The unit is often less than half the invoice. Our cost breakdown separates hardware, gas, electrical and permits so you can see which quote is padded.
See the installed cost breakdown →Installing a standby generator is less an appliance purchase than a small construction project. Two licensed trades, at least two permits, a pad, and a fuel supply that has to deliver more gas at once than your house has ever asked for. The crate on the driveway is the easy part. What follows is the sequence a real install goes through, where it stalls, and which decisions are yours rather than the installer’s.
What “Installed” Actually Includes
When a dealer quotes you a number, ask them to split it. A complete residential standby job has six cost centers, and they behave very differently from house to house:
- The generator itself — air-cooled units in the roughly 10 to 26 kW range for most houses, liquid-cooled above that.
- The transfer switch — either a whole-panel automatic switch or a smaller critical-loads switch. This is a real fork in the road; see transfer switch types and cost.
- The pad and site work — a composite pad on compacted gravel, or poured concrete if the ground is soft.
- The gas line — new pipe from the meter or tank, correctly sized, plus a shutoff and sediment trap.
- The electrical run — conductors and conduit from generator to switch, plus the control wiring.
- Permits, inspections and commissioning — including the first load test and setting the exercise schedule.
Sizing sits underneath all of it. A unit chosen to run the whole panel needs a bigger gas feed and a bigger switch than one chosen to run a well pump, a furnace, a fridge and some lights. Work out the load first, using the method in what size generator your house needs, and bring that number to the quote.
The Permits, and Who Pulls Them
Nearly every jurisdiction wants two permits: an electrical permit for the transfer switch and the feeder, and a mechanical or fuel-gas permit for the piping. Some add a zoning or building permit for the pad and the setback, and some rural counties want nothing beyond the electrical. Noise ordinances and HOA rules are a separate layer that no inspector will warn you about.
The licensed electrician pulls the electrical permit; the licensed gas fitter pulls the gas permit. You should never be the one pulling a homeowner permit for work someone else performs, because the liability lands on you. If a quote comes in far below the others and nobody mentions inspections, that gap is the permits. An unpermitted transfer switch is the kind of thing that surfaces at closing, or the first time you file an insurance claim after a house fire.
Setbacks: Five Feet Is the Number to Remember
NFPA 37, the standard for stationary combustion engines, puts outdoor engines and their weatherproof housings at least five feet from openings in walls, and at least five feet from structures with combustible walls. There are two written exceptions: walls within five feet carrying a one-hour fire rating, or an enclosure of noncombustible material demonstrated not to ignite anything outside it. Most manufacturers of enclosed air-cooled units qualify under the second exception, and then impose their own minimum of about 18 inches from the wall for airflow and service access.
The exception applies to the fire clearance. It does not make the exhaust harmless. Keep the discharge end pointed away from windows, doors, soffit vents, dryer vents, fresh-air intakes and window air conditioners, and treat any opening the manufacturer lists as a five-foot exclusion zone. A permanently installed generator is quieter and better behaved than a portable one, but it still burns fuel a few feet from your walls.
Safety: Passing inspection does not mean carbon monoxide cannot reach you. CPSC has documented CO deaths from permanently installed generators, usually where exhaust found an intake, a crawlspace vent or an open window. Working CO alarms on every level are part of the install, not an accessory. See generator placement and CO.
The Gas Line Is Where Projects Stall
This is the step homeowners never see coming. A whole-house generator running at load can demand roughly as much gas as the rest of the house combined. On natural gas, your existing meter and regulator were sized for a furnace, a water heater and a range — not for those plus an engine. The utility often has to swap the meter and the service regulator, and that is their schedule, not your installer’s. Ask about meter capacity before you sign anything; it is the single most common reason a two-day job becomes a six-week one.
Pipe sizing follows NFPA 54 and depends on total demand, run length and the number of fittings. A long run from a meter on one corner of the house to a generator on the other usually needs a larger diameter than the first estimate assumes. Undersizing is invisible at low load and ugly at high load.
