work, permits, and commissioning. Use the sizing & cost calculator for a planning range, then get a firm number from an installer's on-site load calculation.

Do I need an inverter generator for whole-house backup?

No — home standby generators are conventional (non-inverter) units that run at a fixed engine speed, and that is best suited for whole-house backup. Inverter generators are built for portable, on-the-go power. Generac systems offer True Power, which should keep total harmonic distortion low enough that your sensitive electronic devices should be fine. If you have sensitive devices, please raise this question with your installer to make sure you'll be covered.

Do I need whole-home surge protection with a standby generator?

It's a smart pairing. Power surges from lightning, grid demand spikes, or large appliances cycling on and off can permanently damage sensitive electronics. Generac installs can add that protection one of a few ways: a standalone Surge Protection Module that mounts at your breaker panel, an Automatic Transfer Switch with factory-integrated surge protection, or a Home Standby Generator bundle that pairs the generator with that surge-protected transfer switch for whole-home coverage in a single install.