The number that matters: honest running watts on the fuel you'll actually use
Ignore the kW badge on the box. A "24kW" standby unit is 24kW on propane — on natural gas, the fuel almost every permanent install runs on, its honest continuous output is lower (the 24kW Guardian is really ~21,000 running watts on NG). That's the number the tool ranks by, because it's what actually powers your house. Rough sizing: a 2,000 sq ft home on essentials runs on ~10–14kW; a 3,000+ sq ft home wanting AC, well pump and range wants 18–24kW. Matching a 200-amp service whole-house switch typically means a 20kW+ unit with a service-rated ATS.
What about installation cost?
Sticker price is only half the story — a permanent standby needs a gas line, a pad, a transfer switch and a licensed electrician/plumber, often $3,000–$6,000+ on top of the unit. That's why the tool weights Includes ATS separately (a bundled automatic transfer switch saves a real line-item) and why portables — which need no install but need you to roll them out and run cords — sit in their own filter. Use the type filter to compare within an install class so you're not pricing a plug-and-play portable against a professionally-installed standby.
Standby vs portable vs battery vs solar
Standby = automatic, whole-house, utility-gas-fed (runtime is effectively unlimited), but $$$ installed and ~60–68 dB running. Portable = cheapest upfront and movable, but manual start, finite tank runtime (8–11 hr at half load), louder (~74 dB), and no automatic cutover. Battery backup / solar is silent and emissions-free but capacity-limited for long outages and pricey per kWh — great for short outages and overnight, weak for a multi-day storm that a gas unit shrugs off. This tool ranks the fuel-burning options head-to-head; pick the class that fits your outage profile.
Why we don't just name a winner
"Best generator" depends entirely on your house size, whether you can run gas, how close the neighbors are, and your budget. A big all-electric home cares about running watts + ATS; a townhouse cares about noise; a weekend cabin cares about a cheap portable. One name buries that — the Value Score keeps it in your hands, formula in the open right above. Compare Generac vs Kohler vs Cummins vs Champion vs Briggs by the specs that matter to you.
The specs, briefly
Running watts (NG) = honest continuous output on natural gas — the real whole-house number (lower than the LP kW badge). Fuel flexibility = how many fuels it accepts (dual-fuel NG/LP standby or gas/LP portable = 2). Runtime @ 50% load = hours on a tank for portables; utility-fed standby units run continuously (shown as ∞). Quiet (23ft) = dB(A) measured at 23 ft, lower is better. Warranty = residential limited warranty years. Includes ATS = the automatic transfer switch ships in the base SKU (many base standby SKUs do not — you buy the switch separately).
Specs verified Aug 2026 against manufacturer spec sheets + curated OEM aggregators (BackupAtlas, GeneratorsDatabase, each citing the OEM source). Running watts are continuous output on natural gas for standby / gasoline for portables — deliberately the honest baseline, not the marketing kW/surge number. Prices are approximate street prices for the generator unit only, not installed; permanent standby pro-install adds ~$3k–6k+. Some links may be affiliate; that never changes the Value Score — the math runs on published specs, not payouts.