Standby Generator Sizing and Placement Rules

The kilowatt number no cost guide will give you

Cost guides — including this site's own standby generator cost calculator — price a machine once you tell them the kilowatt tier, but none of the published national cost sources behind that pricing publishes an appliance wattage table, and this site does not invent one just to compute a number for you. Sizing a generator correctly means doing that arithmetic yourself, and it is more specific than "how big is my house":

1. List every appliance or circuit you want the generator to run at the same time.
2. Add up their running watts — the steady load once each is already on.
3. Find the single highest starting watts figure among them — the surge a motor draws for a moment when it kicks on, which can run 2 to 6 times its own running watts.
4. Add that appliance's starting watts minus its own running watts to your running-watt total.
5. Multiply the result by 1.20 for a 20% safety margin, then convert to kilowatts.

The starting-watts step is the one homeowners skip and the one that actually breaks an undersized system: a generator can be perfectly adequate for your running load and still stall the instant a motor-driven appliance switches on, because the surge — not the steady load — is what exceeds its capacity. A 3-ton central air conditioner is the example worth knowing by heart: roughly 3,800 running watts, but as much as 8,500 watts the instant the compressor starts. A ⅓-HP sump pump runs about 800 watts and starts around 1,300; a ½-HP furnace blower runs about 800 and starts around 2,350.

As a rough anchor before you run your own numbers: essential circuits alone (refrigerator, lighting, a sump pump, a router) typically land in the 5,000-7,500 watt range, while a true whole-house setup with central AC typically needs 14,000-24,000 watts. Once you have a target kilowatt figure, look up that tier on the standby generator cost calculator to price the machine and the switchgear together.

Where you're actually allowed to put it

Placement is governed by three layers that stack, not substitute for each other: NFPA 37 sets a national baseline, the manufacturer's installation manual can tighten it for a specific model, and your local jurisdiction adds its own permit and noise requirements on top.

Practically, this means the spot a homeowner picks first — tucked close to the house, near a bedroom window, for the shortest possible wiring and gas runs — is often exactly the spot the window clearance rules it out. Settle placement with your installer and your permitting office before you lock in a kilowatt tier and a budget, since moving the unit later can mean re-running wiring and fuel piping that were already priced and installed.