Buyer's Guide
Running watts, fuel types, the carbon monoxide line you never cross, and how to size a generator to your household.
Reviewed August 2026. We re-check this guide quarterly.
The power goes out and your refrigerator starts warming, your sump pump stops, and the house goes dark. A portable generator can keep the critical circuits running until the grid comes back. But a generator burns fuel, produces exhaust, and delivers raw electrical power that can damage equipment or injure people if handled carelessly. The stakes are higher than with a battery station, and the choices require more homework.
This guide walks you through that homework: what the numbers on the label actually mean, why carbon monoxide is the single most important safety consideration, how the fuel types compare, how to size a unit for your household, and what to look for in the certifications. By the end, you will know what you need before you look at a single product.
Before you buy
Before looking at any generator, answer these about your own situation. They determine the size, fuel type, and features you actually need.
What do you need to keep running?
List the appliances you cannot do without: refrigerator, freezer, sump pump, well pump, furnace blower, medical device. Write down each one's running watts and starting watts from the nameplate or manual. Add them up. This total is the number that sizes your generator.
How will you connect it to your house?
Extension cords from the generator to individual appliances are the simplest path. Powering circuits through your electrical panel requires a transfer switch installed by a licensed electrician. Decide which path before you buy, because it affects the outlets and features you need on the generator.
Where will you run it?
Outdoors only, at least 20 feet from the house, with exhaust pointed away from every window, door, and vent. If you do not have a location that meets those requirements, a generator is not the right solution for your household. A battery power station, which produces no exhaust, may be a better fit.
What fuel can you store and access?
Gasoline is the most available fuel but has the shortest storage life and the highest handling risk. Propane stores indefinitely in a sealed tank. Dual-fuel generators accept both and let you start on whichever you have. Consider what fuel sources will remain accessible to you during the kind of outage you are preparing for.
Do you need clean power for electronics?
Standard open-frame generators produce power with more electrical noise than the grid. An inverter generator produces a cleaner waveform suitable for sensitive electronics like computers and medical devices, but costs more per watt. If your load is mainly lights, a refrigerator, and a pump, a conventional generator is fine.
Guided Finder
Answer a few quick questions about your household and we will point you to the right section of this guide.
The Basics
A portable generator is an engine connected to an alternator. The engine burns fuel, spins a shaft, and the alternator converts that mechanical rotation into electrical current. The electricity flows through outlets on the generator's control panel, and from there to your appliances through extension cords or, with a transfer switch, through your home's wiring.
The engine is the critical difference between a generator and a battery power station. A battery station stores electricity in a lithium battery and releases it silently, with no combustion and no exhaust. A generator creates electricity on demand by burning fuel, which means it produces heat, noise, vibration, and carbon monoxide. Those byproducts are what make the safety rules for generators so much stricter than for battery stations.
The trade-off is runtime. A battery station holds a fixed amount of energy and is empty when it is empty. A generator runs as long as you can feed it fuel. For an outage that lasts days rather than hours, or for loads heavy enough to drain a battery station in a few hours, a fuel generator is the tool that keeps going.
Safety
The most important thing in this guide
Carbon monoxide from a portable generator can kill in minutes. It is colorless and odorless. Victims often lose consciousness before they recognize symptoms. Everything else in this guide is a purchasing decision. This section is not.[1]
The Consumer Product Safety Commission is unambiguous: a portable generator must never be operated inside a home, garage, basement, crawlspace, shed, or any other enclosed or partially enclosed space, even with doors and windows open. Generators produce lethal levels of carbon monoxide, and opening doors and windows does not provide enough ventilation to prevent a fatal buildup.[1]
CPSC data show that an average of nearly 100 people in the United States die each year from carbon monoxide poisoning caused by portable generators.[1] The CDC describes carbon monoxide as a poison that kills without warning and notes that symptoms include headache, dizziness, weakness, nausea, and confusion, which are often mistaken for the flu.[4]
Operate the generator outdoors only, at least 20 feet from the house, with the exhaust pointed away from all windows, doors, and vents. Not on a porch. Not in a carport. Not in a garage with the door open.[1] The CDC recommends the same distance and warns against using generators, grills, camp stoves, or any gasoline- or charcoal-burning device inside a home, basement, or garage, or near a window.[5]
Install battery-operated or battery-backup carbon monoxide alarms on every level of the home and outside each sleeping area. Interconnected alarms are best: when one sounds, they all sound. Test alarms monthly. When a CO alarm sounds, get outside immediately and call 911.[1]
If your household cannot meet the 20-foot outdoor-placement requirement, a generator is not the right backup power solution. A portable power station has no engine and produces no carbon monoxide, and it can run safely inside the home. The companion handbook covers that option in full.
