Standby Generator Cost Calculator

For the most common whole-home setup — a 22 kW natural-gas unit with an automatic transfer switch on a 25 ft gas run — this calculator computes about $9,560 at national-average rates ($7,648–$12,906 end to end). Generac itself publishes $8,000–$16,000 installed including the generator, and HomeGuide's 2025–2026 data puts whole-house installs at $6,000–$11,000, rising to $9,500–$24,000 above 20 kW or with long utility runs.

HomeGuide's sizing bands: 13–16 kW covers a full home under ~1,500 sq ft, 17–20 kW covers 1,500–3,000 sq ft, and 22–25 kW covers 3,000–5,000 sq ft including central AC. Step up a size for a well pump, an EV charger or a large two-stage AC — and note that a service-rated whole-home ATS with load management (about $900 more on our 18 kW job) can let a smaller unit run the whole house by shedding loads in rotation.

The units themselves cost about the same on gas vs propane (HomeGuide lists both in the $2,000–$6,000 band), so the swing item is the tank: buying and setting a new 500-gal propane tank adds about $1,100 to our 18 kW job. Diesel hardware carries roughly a 60% unit premium — about $10,900 vs $8,660 installed at 18 kW here, with diesel skipping the gas line entirely — plus fuel-polishing upkeep. Propane's advantage: it's on your property and keeps flowing when utility gas lines are shut off in a disaster.

Price and code. A manual switch or interlock kit runs about $7,760 installed vs $8,660 for an automatic ATS on our 18 kW reference job — and some jurisdictions allow interlocks where autos fail inspection. But you lose the point of standby: someone must be home to flip the switch, in the dark, in a storm. Most dealers won't warranty a "standby" install on a manual switch for exactly that reason.

Yes — virtually everywhere. The electrical hookup always needs a permit, and the gas line needs a plumbing/gas permit with a pressure test. HomeGuide puts real permit fees at $80–$450 ($250 blended here). Dealers normally pull both as part of the job; an unpermitted install can void the manufacturer warranty, complicate insurance claims after a fire, and surface as a disclosure problem at sale.

The physical work is typically 1–2 days on site — pad, set the unit, run the gas line, wire the transfer switch, startup and load test — but that is the last week of a longer pipeline: site survey, electrical and gas permits with a pressure test, then utility gas-company signoff, each measured in weeks. Two practical accelerators: order the transfer switch from the same manufacturer as the unit (mixing brands complicates load-management wiring and warranty service), and settle the pad location and gas route during the survey, since re-staging is what turns a one-day set into two. Book in late winter or spring — crews are booked solid for months after every major outage, exactly when you can't get one.

Fuel burn is the number to plan around. Generac's consumption data puts a 22 kW unit at roughly 2.5 gallons of propane per hour at half load — so a 500-gal tank is only about 3 days of continuous whole-home running — and roughly 210 cubic feet of natural gas per hour, a volume that shows up on your next utility bill. HomeGuide pegs running costs at $30–$170 per day depending on size, load and fuel, with natural gas the cheapest and propane roughly half again per kWh. Budget for upkeep too: an annual service contract runs $200–$650/year, covering oil, filters, battery checks and the exercise-cycle inspections the warranty requires.

Electric service upgrades (a 100→200 A panel is $3,000–$5,000 — see our electrical panel calculator), rock excavation or directional boring, landscaping and hardscape restoration after trenching, propane tank rental, fuel itself, and utility-side gas-meter upgrades the gas company may require for bigger units. Placement matters too: units need roughly 5 ft of clearance from doors, windows and vents for carbon-monoxide safety and run at 60–70 dB — about a vacuum cleaner — so HOAs and setbacks often dictate the final spot.