On propane, the constraints change. NFPA 58 setbacks scale with tank size: aboveground tanks from about 125 to 500 gallons water capacity generally sit at least 10 feet from the building and the property line, and tanks above 500 gallons move out to 25 feet. Underground tanks are typically 10 feet regardless. Two more propane realities: a tank fills to about 80 percent, so a 500-gallon tank holds roughly 400 usable gallons, and a small or nearly empty tank in deep cold cannot vaporize liquid fast enough to feed an engine at full draw. Consumption varies by unit — figure on the order of two to three gallons per hour for a common air-cooled model at half to full load, and confirm against the actual spec sheet rather than a sales estimate.
Who Does What
| Task | Who does it | Permit / inspection |
|---|---|---|
| Site survey, setbacks, pad | Dealer or general contractor | Zoning or building, sometimes |
| Gas piping and shutoff | Licensed gas fitter or plumber | Mechanical / fuel-gas permit |
| Meter or regulator upgrade | Gas utility only | Utility work order |
| Transfer switch and feeder | Licensed electrician | Electrical permit |
| Startup, load test, exercise setting | Factory-authorized dealer | Required for warranty |
| Annual service | Dealer or competent owner | None |
The Order That Keeps It Moving
- Measure your real load and pick a size before you talk to a dealer.
- Call the gas utility about meter capacity, or your propane supplier about tank size and setback, and get the answer in writing.
- Choose the location with the installer on site, tape-measure in hand, checking every opening within five feet.
- Permits go in. Pad and gas rough-in happen while you wait for the utility.
- Electrical and switch, then inspections, then commissioning with an actual load test.
- Set the weekly exercise for a weekday mid-morning, not Sunday at seven.
Two Things That Go Wrong
The first is the undersized gas feed. The generator starts, runs the exercise cycle beautifully for months, and then shuts down twenty minutes into a real outage when the furnace, the well pump and the water heater all call at once. Fuel pressure sags, the engine stumbles, the controller faults. Homeowners spend money chasing a “generator problem” that is a pipe-diameter problem.
The second is placement chosen for appearance. Tucked against a fence for looks, and the unit overheats. Placed on the north side where snow drifts, and it is buried in February. Put under a bedroom window, and the weekly exercise becomes a standing grievance. Walk the site in the worst month you can imagine, not in June.
How I Would Approach It
Get three itemized quotes, each splitting gas from electrical, and refuse the ones that give you a single number. Confirm meter or tank capacity with the utility before you commit, because that answer can change the whole economics. Then look at the total honestly: if the gas work comes back at a few thousand dollars because the meter needs replacing and the run is long, price the alternative before signing. A portable generator with an interlock kit covers the same critical loads for a fraction of the money, at the cost of going outside in bad weather to start it. Standby is worth the premium if you travel, if someone in the house depends on power, or if you are on a well and outages run for days. It is a lot of money for convenience if your outages last two hours.
Frequently Asked Questions
Do I need a permit to install a whole house generator?
In almost every jurisdiction, yes — typically an electrical permit for the transfer switch and a mechanical or fuel-gas permit for the piping. Some areas add zoning review for the setback. The licensed trades pull them; you should not.
How far does a standby generator have to be from a window?
NFPA 37 sets five feet from openings in walls as the baseline. Manufacturers of enclosed air-cooled units typically also require about 18 inches of clearance from the wall itself for airflow. Follow whichever is stricter, and check the specific model’s installation manual.
Can I install a standby generator myself?
You can usually do the site prep and set the pad. The gas connection and the transfer switch require licensed trades in most places, and factory startup is normally a warranty condition. Doing the wiring yourself tends to cost more than it saves once the inspection fails.
How long does a standby generator installation take?
The physical work is two to three days. The calendar is usually four to ten weeks, driven by permit turnaround and by the gas utility if the meter or regulator needs upgrading.
Does a propane standby generator need a dedicated tank?
Not necessarily, but it usually needs a bigger one. A tank sized for a range and a dryer will run dry fast and may not vaporize quickly enough in cold weather. Many installs move from a 250-gallon tank to a 500-gallon tank, which also changes the required setback.