Portable Generator Guide: Sizing, Safety, and Setup

Sizing: How Many Watts Do You Need?

Every appliance has two wattage numbers: running watts (continuous draw) and starting watts (the surge when the motor kicks on). Your generator must handle the starting watts of the highest-draw appliance plus the running watts of everything else simultaneously.

Common appliance wattage: refrigerator (120 running / 1,200 starting), sump pump (800 running / 1,300 starting), window AC unit (1,200 running / 1,800 starting), microwave (1,000 running / 1,000 starting), phone charger (25 running), LED lights (10-15 each), box fan (75 running).

Example calculation for a power outage essentials kit: refrigerator (1,200 starting) + sump pump (800 running, started separately) + 5 LED lights (75 running) + 2 phone chargers (50 running) + a box fan (75 running) = 1,200 starting watts peak, 1,200 running watts continuous. A 2,000-watt inverter generator handles this with headroom.

If you want to add a window AC unit, you need 3,500-4,000 watts. If you want to run a well pump, add another 1,500-2,000 starting watts. Large loads push you into the 5,000-7,500 watt range, which means a conventional (non-inverter) generator.

Generator Types

Inverter generators produce clean, stable power (less than 3% total harmonic distortion) safe for electronics. They are quieter (50-65 dB), lighter (35-65 lbs), and more fuel-efficient because the engine speed varies with the load. They cost more per watt. This is the right choice for most homeowners at 2,000-3,500 watts.

Conventional generators produce rougher power (higher harmonic distortion) that is fine for motors and heating elements but can damage sensitive electronics without a surge protector. They are louder (65-80 dB), heavier (80-200+ lbs), and run at a constant engine speed regardless of load. They cost less per watt and are available in higher outputs. The right choice if you need 5,000+ watts.

Dual-fuel generators (gasoline and propane) give you fuel flexibility. Propane stores indefinitely without stabilizer, does not clog carburetors, and is available when gas stations lose power (propane tanks). The output on propane is about 10% less than on gasoline.

Battery-powered generators (power stations) are silent, produce zero emissions, and can charge from solar panels. They are ideal for camping and electronics charging but most models cannot sustain high-draw appliances (refrigerators, pumps) for extended periods. The technology is improving rapidly, but for a multi-day power outage, fuel-based generators are still the practical choice.

Carbon Monoxide Safety (Life-Critical)

Portable generators produce carbon monoxide, an odorless, colorless gas that kills. CO poisoning from generators kills more people during storms than the storms themselves.

Never run a generator indoors. Not in the garage (even with the door open), not in the basement, not in a crawl space, not in a breezeway. The concentration of CO produced by a generator exceeds lethal levels in minutes.

Place the generator at least 20 feet from any door, window, or vent. Point the exhaust away from the house. Wind can push CO into the house through gaps you did not know existed.

Install battery-powered CO detectors on every level of your home and near sleeping areas. Test them before storm season. Replace batteries annually.

Modern generators have CO-safety shutoff features (required by new CPSC regulations). The generator automatically shuts down if CO levels at the unit reach dangerous concentrations. This is a backup safety feature, not a license to run the unit closer to the house.

If anyone in the house develops headache, dizziness, nausea, or confusion during generator operation, get everyone outside immediately and call 911. Open doors and windows. Do not re-enter until emergency responders clear the space.

Connecting to Your Home

The simplest method: run extension cords from the generator directly to appliances. Use outdoor-rated, heavy-gauge cords (12-gauge for runs up to 100 feet, 10-gauge for longer runs). Do not daisy-chain extension cords. Each appliance gets its own cord from the generator.

A manual transfer switch ($200-500, installed by an electrician) is the proper method for connecting a generator to your home's electrical panel. The switch isolates your home from the utility grid (preventing backfeed that can electrocute line workers) and lets you power specific circuits from the generator. Flipping the switch connects the generator to those circuits; flipping it back reconnects to the grid.

Never plug a generator into a wall outlet (called backfeeding). This bypasses the main breaker and sends power back into the utility lines. It kills utility workers who are repairing the downed power lines. It also fries your generator when the grid comes back on. Backfeeding is illegal in all jurisdictions.

An interlock kit is a simpler alternative to a full transfer switch. It mounts on your existing breaker panel and uses a mechanical interlock that prevents the main breaker and the generator breaker from being on simultaneously. It is cheaper than a transfer switch but still requires an electrician to install.

Fuel Storage and Maintenance

Store gasoline in approved containers (red, UL-listed, no more than 5 gallons each). Keep containers in a ventilated area away from the house, away from ignition sources, and off concrete that can degrade the container.

Add fuel stabilizer (Sta-Bil or equivalent) to stored gasoline. Untreated gas degrades in 30-60 days and leaves gum deposits that clog the carburetor. Stabilized gas lasts 12-24 months. Rotate your fuel stock by using it in your car or lawn mower and refilling.

A 2,000-watt inverter generator uses about 0.5-1 gallon per hour at 25-50% load. Store enough fuel for your expected outage duration. For a 2-day outage running 8 hours per day: 8-16 gallons. For a 5-day outage: 20-40 gallons.

Run the generator dry before long-term storage, or add stabilizer and run it for 5 minutes to circulate treated fuel through the carburetor. Change the oil annually or every 100 hours of operation, whichever comes first.

Test the generator monthly by running it for 15-20 minutes under load (plug something in). A generator that has not been started in 6 months may not start when you need it. Carburetors gum up, batteries die, and fuel goes stale.

Frequently Asked Questions