How to Choose the Right Size Generator for Your Home

A generator that’s too small leaves your fridge and furnace fighting over watts during an outage. One that’s too big means paying for fuel and capacity you’ll never use. Sizing a generator correctly comes down to simple math: add up the running watts of what you want to power, then account for the extra “starting watts” that motors need for a split second when they kick on.

Step 1: Add up your running watts

Every appliance has a running wattage and, if it has a motor or compressor, a higher starting wattage. A refrigerator might run at 200 watts but spike to 800-1,200 watts for a second when the compressor kicks on. A furnace blower, sump pump, well pump, and window AC unit all behave the same way. Check the nameplate on the appliance or its manual for both numbers, and plan around the highest single starting-watt spike you’ll have running at once, since generators need enough surge capacity to handle that moment even if it only lasts a couple of seconds.

Step 2: Match your watt total to a generator class

• 2,000-3,000 watts — Powers a fridge, some lights, a laptop, and a phone charger. Good for camping or light backup, not a real power outage for a house.
• 7,500-10,000 watts — Covers the “essentials” circuit of a 1,500-2,500 sq ft home: fridge, furnace blower, well pump, sump pump, a few circuits of lights and outlets. This is the sweet spot for most homeowners buying backup power.
• 12,000-13,000+ watts — Can run most of a mid-size house including central air conditioning, without the careful appliance-by-appliance rationing smaller units require.
• Whole-home standby (15,000-48,000+ watts) — Permanently installed, runs on natural gas or propane, and switches on automatically. This is the no-compromise option but costs several times more than a portable unit and requires professional installation.

Step 3: Decide between portable, inverter, and dual-fuel

Portable gas generators in the 7,500-13,000 watt range, like the DuroMax dual-fuel 12,000W, give you the most watts per dollar and can usually run on gasoline or propane. Inverter generators such as the Honda EU2200i produce cleaner, quieter power that’s safe for sensitive electronics, but top out around 2,200-3,000 watts per unit, so you’d need to pair two together for whole-home backup. If you want remote starting and a 30-amp outlet sized for a transfer switch, the Westinghouse WGen7500 is a commonly recommended middle-ground pick. Buyers on a tighter budget frequently look at the Generac GP Series portable generator, which covers the same 7,500-10,000 watt sweet spot at a lower price than premium dual-fuel units, trading away some of the extra features rather than core running capacity.

Step 4: Plan the connection, not just the generator

A generator only helps if you can safely get its power into your house. For whole-panel or multi-circuit backup, you need a transfer switch — ideally installed by a licensed electrician — which prevents dangerous backfeeding into utility lines. If you’re only running a few cord-and-plug appliances (a fridge, a window AC, some lamps), heavy-duty 12-gauge outdoor extension cords rated for the wattage you need are enough, and no electrical work is required. Either way, never run a generator inside a garage or near windows and doors; the CPSC recommends at least 20 feet of clearance from the house with the exhaust pointed away from any opening.

A simple way to double-check your number

Once you’ve added up running watts and identified your single biggest starting-watt spike, add about 20-25% headroom on top of the total. That buffer covers voltage fluctuations and lets you add one more appliance later without overloading the unit. If your math lands you right at the edge of a generator’s rated wattage, size up rather than down — running a generator at its absolute max for hours at a time shortens its lifespan and increases the odds of nuisance shutdowns during the exact outage you bought it for.

Buying Considerations: Fuel Type, Runtime, and Altitude

Fuel type affects both convenience and shelf life — gasoline is the most widely available but degrades within a few months without a stabilizer, propane stores indefinitely and burns cleaner but delivers slightly less power per tank, and dual-fuel units let you switch based on whichever is available during a prolonged outage when gas stations may be without power themselves. Runtime at half load (the number manufacturers usually advertise) is almost always longer than runtime at the full rated wattage, so check both figures if you plan to run the generator near its max capacity for extended stretches, like through an overnight outage. If you live at higher elevation, note that generator output derates with altitude — a unit rated for sea level can lose a meaningful percentage of its output above a few thousand feet, which matters if you’re already sizing close to the edge of your wattage needs.

Frequently Asked Questions

How long can a portable generator run continuously during an extended outage?

Most portable generators are rated for continuous operation as long as fuel and oil levels are maintained, but manufacturers typically recommend a brief cool-down and oil check every 8-12 hours of continuous use, and most units need refueling every 8-10 hours at moderate load.

Is it safe to plug a generator directly into a wall outlet without a transfer switch?

No — this is one of the most dangerous generator mistakes, since it can backfeed electricity into utility lines and seriously injure or kill utility workers, in addition to damaging your generator and home wiring. Always use a transfer switch for whole-panel connections or a properly rated extension cord for individual appliances.

Bottom Line

Size your generator off actual running and starting watts, not a vague sense of “big enough.” Most homeowners land in the 7,500-10,000 watt range for genuine outage coverage, with inverter units reserved for quiet, electronics-safe backup and whole-home standby systems reserved for buyers who want zero manual intervention during an outage.

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