Electricity Generator for Home: Types, Sizing, and Backup Options

A power outage that lasts two hours is an inconvenience. One that lasts two days during a heat wave or winter storm becomes a genuine safety problem. How you respond to that difference depends almost entirely on what you prepared before the grid went down.

For most U.S. homeowners, that preparation involves some form of home electricity generator, though what that term means in practice ranges from a $500 portable unit to a $15,000 permanently installed standby system with automatic transfer.

This guide covers the full range of home backup technology, how to calculate what you actually need, what safe connection requires, and how battery backup compares to fuel generators across the scenarios that matter most to homeowners.

Key Takeaways

• Power in watts or kilowatts tells you what a generator can run at once. Stored energy in watt-hours or kilowatt-hours, or fuel capacity in gallons, tells you how long it can run. Both numbers are required for any useful backup plan.

• Essential-load backup is realistic for most homeowners. Whole-home backup of every circuit is a much larger and more expensive proposition. Define your priority loads before comparing products.

• Fuel generators must never be operated indoors or in attached garages. CPSC recommends operating portable generators outdoors only, at least 20 feet from homes and buildings, with exhaust directed away from windows, doors, and vents. CPSC documents ongoing generator-related carbon monoxide fatalities every year, including deaths from units operated in open garages with doors up.

• Battery backup systems produce no combustion exhaust during normal operation and generally operate at much lower noise levels than fuel generators, making them usable inside the home when operated according to the product's placement, ventilation, and safety instructions. They cannot run a whole house indefinitely but are the correct technology for essential electronics, refrigerators, compatible medical devices when the device manufacturer's backup-power requirements are met, and lighting during typical outages.

• Any connection to your home's electrical panel requires approved transfer or isolation equipment that prevents backfeeding and must comply with applicable electrical code, utility rules, and local permitting requirements. Panel-connected installations should be performed by a qualified electrician, and a licensed electrician may be required by the local jurisdiction. Backfeeding through a wall outlet endangers utility workers and must never be used.

What Types of Home Generators Are Available?

The term home electric generator covers meaningfully different technologies with different output levels, runtimes, installation requirements, and operating costs.

For current price context, a 3,500–4,000W portable fuel generator generally falls in the $600 to $1,300 range, while an installed home standby system typically costs around $8,000 to $16,000 including the generator. A 5–8kWh modular battery-backup system generally falls in the $2,500 to $4,500 range before additional home-integration hardware or installation. Actual pricing varies by model, capacity, installation complexity, location, accessories, permits, and promotions.

Permanent Standby Generators

Standby generators are permanently installed outside the home, connected to the natural gas or propane supply, and wired through an automatic transfer switch that detects a utility outage and starts the generator within seconds. Units sized for partial-home or whole-home coverage range from 7 kW to 26 kW or larger for residential use. Installation, including the transfer switch, electrical permit, gas permit, and pad, typically runs $5,000 to $15,000 or more depending on unit size, local labor rates, and any required gas line work.

Standby generators run as long as the fuel supply is maintained and require annual servicing to remain ready. They are the most capable and most automatic option for whole-home backup but also the most expensive and should be professionally installed in compliance with applicable local code and permitting requirements.

Portable Fuel and Inverter Generators

Portable generators in the 3,500W to 12,000W range are gasoline or dual-fuel (gasoline and propane) units that can be stored and deployed when needed. They require manual starting, outdoor placement, extension cords or a transfer switch for connection, and manual refueling.

Conventional portable generators produce variable power output and relatively high harmonic distortion, making them less suitable for sensitive electronics. Inverter generators produce cleaner, more stable AC power that can support sensitive electronics and compatible medical equipment when the device manufacturer's power, waveform, grounding, and backup requirements are met, but most inverter models are limited to 2,000W to 7,000W of output.

Both types produce carbon monoxide. CPSC warns in its 2026 generator safety advisory that even generators operated with an open garage door can produce lethal concentrations of CO inside the structure within minutes. CPSC recommends operating portable generators outdoors only, at least 20 feet from homes and buildings, with exhaust directed away from windows, doors, and vents.

Battery Backup and Solar Generators

Battery backup systems use stored electrical energy from LFP or other lithium-ion cells. They produce no combustion exhaust during normal operation and generally operate at low noise levels, with cooling-fan noise varying by load and charging conditions. Compatible units can be used indoors when operated according to their product placement, ventilation, and safety instructions. Transfer time is model-dependent: the Apex 300 supports 0ms or approximately 20ms UPS switching depending on mode and outlet configuration, while the Elite 400 has a 15ms UPS.

Their runtime limitation is determined by stored energy, not fuel. A 3,000 Wh battery running a 300W continuous load has a theoretical runtime of approximately 10 hours before conversion losses. At 90% system efficiency, the same example is approximately 9 hours before any additional reserve is retained — though actual runtime depends on device wattage, ambient temperature, battery condition, and inverter efficiency under real-world conditions.

