THE DEFINITIVE GENERATOR GUIDE · PORTABLE
Portable generators. The workhorse.
The most common backup power tool in the country. How conventional generators work, what separates the types that matter, and the fuel and voltage decisions that determine whether yours runs what you actually need it to run.
How it worksTHE BASICS
What makes it a conventional portable generator
A conventional portable generator is a gasoline or multi-fuel engine directly connected to an alternator. The engine runs at a fixed speed, typically 3,600 RPM for a 60 Hz unit, and the alternator converts that mechanical energy into AC electricity. That electricity feeds outlets on the generator panel, and from there it reaches your appliances through extension cords or a transfer switch.
The word "conventional" distinguishes these from inverter generators, which add an electronic conversion step to produce cleaner, more stable power. A conventional generator produces power directly from the alternator. The output is usable for most household appliances, tools, and lights, but it is rougher than what comes out of a wall outlet. Sensitive electronics (laptops, some medical devices, some variable-speed appliances) do better on an inverter generator or behind a quality surge protector.
Because the engine runs at a fixed speed regardless of load, conventional generators burn roughly the same fuel whether powering a single light or a full refrigerator. This makes them less fuel-efficient than inverter generators at light loads, but they compensate with higher maximum output and lower purchase cost. A conventional portable generator delivering 7,500 running watts costs what a 3,000-watt inverter generator costs.
Conventional vs. inverter: not a quality judgment
Neither type is universally better. A conventional generator is the right tool when you need high wattage, 120/240-volt output for a transfer switch, or the lowest cost per watt. An inverter generator is the right tool when you need quiet operation, clean power for electronics, or fuel efficiency at light loads. Many prepared households own both. The generator hub covers the decision between all three types.
CONSTRUCTION TYPES
Six builds, one technology
Every machine below is a conventional generator. They differ in how the engine and alternator are packaged, moved, and powered.
Open-frame generators
The familiar steel-tube-frame machines. Engine and alternator are exposed. They offer the most watts per dollar, strong motor-starting surge capacity, and 120/240-volt output on larger models. The trade-off is noise: an open-frame generator at full load is 72 to 80+ decibels, roughly the volume of a vacuum cleaner to a garbage disposal. They are the right choice when wattage matters more than quiet.
Typical range: 2,000 to 15,000+ running watts. $300 to $2,000.
Wheeled cabinet generators
A step between open-frame and fully enclosed inverter designs. These have partial or full enclosures with wheels and folding handles. Somewhat quieter than open-frame, easier to move, and often positioned as "home backup" models. Many include electric start. The enclosure adds weight and cost but reduces noise by a few decibels.
Typical range: 3,500 to 10,000 running watts. $500 to $1,500.
PTO generators
A power-take-off generator is driven by a tractor PTO shaft instead of its own engine. No engine to buy, maintain, or fuel separately. The tractor provides the mechanical power and the PTO generator converts it to electricity. These can deliver 15,000 to 50,000+ watts depending on tractor size. They require a correctly sized tractor running at the correct PTO speed (typically 540 RPM for residential/farm models). The tractor must remain running and attended while the generator operates.
Best for: farms and homesteads with a reliable tractor already on the property. $1,500 to $5,000 for the generator head.
Jobsite generators
Built for rough handling, intermittent high-demand equipment, and outdoor conditions. These are typically open-frame conventional units with GFCI-protected outlets, reinforced frames, multiple receptacle types, and high surge capacity. They are designed for tools, compressors, and pumps rather than household electronics. For home backup they work, but they are loud and often lack the convenience features (electric start, fuel gauge, low-oil shutoff) found on home-oriented models.
Typical range: 3,000 to 12,000+ running watts. $400 to $2,500.
Towable generators
Trailer-mounted generator sets intended for construction, events, farms, and commercial backup. They are technically portable in that they can be moved, but they are not hand-movable. Diesel, gasoline, propane, or natural gas. Sound-attenuated enclosures. Substantially higher capacity, durability, and cost than any hand-portable unit. Most households do not need one, but a large farm or small business might.
Typical range: 10,000 to 100,000+ watts. $3,000 to $30,000+.
