Portable Generator for Emergency: Complete Power Guide
How to choose and size a portable generator for emergencies — covering conventional, inverter, and solar generators with runtime math, wattage tables, CO safety, and maintenance.
The lights go out at 11 PM during an ice storm. Your refrigerator has 200 pounds of food. Your well pump is electric. The forecast says five more days of this.
The people who planned for this moment have a generator running — or a charged power station — and a plan for how long their fuel will last. Everyone else is calling hardware stores that went sold out four hours ago.
This guide covers how to choose, size, and safely run a portable generator for emergencies. It includes the runtime math, a complete wattage reference table, CO safety requirements, and how portable power stations fit into your planning when fuel isn’t an option.
Three Categories of Emergency Power
Every portable power solution falls into one of three categories. Your situation determines which one belongs in your preparedness plan.
| Type | Best For | Max Output | Noise | Fuel |
|---|---|---|---|---|
| Conventional generator | Extended outages, high-wattage loads | 3,500–17,500W | 65–75 dB | Gas, propane, dual-fuel |
| Inverter generator | Electronics, moderate loads, quiet operation | 1,000–7,000W | 50–60 dB | Gas |
| Portable power station | Short outages, apartments, zero emissions | 300–5,000W | Silent | Battery (solar/grid recharge) |
Conventional Generators
How they work: A gasoline (or propane) engine drives an alternator at fixed 3,600 RPM, producing 120V/240V AC power. Engine speed is constant regardless of load.
Typical runtime math:
A 3,500W generator at 50% load burns roughly 0.3–0.5 gallons per hour.
- 3.5-gallon tank at 50% load: 7–12 hours
- 5-gallon add-on tank: 10–17 hours
- 25 gallons stored: 50–85 hours (2–3.5 days of continuous use)
At 75% load, fuel consumption climbs — expect 25–35% shorter runtimes than the 50% figures.
Noise level: 65–75 dB at 23 feet — roughly equivalent to a running vacuum cleaner. Not subtle.
Fuel requirements: Requires fresh, stabilized gasoline (or propane for dual-fuel models). Fuel degrades in 30–60 days without treatment. Add fuel stabilizer at fill-up, not months later.
Best use case: Extended outages (3+ days), powering a sump pump or well pump, running a window AC unit, or covering high-wattage loads that battery systems can’t sustain.
Key limitation: Fuel dependency. During a widespread disaster, gas stations close or run dry. Your fuel stock determines your runtime.
Inverter Generators
How they work: The engine speed varies dynamically based on load. The generator produces raw AC power, converts it to DC, then inverts it back to clean 120V AC with less than 3% total harmonic distortion (THD). Conventional generators run at 10–25% THD.
Why THD matters: Sensitive electronics — laptops, CPAP machines, televisions, medical equipment — can be damaged by dirty power. Inverter generators are safe for all electronics. Conventional generators are borderline for sensitive equipment.
Runtime math:
A 2,000W inverter generator at 25% load (common for lights + phone chargers + router) often burns 0.1–0.15 gallons per hour.
- 1-gallon tank at 25% load: 6–10 hours
- Full 1-gallon tank at 50% load: 3–5 hours
Fuel efficiency at light loads is 20–40% better than equivalent conventional generators.
Noise level: 50–60 dB at 23 feet — roughly equivalent to a normal conversation. Usable in suburban environments without triggering immediate neighbor complaints.
Best use case: Short-to-medium outages (1–5 days) where the priority is safe power for electronics, quieter operation, or fuel efficiency. Honda EU2200i and Yamaha EF2200iS are the benchmark models. Honda’s parallel capability lets you link two units for 4,400W combined.
Key limitation: Cost premium (1.5–3x the price of equivalent conventional units) and lower max wattage ceiling.
Portable Power Stations (Battery “Solar Generators”)
How they work: A lithium battery pack (LiFePO4 or NMC chemistry) stores energy measured in watt-hours (Wh). An inverter converts DC battery power to 120V AC. Recharge via solar panels, grid AC, a car 12V port, or any combination.
The “solar generator” label is marketing. The unit is a battery with an inverter. Solar panels are sold separately and are optional.
Capacity vs. cost reference:
| Capacity | Price Range | Best For |
|---|---|---|
| 300–500Wh | $200–$400 | Phone/laptop/light charging, CPAP 1–2 nights |
| 700–1,200Wh | $700–$1,200 | Fridge cycling (4–6 hours), fan, router |
| 2,000–2,500Wh | $1,500–$2,500 | Fridge 8–12 hours, larger appliances |
| 3,600–5,000Wh | $2,500–$5,000+ | Near-whole-room coverage, medical equipment |
Brand overview:
- Jackery — Explorer series. Broad availability, good app ecosystem, NMC chemistry (slightly less cycle-life than LiFePO4). Strong on portability.
