Portable Generator Guide: Sizing, Safety, and Setup

Sizing: How Many Watts Do You Need?

Every appliance has two wattage numbers: running watts (the continuous draw during normal operation) 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 you plan to operate simultaneously.

Common appliance wattage based on manufacturer specs: 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). These numbers vary by model, so check the nameplate on your specific appliances for exact figures.

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

If you want to add a window AC unit, the math changes significantly. The AC unit alone needs 1,800 starting watts, which pushes the total requirement to 3,500-4,000 watts. If you need to run a well pump (common in rural areas where grid power also runs the water supply), add another 1,500-2,000 starting watts. Large loads like these push you into the 5,000-7,500 watt range, which means a conventional (non-inverter) generator and substantially more fuel consumption.

Generator Types

Inverter generators produce clean, stable power with less than 3% total harmonic distortion, which is safe for laptops, phones, and other sensitive electronics. They run quieter (50-65 dB, comparable to a normal conversation), weigh less (35-65 lbs for 2,000-3,500 watt models), and consume less fuel because the engine speed adjusts automatically to match the load. The Honda EU2200i and Yamaha EF2200iS are the benchmarks in this category, priced at $1,000-1,200. The Champion 200986 and WEN 56203i offer similar output at $400-600. Inverter generators cost more per watt but are the right choice for most homeowners at the 2,000-3,500 watt range.

Conventional generators produce rougher power with higher harmonic distortion. This is fine for motors, refrigerators, heating elements, and lights, but can damage sensitive electronics unless you add a surge protector. They are louder (65-80 dB, comparable to a lawn mower), heavier (80-200+ lbs), and run at a constant engine speed regardless of load. Their advantage is lower cost per watt and availability in higher outputs. The Westinghouse WGen5300v and Champion 100519 are popular models in the 5,000-7,500 watt range at $500-900. This is the right choice if you need 5,000+ watts.

Dual-fuel generators (gasoline and propane) offer valuable fuel flexibility. Propane stores indefinitely without fuel stabilizer, does not clog carburetors during long-term storage, and is often available when gas stations lose power during extended outages (you can swap a standard tank at many retailers). The tradeoff is about 10% less output on propane compared to gasoline. Several manufacturers including Champion and DuroMax offer dual-fuel models across the wattage range.

Battery-powered generators (portable power stations from EcoFlow, Bluetti, and Jackery) are silent, produce zero emissions, and can recharge from solar panels. They are excellent for camping, tailgating, and keeping electronics charged during short outages. However, most models under $2,000 cannot sustain high-draw appliances like refrigerators and sump pumps for extended periods. A 2 kWh power station keeps a refrigerator running for roughly 10-15 hours. For a multi-day power outage where you need a sump pump running around the clock, fuel-based generators remain the practical choice.

Carbon Monoxide Safety (Life-Critical)

Portable generators produce carbon monoxide (CO), an odorless, colorless gas that kills. According to the Consumer Product Safety Commission, CO poisoning from portable generators kills more people during major storms than the storms themselves. This section is not cautionary advice. It is a set of rules that prevent death.

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, not in a carport. The concentration of CO produced by even a small generator exceeds lethal levels in an enclosed space within minutes. An open garage door does not provide adequate ventilation.

Place the generator at least 20 feet from any door, window, or vent. Point the exhaust away from the house. Wind direction can shift and push CO into the house through gaps around windows, doors, and dryer vents that you did not know existed. More distance is always better than less.

Install battery-powered CO detectors on every level of your home and near all sleeping areas. Test them before storm season each year. Replace batteries annually and replace the entire unit according to the manufacturer's recommended lifespan (typically 5-7 years). A CO detector costs $20-40 and is the last line of defense if CO infiltrates the house despite proper generator placement.

Modern generators increasingly include CO-safety shutoff features, required by recent CPSC regulations. The generator monitors CO concentration at the unit and automatically shuts down if levels reach dangerous thresholds. Models from Briggs & Stratton, Honda, and Generac include this technology in current production units. This is a backup safety feature, not a reason to place the generator closer to the house than the 20-foot minimum.

If anyone in the house develops a headache, dizziness, nausea, or confusion during generator operation, get everyone outside immediately and call 911. Open doors and windows on your way out. Do not re-enter the home until emergency responders clear the space with CO monitoring equipment.

