What a generator system does and the main types
A generator system converts fuel or another energy source into electrical power when the grid is down or unavailable. The system includes the generator itself, fuel storage, transfer equipment, and sometimes a battery bank or inverter. Generators fall into three broad categories based on how they're used: portable units you move by hand or cart, standby units that sit outside your home or business, and inverter generators that produce cleaner power for sensitive electronics.
Portable generators are the smallest and cheapest option—they run on gasoline, propane, or diesel and produce 2,000 to 7,500 watts. Standby generators are permanently installed, larger, and typically run on natural gas or propane; they can produce 7,000 to 48,000 watts or more and often start automatically when power fails. Inverter generators are portable but more expensive; they regulate power output to protect laptops, phones, and medical equipment.
The fuel type matters for cost, storage, and convenience. Gasoline is cheap and widely available but degrades in storage and requires frequent refueling during extended outages. Propane stores longer and doesn't degrade, but you need a tank and refill service. Natural gas is convenient if your home already has a line, but you depend on the utility to maintain pressure during an outage.
Key Takeaways
- Portable generators are affordable and movable but require manual refueling and produce more noise; standby generators are permanent, automatic, and quieter but cost significantly more upfront.
- Fuel type—gasoline, propane, or natural gas—affects how long you can run the generator, how often you refuel, and how much fuel costs over time.
- Generator size in watts must match your actual power needs: essential circuits only (5,000–10,000 watts), whole-home backup (15,000–20,000 watts), or larger loads like air conditioning (25,000+ watts).
- Inverter generators cost more but produce stable power safe for computers and medical devices; standard generators are cheaper but can damage sensitive electronics.
- Proper installation, regular maintenance, and safe fuel storage prevent injury, equipment damage, and carbon monoxide poisoning.
Sizing a generator to match what you actually need
The most common mistake is buying a generator too small to run what matters or too large and wasting money. Start by listing the appliances and devices you want to power during an outage: refrigerator, furnace, water heater, lights, phone chargers, medical equipment, or a sump pump. Write down the wattage for each—you'll find it on the device label or in the manual.
Add up the running wattage (the steady power the device uses) for everything you want to run at the same time. Many appliances also have a starting wattage, which is higher than running wattage and lasts only a few seconds when the motor first turns on; a refrigerator might need 600 watts to run but 2,000 watts to start. Your generator must handle the highest starting wattage of any device you'll turn on together, plus the running wattage of everything else.
A modest setup—lights, refrigerator, furnace, and phone chargers—typically needs 5,000 to 10,000 watts. Adding a water heater or well pump pushes you toward 10,000 to 15,000 watts. Running air conditioning or electric heat during an outage usually requires 20,000 to 30,000 watts or more. If you're unsure, an electrician can review your panel and tell you what size makes sense for your home.
Portable generators: cost, noise, and fuel management
Portable generators cost between $500 and $3,000 depending on wattage and fuel type. They're the right choice if you want something you can move between locations, don't want to install anything permanently, or need backup power only occasionally. The trade-off is that you must refuel them manually, they're loud (70 to 100 decibels), and they produce carbon monoxide—so they must run outdoors, at least 20 feet from windows and doors.
Gasoline portables are cheapest upfront but need refueling every 6 to 12 hours depending on load. Gasoline also degrades after 30 days in the tank, so you'll need to drain it or add stabilizer if the generator sits unused for months. Propane portables cost more but run longer on a tank and propane doesn't degrade; you can store a full tank for years. Diesel portables are efficient and fuel-efficient but less common and more expensive.
For extended outages, keep extra fuel on hand—but store it safely. Gasoline must go in approved metal or plastic cans in a shed or garage, never indoors. Propane tanks should be stored outdoors in a cool, dry place. Check your local fire code; some areas limit how much fuel you can store at home. During an outage, run the generator only when you need it to stretch fuel and reduce noise.
Standby generators: automatic backup and permanent installation
Standby generators are bolted to a concrete pad outside your home or business and connected to your electrical panel. They cost $3,000 to $15,000 or more installed, depending on size and fuel type. When power fails, they start automatically within seconds and switch your home to generator power; when the grid returns, they switch back and shut down. You don't have to do anything, and they're much quieter than portables (65 to 75 decibels).
Most standby generators run on natural gas or propane. Natural gas is convenient if your home already has a line—you don't store fuel, and the utility maintains pressure. The downside is that during a major outage, the gas utility might reduce pressure or shut off service to certain areas, leaving your generator without fuel. Propane standby generators need a large tank (usually 100 to 500 gallons) buried or sitting outside; you arrange refills with a propane company, so you're not dependent on the utility.