Welder-generators
Combines a generator with an engine-driven welding power source. Produces both welding current and auxiliary AC power from the same engine. Useful for a farm or shop that needs both, but it is a specialized tool. Heavier, more expensive, and more complex to maintain than a standard portable generator. If you do not weld, this is not the right backup power choice.
Typical range: 5,000 to 12,000+ auxiliary watts. $1,500 to $5,000+.
FUEL OPTIONS
Gasoline, propane, or both
Fuel type is a separate decision from generator type. A conventional portable generator can be gasoline-only, dual-fuel (gasoline and propane), or tri-fuel (gasoline, propane, and natural gas). The fuel decision shapes how the generator fits your preparedness plan more than almost any other specification.
Gasoline-only
The simplest and often least expensive option. Gasoline is available everywhere and produces the generator's full rated output. The limitation is storage: untreated gasoline degrades in 30 days and can gum a carburetor within 60. With fuel stabilizer, treated gasoline stays usable for 12 to 24 months. Local fire codes typically limit residential gasoline storage to 25 gallons. After a major storm, gas stations lose power and run dry, which is exactly when you need fuel most.
Dual-fuel (gasoline + propane)
The most resilient portable configuration for most households. Gasoline gives you full rated output and is available at any gas station. Propane stores indefinitely in sealed cylinders without degradation, making it the better long-term storage fuel. Having both options means one fuel source running out or becoming unavailable does not leave you without power.
Propane output is typically 10 to 15 percent lower than gasoline output on the same unit. A generator rated at 7,500 running watts on gasoline may deliver 6,500 to 6,750 watts on propane. This reduction is normal and must be accounted for in load planning. The cost premium for dual-fuel is typically $50 to $150 over a gasoline-only model in the same wattage class.
Tri-fuel (gasoline + propane + natural gas)
Adds natural gas for homes with an active utility gas connection. While the gas line remains live, a tri-fuel generator can run indefinitely without refueling. Natural gas output is typically 15 to 25 percent lower than gasoline. The limitation is dependency: if the gas utility fails during the same event that took the power, the natural gas option is unavailable and you fall back to gasoline or propane. Tri-fuel models cost $100 to $300 more than comparable dual-fuel units.
Diesel (commercial and specialty)
Diesel portable generators are durable and fuel-efficient under steady heavy loads, but they are uncommon among small consumer units. They tend to be heavier, louder, more expensive, and harder to find in the residential wattage range. Diesel is more common in towable generators and commercial applications. For most household backup, gasoline or dual-fuel is the practical choice.
Bottom line on fuel
If you are buying one portable generator for household preparedness, dual-fuel is the recommendation. The small cost premium buys fuel flexibility that matters exactly when you need it most. Store propane for long-term readiness, gasoline for maximum output, and rotate both on a schedule.
THE VOLTAGE QUESTION
120-volt or 120/240-volt. This matters.
This is the specification most first-time buyers overlook, and it determines whether the generator can run your most critical loads. There are two classes of portable generator output, and they are not interchangeable.
120-volt-only
Produces standard household 120-volt power. Works for refrigerators, freezers, lights, chargers, routers, fans, most power tools, small window air conditioners, and anything you plug into a normal wall outlet.
Cannot run a 240-volt well pump. Cannot run central air conditioning. Cannot run an electric range or dryer. Cannot feed a standard whole-house transfer switch, which requires 240-volt input.
If your household has city water and no 240-volt loads, 120-volt-only may be sufficient.
120/240-volt split-phase
Produces both 120-volt branch circuit power and true 240-volt split-phase power. This is the class you need if your household has any of the following: a 240-volt well pump, a 240-volt sump pump, a transfer switch or generator inlet, a shop air compressor, or any other 240-volt equipment.
Do not assume that a high-wattage generator has 240-volt output. Check the specifications explicitly. Look for "120/240V," "split phase," or a 240-volt receptacle (L14-30 or 14-50) on the outlet panel.
If you have a well, you almost certainly need this class.