Specifications
Every generator lists two wattage numbers. Running watts (also called rated watts) is the continuous output the generator can sustain. Starting watts (also called surge watts or peak watts) is a brief burst of extra power available for a few seconds to start motor-driven appliances. Sizing is done against running watts for your total simultaneous load, with starting watts checked against the largest single motor you will start. If you plan to run a 4,800-watt load and your refrigerator has a 1,200-watt starting surge, you need at least 4,800 running watts and at least 6,000 starting watts.
Manufacturers list runtime at half load and sometimes at rated (full) load. Half-load runtime is always the bigger, more marketable number. At rated load, runtime is roughly half of the half-load figure because the engine is working harder and consuming fuel faster. Plan your fuel supply against the rated-load number for the first day, then adjust downward once you know your actual draw.
Most portable generators provide a combination of standard 120V 20A duplex outlets, one or two 120V 30A twist-lock outlets, and possibly a 120/240V 30A or 50A outlet for a transfer switch connection. Match the outlets to your connection plan. If you will use a transfer switch, confirm the generator has a twist-lock outlet that matches your switch's inlet.
Total harmonic distortion (THD) measures how clean the electrical output is. Standard open-frame generators produce power in the 10 to 25 percent THD range, which is fine for resistive loads like lights, heaters, and basic appliances. Inverter generators use electronics to produce a cleaner sine wave, typically under 3 percent THD, which is safe for computers, medical devices, and other sensitive electronics. An inverter generator is also significantly quieter and more fuel-efficient at partial loads, but costs more per watt of output.
Certifications
Two voluntary standards address the carbon monoxide hazard in portable generators. Both are worth understanding before you buy.
Published by the Portable Generator Manufacturers' Association. Requires a CO shutoff system that automatically stops the generator when dangerous carbon monoxide concentrations are detected near the unit. Also requires a notification to the user after shutoff. CPSC staff analysis found that compliant generators would avert approximately 87 percent of the CO fatalities in their database.[3]
Published by Underwriters Laboratories. Includes the same CO shutoff requirement as PGMA G300 and adds a reduced CO emission rate requirement, meaning the engine itself produces less carbon monoxide per unit of fuel consumed. CPSC staff analysis found that compliant generators would avert nearly 100 percent of the CO fatalities.[3] UL 2201 also covers rainproof enclosures, weather-resistant receptacles, and ground-fault circuit interrupters on 120V AC output circuits.
The CPSC recommends looking for generators certified to one of these standards and specifically notes that UL 2201 certified models have reduced CO emissions in addition to the shutoff feature.[1] A mandatory federal safety standard incorporating elements of both was proposed in 2023 and was still in the rulemaking process as of the date of this guide.
Fuel
| Fuel | Storage life | Output | Storage safety |
|---|---|---|---|
| Gasoline | 3 to 6 months (with stabilizer, up to 12) | Full rated watts | Highest handling risk. Flammable vapors. Store in approved containers outside living areas. |
| Propane (LP) | Indefinite in a sealed tank | About 10% fewer watts than gasoline on the same engine | Lower handling risk. No degradation. Stored in sealed tanks. |
| Natural gas | Continuous supply if utility line is intact | About 10 to 15% fewer watts than gasoline | No storage needed. Supply depends on the gas utility staying operational. |
Dual-fuel generators accept both gasoline and propane, giving the household a choice at the moment of need. Some tri-fuel models add natural gas. Having two fuel options means a gasoline shortage during a regional outage does not leave the generator useless.
The CPSC warns that gasoline, propane, kerosene, and other flammable liquids should be stored outside of living areas in properly labeled, non-glass safety containers. They should never be stored near a fuel-burning appliance such as a natural gas water heater, because invisible vapors from a spill or a loose seal can travel along the ground and be ignited by a pilot light.[2]
Before refueling, turn off the generator and let it cool. Gasoline spilled on hot engine parts can ignite.[2] Never refuel a running generator.[6]
Sizing
Sizing a generator is arithmetic, not guesswork. The steps are straightforward, and getting them right saves you from buying too large (wasting money and fuel) or too small (overloading the generator and potentially damaging your appliances).