Recharging requires either grid power restoration, a generator connection, or solar input if panels are available.

Solar generators combine a battery power station with solar input capability. During daylight, solar panels recharge the battery, potentially allowing indefinite operation of lower-power loads even during extended outages.

What Size Home Generator Do You Need?

Choose Essential Loads or Whole-Home Coverage

Most homeowners do not need whole-home backup. They need to keep the refrigerator running, maintain internet and communications, power essential lighting, run compatible CPAP or other medical devices when their specified backup-power requirements are met, and stay comfortable enough to remain safely at home during the outage. Sizing for those specific loads costs significantly less than sizing for every circuit in the house.

Whole-home coverage requires accounting for the largest motor loads in the building: HVAC equipment, a well pump if present, and an electric stove or dryer if applicable.

A central 4-ton air conditioner running on a 240V circuit can draw 3,000 to 5,000W continuously and require 2 to 3 times that for startup. Any generator or battery system claiming to power central AC needs to document its output and surge capability against the specific equipment's nameplate data, not a generic estimate.

Essential Load Worksheet

Replace every value with nameplate or manual data for your actual appliances. Starting watts applies only to motor loads during startup.

The listed running loads total about 380W when operating simultaneously, while the daily energy values based on the stated runtimes total approximately 5,615 Wh per day. For a 3-day outage, total energy needed is approximately 16,845 Wh (16.845 kWh) before accounting for conversion losses.

Estimate Outage Energy and Runtime

Assuming 85 to 90% overall system efficiency to account for inverter and battery conversion losses, a 16.845 kWh load requirement becomes approximately 18.7 to 19.8 kWh of nameplate battery capacity needed. That is a larger system than most single portable power stations provide, which is why expansion batteries or a generator for periodic recharging are part of any serious multi-day backup plan.

How Home Backup Systems Connect Safely

Extension Cords for Individual Loads

The simplest approach: run a portable generator outdoors only, at least 20 feet from homes and buildings, with exhaust directed away from windows, doors, and vents, and use heavy-duty extension cords to power individual appliances.

This requires no electrical installation, no permit, and no transfer switch. The limitation is that it only powers the devices physically connected to the extension cord. Nothing wired into the house circuits receives power this way.

For a battery power station placed inside the home, the same principle applies: plug devices directly into the station's outlets. No modification to house wiring is needed.

Transfer Switches, Inlets, and Permanent Systems

To power house circuits, including lights wired into the ceiling, hardwired appliances, and hardwired well pumps, a proper connection to the home's electrical panel is required.

This means approved transfer or isolation equipment, such as a transfer switch, generator interlock kit, or utility-approved transfer device, that physically prevents the generator from being connected to the utility while utility power is present.

An automatic transfer switch (ATS) detects a grid outage and automatically switches the panel to generator or battery power. Manual transfer switches require the homeowner to manually connect the generator and switch the panel over.

Panel-connected equipment should be installed by a qualified electrician and must comply with applicable electrical code, utility rules, and local permitting and inspection requirements; a licensed electrician may be required by the local jurisdiction. Backfeeding through a wall outlet, by plugging a generator's output into a dryer outlet to backfeed the panel, can energize utility lines and endanger utility workers attempting to restore power, so it must never be used.

Fuel Generator vs. Battery Backup

Battery backup works best when the outage is predictable in duration, solar recharging is available to extend runtime, or emissions and noise preclude a fuel generator. Fuel generators work best for extended outages where fuel is accessible, and the runtime requirement exceeds what stored battery capacity can provide.

BLUETTI Home Backup Options

Apex 300 for Modular and Expandable Backup

The BLUETTI Apex 300 is a 2,764.8 Wh LFP power station with 3,840W of continuous AC output, 7,680W Power Lifting for supported pure-resistive loads, and simultaneous 120V and 240V output. Its 0ms or approximately 20ms UPS switching, depending on UPS mode and outlet configuration, can support sensitive electronics and other compatible equipment whose transfer-time requirements are met. For medical equipment, follow the device manufacturer's specified backup-power requirements. The Apex 300 accepts up to 2,400W of direct solar input and integrates with the SolarX 4K charge controller for larger rooftop arrays.

The Apex 300 forms the core of BLUETTI's expandable backup power for home lineup.

B500K for Compatible Runtime Expansion

The BLUETTI B500K is a 5,120 Wh LFP expansion battery compatible with the Apex 300. Adding one B500K brings total system capacity to 7,884.8 Wh. Adding two brings it to 13,004.8 Wh. At 13,004.8 Wh with the essential-load example above (5,615 Wh per day), the system provides approximately 2.08 days of essential-load backup before depletion.

This estimate assumes the 90% system efficiency factor used throughout this article. Actual runtime depends on your specific appliance wattages, ambient temperature, battery state of health, and usage pattern. Solar input during daylight extends runtime further. The B500K does not provide standalone AC output and requires a compatible host system for AC appliances; with compatible ecosystem components such as Hub D1, it can also provide DC power.