The well pump question
Whether you need a 120/240-volt generator usually comes down to whether you have a well. Most submersible well pumps are 240-volt. Some shallow-well jet pumps are 120-volt. Check your well pump's nameplate or breaker before buying a generator. If it is on a double-pole (240-volt) breaker, you need a 120/240-volt generator and a transfer switch. No amount of wattage on a 120-volt-only generator will run a 240-volt pump.
REALISTIC LOAD PLANNING
What a portable generator can actually run
Generator marketing uses peak watts and surge watts to make units look bigger than they are. What matters is running watts: the continuous output the generator can sustain while everything you need is operating at the same time. Motor-driven equipment (refrigerators, freezers, pumps, air conditioners) also draws a brief startup surge that can be two to three times the running wattage.
Here are common household loads with their approximate running and starting watts. These are reference estimates. Your equipment may differ. Check nameplates.
| Appliance | Running watts | Starting watts |
|---|---|---|
| Refrigerator | 100 to 400 | 800 to 1,200 |
| Chest freezer | 50 to 100 | 500 to 1,000 |
| Furnace blower (1/3 HP) | 700 to 800 | 1,400 to 2,400 |
| Sump pump (1/3 HP) | 800 | 1,300 to 2,200 |
| Well pump (1/2 HP, 240V) | 1,000 | 2,000 to 3,000 |
| Window AC (5,000 BTU) | 500 | 1,000 to 1,500 |
| Lights, phones, router, laptop | 200 to 400 | Same |
| Microwave (1,000W) | 1,000 | Same |
| Space heater (1,500W) | 1,500 | Same |
| Central AC (3-ton) | 3,500 to 4,000 | 6,000 to 8,000 |
Not everything runs at once. Size the generator for the simultaneous running total plus the largest single startup surge. A household running a refrigerator, freezer, furnace blower, sump pump, and lights simultaneously needs roughly 2,000 to 2,500 running watts, but the furnace blower starting while the sump pump is already running could create a momentary demand of 4,000 to 5,000 watts.
Work it out precisely
The table above gives reference ranges. Your household has specific equipment with specific nameplate ratings. The calculator walks through every load, accounts for startup surges, and gives you a number you can trust.
Open the Power Needs CalculatorCONNECTING TO YOUR HOUSE
Three ways to get power inside
Extension cords
The simplest method. Run outdoor-rated extension cords from the generator's outlets directly to individual appliances. No electrician, no wiring changes. The generator sits outdoors, the cords come through a cracked window or door (stuff towels around the gap, never pinch the cord in a closed door or window), and each appliance plugs in individually.
Limitations: you cannot run your furnace blower, well pump, or hardwired sump pump this way because they are wired into the house panel. Extension cords are limited by their wire gauge: a 12-gauge cord can safely carry 20 amps over short runs, but a long undersized cord creates a voltage drop that can damage motors. Use the shortest cord that reaches. Never daisy-chain cords.
Generator inlet and interlock
A generator inlet is a weatherproof male plug installed on the outside of the house, hardwired into the main panel. A panel interlock is a mechanical device that physically prevents the main breaker and the generator breaker from being on at the same time, ensuring the house is disconnected from the grid before generator power flows in.
This is the most common middle-ground setup: less expensive than a full transfer switch, but it lets the generator feed selected circuits through the house panel. Must be installed by a licensed electrician. $200 to $600 including labor. Requires a 120/240-volt generator with the correct outlet to match the inlet.
Manual transfer switch
A dedicated panel (usually 6 to 10 circuits) installed beside or near your main panel. Each circuit has a switch that toggles between utility power and generator power. When the grid goes down, you start the generator, plug the cord into the inlet, and flip the switches for the circuits you want to power: refrigerator, furnace, well pump, lights.
Cleaner than an interlock because you choose exactly which circuits get power. $400 to $1,000 including professional installation. This is the right connection method for a household that takes portable generator backup seriously. An automatic transfer switch, which starts the generator and transfers power without any human action, is primarily used with standby generators.
Never backfeed through a wall outlet
A "suicide cord" (a cord with two male plugs) plugged from the generator into a wall outlet sends power backward through your house panel and out into the utility lines. This energizes lines that lineworkers believe are dead. It has killed people. It is illegal everywhere. It is also called backfeeding.