Connecting to Your Home

The simplest connection method is running extension cords from the generator directly to individual 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 or use indoor-rated cords outdoors. Each appliance should get its own cord from the generator. See our extension cord safety guide for sizing details.

A manual transfer switch ($200-500 for the switch, plus $200-500 for professional installation by a licensed 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 utility line workers. It lets you power specific circuits (refrigerator, sump pump, furnace blower, select lighting) directly from the generator by flipping the transfer switch. When grid power returns, flipping the switch back reconnects to the utility and disconnects the generator.

Never plug a generator into a wall outlet (a practice called backfeeding). This bypasses the main breaker and sends power backward into the utility lines. It kills utility workers who are repairing downed power lines, sometimes miles away from your house. It also destroys your generator when grid power comes back on and the utility feed collides with the generator output. Backfeeding is illegal in all jurisdictions and violates every electrical code.

An interlock kit is a less expensive alternative to a full transfer switch. It mounts on your existing breaker panel and uses a mechanical interlock plate that physically prevents the main breaker and the generator breaker from being in the "on" position at the same time. This achieves the same safety function (preventing backfeed) at a lower cost ($50-150 for the kit, plus electrician installation). The generator connects to a dedicated inlet box on the exterior of the house via a heavy-gauge cord.

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 direct contact with concrete (which can degrade plastic containers over time). A shelf in a detached shed or garage is ideal.

Add fuel stabilizer (Sta-Bil or equivalent) to all stored gasoline. Untreated gas degrades in 30-60 days, leaving gum and varnish deposits that clog the carburetor. Stabilized gas lasts 12-24 months. Rotate your fuel stock by pouring it into your car or lawn mower and refilling the containers with fresh gas every 6-12 months.

Fuel consumption varies by generator size and load. A 2,000-watt inverter generator at 25-50% load uses about 0.5-1 gallon per hour. 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 extended outage: 20-40 gallons. Manufacturer specs for your specific model provide more precise consumption figures at various load levels.

Before long-term storage, either run the generator until the fuel system is dry (start it and let it run until it stalls) or add stabilizer and run the engine for 5 minutes to circulate treated fuel through the carburetor and fuel lines. Change the oil annually or every 100 hours of operation, whichever comes first. Most portable generators use standard 10W-30 motor oil.

Test the generator monthly by running it for 15-20 minutes under load (plug in a lamp or a fan). A generator that has not been started in 6 months may not start when you need it during an emergency. Carburetors gum up, batteries go dead, and fuel goes stale. The time to discover a starting problem is during a monthly test, not during an ice storm at 2 AM.

Frequently Asked Questions

What Size Generator Do I Need for My House?

For power outage essentials (refrigerator, sump pump, lights, phone charging, a fan): a 2,000-watt inverter generator at $400-1,200. For essentials plus a window AC unit or a well pump: 3,500-4,500 watts at $500-1,000. For essentials plus central AC or electric heat: 7,500-10,000+ watts. At that power level, a whole-house standby generator with an automatic transfer switch is often the better long-term investment compared to a massive portable unit.

How Long Can I Run a Generator Continuously?

Most portable generators run 8-12 hours on a full tank at 25-50% load. Inverter generators at light loads can stretch to 10-16 hours per tank. You cannot run a generator 24/7 during a multi-day outage. Plan for 8-12 hour run cycles with breaks for cooling, refueling, and oil level checks. Never refuel a hot generator. Let it cool for at least 10 minutes first. Gasoline splashed on a hot exhaust manifold ignites immediately.

Is a Whole-House Generator Worth the Cost?

A whole-house standby generator ($5,000-15,000 installed, including the automatic transfer switch and gas line) makes sense if you experience frequent or extended outages (multiple times per year or lasting more than 24 hours), have medical equipment that requires continuous power, have a sump pump protecting a finished basement, or live in a climate with extreme heat or cold where losing HVAC creates a health risk. For occasional short outages (a few times per year, lasting 4-12 hours each), a portable generator at $500-1,500 is the practical and cost-effective choice.

Related Reading

• Storm Prep Tool Kit
• Extension Cord Safety
• Home Electrical Safety