Whole House Generator Cost Guide 2026: Install + Operating Costs by Size

A whole house generator is the most expensive backup option most homeowners ever buy, and the sticker price is the smallest number in the decision. This guide separates the three real costs: what the box costs (verified dealer prices, dated this week), what the install costs (survey bands, not guesses), and what it costs to run (a natural gas vs propane table computed from October 2026 EIA prices and Generac's published burn rates). Where a number is not verified, we say so instead of inventing it.

What a whole house generator costs, by size

Two prices matter and they are not the same price. The unit-only prices below are live dealer listings dated 2026-10-15, and they show what the box itself costs; the installed bands come from 2026 cost surveys recorded in our generators dataset. Most homeowners land at $10,000-$15,000 all-in for an 18-22kW unit, and Generac complete-install packages span $8,000-$25,000 depending on site work.

What drives the install cost

The gap between a $6,129 box and a $10,000-$15,000 project is labor and parts that the box does not contain. Four line items do most of the work, and only the first has a verified price story:

• The transfer switch. This is the pricing trap: some listings include it, most do not. The verified contrast is on this page: Briggs & Stratton's $8,069 PowerProtect 40816 listing includes a 200A ATS, while the Generac 7042 and Kohler 20RCA listings above are unit only, transfer switch extra. When you compare prices across brands, check what is in the box before you check the number.
• The gas line. A standby burns natural gas or propane vapor, and connecting it to your meter or tank is plumbing work whose cost scales with how far the generator sits from the fuel source. We have no verified per-foot number, so we print none; it belongs in the installer's quote.
• The pad and placement. The unit sits on a concrete or composite pad outside, at code-required clearances from windows and openings. Site prep varies per house; no universal number exists.
• Permits and inspections. Electrical and fuel permits with local fees that vary by jurisdiction; see the FAQ below.

The honest summary: the unit is a commodity with a visible price, the install is a construction project with a quote. That is why the all-in bands are wide, and why two bids on the same unit can differ by thousands without either being wrong.

Natural gas vs propane: what it costs to run

Fuel is the recurring cost nobody prices before buying, so here is the whole computation, shown so you can rerun it. Burn rates are the Generac 7042 Guardian 22kW spec-sheet figures (Generac published specs via gescan.com, verified 2026-10-15): 310 ft³/h of natural gas at 100% load and 216 ft³/h at 50% load; 140 ft³/h of propane vapor at 100% and 93.2 ft³/h at 50%.

The formulas, on the record:

• Natural gas: $/hr = (ft³/h ÷ 1,000) × $/Mcf
• Propane: $/hr = (ft³/h ÷ 36.39) × $/gal, because one gallon of propane is about 36.39 ft³ of vapor (EIA energy units calculator)

Prices are EIA, current as of this guide: residential natural gas at $26.45 per thousand cubic feet (July 2026 monthly, series N3010US3, release 9/30/2026) and residential propane at $2.638/gallon (week of 10/12/2026, EIA weekly heating oil and propane release, 10/15/2026).

Generac vs Kohler vs Briggs & Stratton

The three brands that will end up on your bid sheet, on this week's verified dealer prices. Strengths stay qualitative because the differences that matter are dealer coverage, support, and the surrounding product line, not spec-sheet lines we cannot verify.

How many kW do you need?

Sizing is where money is wasted in both directions: too small and the breaker trips when the AC kicks in, too large and you paid for kilowatts that never run. Two scenarios cover most houses:

The central AC is the whole game in scenario two: a compressor's starting surge is the largest single load a house presents, with typical residential surge up to 12,000W. A soft-start kit at $100-$350 cuts the air conditioner's starting watts by 60-70%, which is often the difference between an 18kW unit and a 26kW one. Spend the kit money before you spend the size money.

The portable alternative: a transfer switch and a good inverter

Not every house needs a standby. If your essentials are fridge, lights, internet, and devices, a 2000W-class portable inverter plus a transfer solution does the job for a fraction of the installed cost. The verified anchor: the Honda EU2200i tracks at $1,199-$1,347.99 across 7 live offers (generatorbible.com, 2026-09-14). The Generac GP2200i and Champion 201230 are the other two picks in our portable coverage; their street prices are not verified this run, so we print no numbers for them.

The catch, plainly: a portable does not start itself, most cannot start a central AC, and it must live outdoors at least 20 feet from the house because of carbon monoxide, exactly like any engine. Transfer-switch hardware pricing is not verified this run, so budget it from your electrician's quote rather than from us. The full portable-vs-standby decision frame is in Generator vs Power Station vs Solar Generator, and storm-season timing is covered in Hurricane Season 2026 Backup Power.

Standby generator vs battery backup

A generator's fuel arrives by pipe and runs indefinitely; a battery is silent, indoor-safe, and flat when it is flat. If your outages are short and your loads are modest, a home battery starts at a very different price point and doubles as a solar energy asset: the full portable-vs-installed split is our Home Battery Backup Guide, and the economics live in the Battery Storage ROI Analyzer.

Cost FAQ

The one-sentence version: budget the box from the dated dealer prices above, budget the project from the $10,000-$15,000 all-in band, and budget the fuel from the EIA-priced table before you sign anything.