- EcoFlow — Delta series. Fastest recharge speeds in class (0–80% in 50 minutes on Delta Pro). LiFePO4 on newer units. Expandable battery capacity.
- Goal Zero — Yeti series. LiFePO4, rugged build, ecosystem depth (Link module, Yeti Pro expandable). Premium pricing.
For a detailed spec comparison with current pricing, see our guide to emergency portable power stations at OffGridEmpire.
Runtime math:
Runtime (hours) = Battery capacity (Wh) ÷ Device load (W) × Inverter efficiency (roughly 85–90%)
Example: 1,000Wh unit powering a 60W load = 1,000 ÷ 60 × 0.87 = approximately 14.5 hours.
Noise level: Silent. No combustion engine.
Best use case: Apartment dwellers with no outdoor space, short outages (1–3 days), powering medical devices (CPAP, oxygen concentrator), and supplementing fuel generators to reduce runtime hours.
Key limitation: Finite capacity without recharge. Solar recharge is weather-dependent and slow (a 400W panel input takes 5+ hours to fill a 2,000Wh unit in ideal conditions). Not suitable as the sole power source for multi-day high-load scenarios unless paired with adequate solar.
For a side-by-side strategic comparison of all three options, see our solar vs generator vs battery comparison.
Generator Sizing: How to Calculate Your Wattage Needs
The critical distinction: running watts vs. starting watts.
- Running watts (also called rated watts): the continuous power required to keep the appliance operating
- Starting watts (also called surge watts): the brief spike required to start motor-driven appliances — typically 2–3x the running load, lasting 1–3 seconds
Your generator’s rated output must cover total running watts of everything running simultaneously. Its surge capacity must cover the highest starting load of any single appliance.
Wattage Reference Table
| Appliance | Running Watts | Starting Watts | Notes |
|---|---|---|---|
| Refrigerator (full-size) | 100–200W | 800–1,200W | Cycles on/off; size for surge |
| Chest freezer (7 cu ft) | 30–100W | 150–500W | More efficient than upright |
| Sump pump (1/3 HP) | 800W | 1,300W | Critical in flood/storm events |
| Sump pump (1/2 HP) | 1,050W | 2,150W | Size generator for this surge |
| Well pump (1/2 HP) | 1,000W | 2,100W | Most critical rural appliance |
| Window AC (5,000 BTU) | 500W | 1,500W | High surge relative to run load |
| Window AC (10,000 BTU) | 1,000W | 2,500W | — |
| Space heater (electric) | 1,500W | 1,500W | No surge; heavy continuous load |
| Box fan | 100W | 100W | No surge |
| LED lights (10 bulbs) | 80–100W | 80–100W | No surge |
| Phone charger | 5–20W | 5–20W | Negligible |
| Laptop | 45–90W | 45–90W | No surge |
| Wi-Fi router | 5–20W | 5–20W | — |
| CPAP (no heat) | 30–60W | 30–60W | Low draw; inverter generator recommended |
| CPAP (with heat) | 100–215W | 100–215W | — |
| Microwave (800W) | 1,000W | 1,000W | No surge |
| Electric water heater | 4,000W | 4,000W | Requires 240V; needs large generator |
| Central AC (3-ton) | 3,500W | 10,000W+ | Rarely practical with portable generators |
| Furnace blower only | 600–800W | 1,200–1,400W | Requires transfer switch |
Sizing example:
Goal: power refrigerator + sump pump + 10 LED lights + phone chargers + Wi-Fi router.
- Running total: 150 + 1,050 + 100 + 40 + 20 = 1,360W
- Highest single surge: sump pump at 2,150W
- Recommended generator: 3,500W rated / 4,000W surge — covers all loads with margin
Never run a generator at 100% rated load continuously. Stay at 80% or below for longevity.
CO Safety: The Cardinal Rule
Carbon monoxide (CO) is colorless, odorless, and kills faster than almost any other common household hazard. Generators are one of the leading causes of CO poisoning deaths in the United States during storm events.
The rule is absolute: Never run a generator indoors, in a garage (even with the door open), in a basement, in a carport, or under a covered deck.
Minimum distance: 20 feet from any window, door, or vent — measured in all directions, not just straight ahead. Point the exhaust away from the structure.