The full safety guide covers backfeed prevention, grounding, and transfer-switch requirements.
Read the Generator Safety GuideLIVING WITH A PORTABLE GENERATOR
The maintenance that keeps it running
A generator that will not start during an emergency is one that was not maintained during normal times. Portable generators are simple engines, but they need regular attention, especially when they spend most of their life sitting in a garage or shed waiting to be needed.
Exercise runs
Run the generator every 30 to 90 days for 20 to 30 minutes under light load. This circulates oil, exercises the carburetor, charges the starting battery (if electric-start), and confirms the unit starts and runs. Connect a load: a lamp, a fan, anything that draws current. Running without load is better than not running at all, but a light load is better practice.
Oil changes
Change the oil after the first 20 to 25 hours of operation (break-in period), then every 50 to 100 hours or annually, whichever comes first. Use the oil grade specified in the owner's manual (usually SAE 10W-30 for moderate climates). Check the oil level before every use. Running a generator low on oil can destroy the engine in minutes. Most modern units have a low-oil shutoff sensor, but do not rely on it as your only check.
Fuel management
Gasoline degrades. If the generator will sit longer than 30 days without running, either drain the carburetor and fuel system or add fuel stabilizer to the tank and run the engine for a few minutes to circulate treated fuel through the carburetor. Stale fuel is the single most common reason a generator will not start when needed.
Dual-fuel generators offer a partial solution: store propane for long-term readiness (propane does not degrade in sealed cylinders) and keep gasoline treated and rotated for maximum-output use.
Air filter and spark plug
Check the air filter every 50 hours or annually. Clean or replace it according to the manual. Replace the spark plug annually or every 100 hours. These are inexpensive parts that have an outsized effect on starting reliability and fuel efficiency. Keep a spare spark plug and air filter with the generator.
Storage
Store the generator in a dry, ventilated space (garage, shed, covered outdoor area) out of direct weather. Never store it with fuel in the carburetor bowl for more than 30 days without stabilizer. Cover it to keep dust and moisture out. Keep the starting battery on a trickle charger or battery tender if it has electric start. Store fuel containers separately from the generator, away from ignition sources.
THE RIGHT TOOL
When a portable generator is not the answer
A conventional portable generator is the right tool for many situations, but not all. Knowing when to look at a different category saves money and avoids frustration.
If noise matters: inverter generator
An inverter generator at half load runs at 50 to 60 dB, roughly conversation level. A conventional generator at half load runs at 70 to 80 dB. If you live in a dense neighborhood, have noise-sensitive family members, or plan to sleep while the generator runs, an inverter is worth the higher cost per watt. Inverters also produce cleaner power for sensitive electronics and throttle engine speed to match load, saving fuel.
If you cannot be without power: standby generator
A portable generator requires you to be home, go outside, start it manually, and manage connections and fuel. A standby generator detects the outage and starts automatically within seconds, whether you are home or not. If someone in the household depends on powered medical equipment, if outages are frequent and multi-day, or if the household cannot tolerate any gap in electricity, a standby system is the right investment.
If the loads are small: battery power station
If your critical loads are a CPAP, a phone charger, a router, lights, and a laptop, a battery power station may handle a two-day outage without fuel, noise, or CO risk. Battery stations are the only backup power option safe for indoor use. They pair well with a generator for longer outages: the generator charges the station, the station carries overnight loads quietly.
Every fuel-burning generator produces carbon monoxide
Gasoline, propane, natural gas, diesel. All combustion generators produce CO. Operate outdoors only, at least 20 feet from any door, window, or vent, with exhaust pointed away from the house. Never in a garage, shed, carport, or enclosed porch. Install CO alarms on every level of the home.
Full generator safety guideCONTINUE READING
More from the generator guide.
Generator Guide Hub
Compare all three generator types and find the right starting point for your household.
Portable Power Stations
The quiet, indoor-safe companion that pairs with a generator for shift-running during outages.
Power Needs Calculator
Work out your running watts and startup surges from actual equipment, not guesswork.
Ready to compare specific models? The generator buying guide covers what to look for, and the portable generator roundup reviews the models we would actually buy.