Installation requires a licensed electrician to run conduit from the generator to your panel, install a transfer switch (which disconnects the grid and connects the generator), and set up automatic starting. Some municipalities require a permit and inspection. Maintenance includes oil changes every 100 to 200 hours of use, filter replacements, and an annual load test to make sure the generator starts and runs properly.
Inverter generators for sensitive electronics and camping
Inverter generators produce power that mimics utility power more closely than standard generators do. They regulate voltage and frequency to stay within the narrow range that computers, phones, and medical devices need. Standard generators can produce power spikes that damage electronics; inverter generators keep output stable. This makes them essential if you need to run a laptop, CPAP machine, insulin pump, or other sensitive equipment during an outage.
Inverter generators are portable, usually weighing 50 to 80 pounds, and cost $1,000 to $4,000 depending on wattage. They're quieter than standard portables (53 to 75 decibels) because they run at variable speed—the engine slows when demand is low, using less fuel and making less noise. They're popular for camping, RVing, and tailgating as well as home backup.
The downside is higher cost and lower wattage per dollar. Most inverter generators max out at 4,000 to 6,000 watts, so they won't run large loads like air conditioning or electric heat. They also take longer to refuel and maintain than larger standby units. If you need both clean power and high wattage, you'll pay more than for a standard generator of the same size.
Installation, safety, and maintenance basics
Portable generators must always run outdoors, at least 20 feet away from windows, doors, and vents. Carbon monoxide is odorless and can kill in minutes; it seeps through walls and into homes. Never run a generator in a garage, basement, or shed, even with the door open. Use heavy-duty outdoor extension cords rated for wet conditions, and keep the generator on level ground away from water and debris.
Standby generators need professional installation by a licensed electrician. The transfer switch is critical—it prevents backfeed, which occurs when generator power flows backward into the utility lines and can electrocute utility workers. A manual transfer switch requires you to flip a lever to switch between grid and generator; an automatic transfer switch does this instantly when power fails. Automatic switches cost more but are safer and more convenient.
Maintenance keeps your generator ready when you need it. For portables, change the oil before first use and every 50 to 100 hours after. Drain the fuel tank or add stabilizer before storing for more than 30 days. For standby units, schedule an annual service with a technician who will change oil, replace filters, test the battery, and run a load test. Keep records of all maintenance so you know when the next service is due.
Fuel costs and long-term operating expenses
The cost to run a generator depends on fuel price, generator efficiency, and load. A 5,000-watt portable running at half load on gasoline at $3 per gallon might cost $1 to $2 per hour. A 20,000-watt standby running on propane at $2.50 per gallon might cost $3 to $5 per hour at full load. During a week-long outage, fuel costs can add up quickly, so it's worth thinking through how long you expect to run the generator and how often outages happen in your area.
Natural gas standby generators are cheapest to operate because you don't buy fuel in bulk—you pay the utility rate, which is usually lower than propane or gasoline per unit of energy. Propane is more expensive per gallon but stores indefinitely, so you're not replacing fuel every season. Gasoline is cheapest upfront but degrades, requires frequent refueling, and costs more per hour to run than propane or natural gas.
If outages are rare in your area, a portable generator makes financial sense—you spend less upfront and only pay for fuel when you use it. If outages are frequent or last days at a time, a standby generator pays for itself over time by reducing fuel costs and the labor of refueling and maintaining a portable.
Frequently Asked Questions
Can I run a generator in my garage or basement during winter?
No. Generators produce carbon monoxide, which is colorless and odorless and can kill in minutes. It seeps through walls and into homes even when doors and windows are closed. Always run the generator outdoors, at least 20 feet away from windows, doors, and vents, regardless of weather or season.
What's the difference between running watts and starting watts?
Running watts is the steady power a device uses once it's on. Starting watts is the extra power needed for the first few seconds when a motor turns on—a refrigerator might need 600 running watts but 2,000 starting watts. Your generator must handle the highest starting wattage of any device you turn on at the same time, plus the running wattage of everything else.
Do I need a transfer switch if I have a portable generator?
No, but you should never plug a portable generator into a wall outlet or connect it directly to your home's electrical panel. Use heavy-duty outdoor extension cords rated for wet conditions. A transfer switch is required only for standby generators to prevent backfeed, which can electrocute utility workers.
How long can I run a generator continuously?
Most generators are designed to run 8 to 12 hours at a time before needing an oil change or cooldown. Standby generators can run continuously for days or weeks if fuel is available and maintenance is kept up. Portable generators should be shut down for at least 30 minutes every 12 hours to cool and for oil checks.
What size generator do I need for a whole-house backup?
It depends on what you want to run. If you want essential circuits only—lights, refrigerator, furnace, and water heater—plan for 10,000 to 15,000 watts. If you want to run air conditioning or electric heat as well, you'll need 25,000 to 30,000 watts or more. An electrician can review your panel and recommend the right size for your home.