Elite 400 for Portable Essential-Load Backup

The BLUETTI Elite 400 is a 3,840 Wh portable power station with 2,600W continuous output and 3,900W Power Lifting mode. Its built-in wheels and telescoping handle make it easy to move through the home.

At 3,840 Wh, it provides approximately 7.3 hours of the essential-load example above before reaching 20% reserve, assuming the 380W continuous example load and 90% system efficiency. Actual runtime varies with your specific appliance wattages, temperature, and usage pattern. It recharges to 80% in about 70 minutes using simultaneous AC and solar input.

The Elite 400 is best understood as a high-capacity portable unit for essential electronics, refrigerator, and compatible medical-device backup when the device's specified power requirements are met during shorter outages rather than a multi-day whole-home solution.

Home Generator Safety Checklist

• Running a generator safely requires more than reading the manual. Apply these requirements before and during every use:
  
  

• Never operate a fuel generator inside or in an attached garage, even with the door open. CO accumulates faster than most people expect.
  
  

• Install a battery-powered carbon monoxide detector on every level of the home and outside sleeping areas. CO is odorless and colorless.
  
  

• Use approved transfer or isolation equipment for any panel connection. Never backfeed through a wall outlet.
  
  

• For permanent standby systems, confirm annual servicing and load testing to verify the unit starts and transfers correctly.
  
  

• Store only the quantity of fuel permitted by your local fire code. Use fuel stabilizer if storing gasoline for more than 30 days.
  
  

• Never refuel a generator while it is running. Turn it off and let it cool before refueling.
  Operate portable generators outdoors only, at least 20 feet from homes and buildings, with exhaust directed away from windows, doors, and vents.
  
  

• For battery stations placed inside the home, check that ventilation around the unit is not blocked. Though they produce no combustion exhaust, lithium batteries perform best and safest within their rated temperature range.

Conclusion

The right home electrical generator depends on three decisions made in the right order: which loads need backup power, how long they need to run, and how they connect safely to your home.

Whole-home coverage requires a large standby generator and professional installation. Essential-load coverage is achievable with portable fuel generators, battery backup systems, or a combination of both. Battery backup provides no combustion exhaust during normal operation and generally offers much lower noise levels than fuel generators, making compatible systems suitable for indoor backup use when product instructions are followed. Fuel generators provide extended runtime wherever fuel is available.

Define essential loads first. Calculate energy needs second. Choose connection method and technology third.

Frequently Asked Questions

What size generator is needed to power a house?

Whole-home backup requires enough output to handle your largest motor loads simultaneously. A 3-ton central air conditioner at 240V draws 2,400 to 3,500W running and may require 6,000 to 9,000W to start. Add the refrigerator, water heater, lighting, and other loads for a complete picture. Most homes with central air conditioning require 10,000 to 22,000W of generator output for full coverage. For essential loads only, 3,000 to 6,000W covers most households. Use actual appliance nameplate data, not generic estimates.

Can a portable generator power central air conditioning?

Possibly, but only if the generator's continuous output and surge capability exceed the AC system's running watts and starting watts, and only if the connection is made through approved transfer or isolation equipment at the correct voltage. A 240V central AC system cannot run from a 120V-only generator. Confirm the starting current from the AC unit's nameplate, match it to a generator with verified surge capability, and have a qualified electrician install the applicable transfer or isolation equipment in compliance with local requirements.

Is a battery backup better than a gas generator?

It depends on the outage scenario. For outages under 24 hours with essential loads, a battery backup is cleaner, quieter, more automatic, and safer indoors. For multi-day outages where fuel is available and runtime must exceed stored battery capacity, a fuel generator provides longer coverage. Many homeowners use both: the battery backup handles day-to-day outages automatically, while the generator is available for extended emergencies.

How long can a home battery run a refrigerator and lights?

For the Apex 300 at 2,764.8 Wh: a refrigerator averaging 150W and 60W of LED lighting total 210W continuous. Dividing 2,764.8 Wh by 210W and applying a 90% system efficiency factor and retaining a 10% reserve gives approximately 10.7 hours of runtime.

This is a scenario estimate. Actual runtime depends on your refrigerator's real average draw, ambient temperature, battery condition, and usage pattern. Refrigerators with older or larger compressors draw more than the 150W example used here. Adding expansion batteries multiplies this proportionally. Solar input during daytime extends runtime further.

Do you need a transfer switch for a home generator?

For individual appliances powered by extension cords, no. For any connection to house circuits through the electrical panel, approved transfer or isolation equipment is required to prevent backfeeding; depending on the setup, this may be a transfer switch, interlock, or utility-approved transfer device. Applicable electrical code, utility rules, and local permitting requirements determine the permitted installation method. Panel-connected installations should be performed by a qualified electrician, and a licensed electrician may be required by the local jurisdiction.