Write down every appliance you need to run during an outage. For each, find the running watts from the nameplate, manual, or manufacturer's website. Common household loads:
| Appliance | Typical running watts | Typical starting watts |
|---|---|---|
| Refrigerator | 150 to 400 | 800 to 1,200 |
| Chest freezer | 50 to 100 | 500 to 1,000 |
| Sump pump (1/3 HP) | 800 | 1,300 to 2,000 |
| Well pump (1/2 HP) | 1,000 | 2,000 to 3,000 |
| Furnace blower | 500 to 800 | 1,000 to 2,350 |
| Window AC (10,000 BTU) | 1,200 | 1,800 to 3,600 |
| Lights (10 LED bulbs) | 100 | 100 |
| Phone and laptop chargers | 50 to 100 | 50 to 100 |
Total the running watts of everything you plan to power simultaneously. This is the minimum running-watt rating your generator needs. Add a buffer of roughly 20 percent for safety margin and for loads you may have forgotten.
Find the single appliance with the highest starting watts. Add that number to your running-watts total (minus the appliance's own running watts, since the surge replaces the running draw during startup). The generator's starting-watt rating must be at least this high. Start motor-driven appliances one at a time to avoid stacking surges.
| Running watts | Typical household fit |
|---|---|
| 2,000 to 3,500 | Essentials only: refrigerator, lights, phone charging, one small appliance at a time |
| 3,500 to 5,500 | Essentials plus a sump pump or furnace blower. Covers most moderate household outage plans |
| 5,500 to 7,500 | Multiple circuits including a well pump, window AC, or a small workshop load |
| 7,500 to 12,000+ | Near-whole-house coverage through a transfer switch. Central AC may be possible at the higher end |
The power needs calculator on the energy section can help you add up your specific loads.
Comparison
These are not competing products. They solve different problems, and many households benefit from having both.
| Fuel generator | Battery station | |
|---|---|---|
| Carbon monoxide | Yes. Outdoor use only, 20 feet from the house. | None. Safe indoors. |
| Runtime | Unlimited with fuel supply. | Fixed by battery capacity. Empty when empty. |
| Noise | Noticeable to loud (50 to 75 dB typical). Inverter models are quieter. | Near silent. |
| Best for | Multi-day outages, heavy loads (well pump, central circuits), extended runtime needs. | Short outages, indoor use, quiet overnight power, medical devices, sensitive electronics. |
| Maintenance | Oil changes, fuel stabilizer, periodic run-ups, spark plug replacement. | Minimal. Keep charged to 50 to 80 percent when stored. |
A common pairing is a generator for the heavy daytime loads and a battery station for quiet overnight power and indoor convenience. The portable power stations handbook covers the battery side in full.
What Goes Wrong
Unstabilized gasoline degrades in as little as three months. Gummed-up carburetors are the most common reason a generator will not start when you need it. Run the generator monthly for 15 to 30 minutes under load, use fuel stabilizer in stored gasoline, and either drain the carburetor before long storage or run it dry.
Connecting more load than the generator's running-watt rating causes voltage sag, overheating, and breaker trips. Start motor-driven appliances one at a time to avoid stacking surge loads. If lights dim or the engine surges, reduce load immediately.
Plugging a generator into a wall outlet to power the house wiring without a transfer switch sends electricity back into the utility lines. This creates a lethal electrocution hazard for utility workers and neighbors served by the same transformer. The CPSC warns against backfeeding, and the practice is prohibited by the National Electrical Code.
A generator running in rain or standing water creates a shock hazard. Operate on a dry surface under a canopy or purpose-built cover that does not enclose the unit or restrict airflow. Never touch a generator with wet hands. Use GFCI-protected outlets or portable GFCI adapters.
Running a generator with low or old oil seizes the engine. Check oil before every use. Change oil after the first 20 hours and every 50 to 100 hours thereafter, or per the manufacturer's schedule.
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After You Buy
A generator that sits in the garage untouched for three years will not start on the night you need it. Ownership means maintenance, practice, and keeping the fuel fresh.
Monthly run-up: Start the generator, let it warm up, and run it under a moderate load (a space heater or a shop light) for 15 to 30 minutes. This circulates oil, keeps the carburetor clear, and confirms it works.
Oil changes: Follow the manufacturer's schedule. Fresh oil is the cheapest insurance against a seized engine.
Fuel rotation: Use stabilized gasoline and rotate it every six months. Or keep propane as your primary fuel and avoid the degradation issue entirely.
Extension cords: Use outdoor-rated, heavy-gauge cords. A cord too light for the load overheats and creates a fire hazard. Match the cord's amperage rating to the circuit.
Learn more: The generators guide in the energy section covers setup, maintenance, and safe operation in more detail.
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