Why the garage-door-open approach kills people: CO from a generator reaches dangerous concentrations inside an attached garage in 3–5 minutes. The gas then seeps through wall gaps into the living space. It accumulates in bedrooms while occupants sleep. FEMA data shows this is the most common generator fatality scenario.
CO detector requirement: Install battery-operated CO detectors on every level of the home and near sleeping areas. Test them before each use season. Replace batteries annually.
Wet weather operation: Never run a generator in rain or standing water. Use a generator tent or canopy designed for wet-weather use — not a standard tarp rigged over the unit.
Transfer Switch vs. Extension Cords
Extension cords are appropriate for:
- Powering individual portable appliances directly from the generator
- Temporary setup during outages
- Any load that doesn’t require hardwired connection
Use 12 AWG or heavier cords rated for the load. Undersized extension cords overheat and cause fires. Never daisy-chain extension cords. Never run cords under rugs or through windows where they can be pinched.
Transfer switch is required for:
- Well pumps, sump pumps, and furnace blowers (hardwired appliances)
- Powering your home’s circuits without running cords through the house
- Safe, legal whole-home backup power
A manual transfer switch isolates your home from the utility grid and allows the generator to power selected circuits. Cost: $200–$500 installed by an electrician.
An interlock kit is a code-compliant alternative that prevents your main breaker and generator breaker from being on simultaneously. Cost: $50–$150 plus installation. Not available for all panels.
Never backfeed power through a wall outlet. Backfeeding sends live voltage into the utility grid and can electrocute lineworkers restoring power blocks away. It also voids your homeowner’s insurance and is illegal in every jurisdiction.
Generator Maintenance
A generator that won’t start during an emergency is worse than no generator — it’s a false sense of security.
Oil change intervals:
- Break-in: first 5 hours of operation, then drain and refill
- Standard: every 50–60 hours of runtime, or at the start of each season
- Use the oil weight specified in your owner’s manual (typically SAE 10W-30 for most conditions)
Monthly test run:
- Run the generator under load for 15–30 minutes every 30 days
- Check oil level before starting
- This keeps the carburetor lubricated, the battery (if electric start) charged, and confirms it’s operational
Fuel stabilizer — non-negotiable:
- Add fuel stabilizer at fill-up, not months later
- STA-BIL 360 or PRI-G are proven performers (see our gas stabilizer comparison)
- E10 gasoline without stabilizer degrades in 30–60 days; carb varnish is the leading cause of generator failure at start-up
Storage preparation:
- For storage longer than 30 days: either drain the fuel system completely, or fill the tank and treat with stabilizer
- Empty tank storage prevents varnish buildup but can allow gasket/seal drying in hot climates
- Full stabilized tank is preferred for emergency readiness — the generator is always fuel-ready
- Change the air filter annually
- Check and clean spark plugs annually or every 100 hours
Checklist for each use season:
- Oil changed or verified at correct level
- Fresh stabilized fuel in tank
- Air filter clean
- Spark plug condition checked
- Test run completed under load
- CO detector batteries tested
- Extension cords and transfer switch verified
Choosing Your Setup
Scenario 1 — Short outage, urban or suburban, no generator noise tolerance: Portable power station (1,000–2,000Wh). Power essentials: phones, router, CPAP, LED lighting. Recharge from solar if outage extends. EcoFlow Delta 2 or Bluetti AC180 are capable starting points.
Scenario 2 — 3–7 day outage, suburban home, refrigerator and sump pump critical: Dual-fuel conventional generator (3,500–5,500W) with 25 gallons of stabilized fuel. Add a 1,000Wh power station for overnight quiet use while the generator rests. Manual transfer switch for sump pump and furnace blower.
Scenario 3 — Extended outage, rural, well pump dependent: 5,500–8,000W conventional generator with 50-gallon fuel reserve and stabilizer rotation. Transfer switch. Consider propane conversion for a dual-fuel unit if you have a large propane tank — propane stores indefinitely.
Scenario 4 — Long-term off-grid preparedness: Solar panels plus a 2,000–5,000Wh battery system as the primary source, with a generator as backup. Eliminates fuel dependency for routine power needs while the generator handles high-load bursts. OffGridEmpire tracks current pricing and specs for emergency portable power stations if you’re comparing battery system options.
Bottom Line
The right emergency generator for your situation depends on three variables: how long the outage might last, what loads you need to power, and whether you can store and rotate fuel.
For most suburban households, a 3,500–5,500W dual-fuel generator paired with a 25-gallon fuel supply covers the realistic outage window. Add a portable power station for quiet overnight hours and electronics. Install CO detectors before the storm, not during it.
The fundamental mistake is waiting until the outage to start planning. Generator stock sells out in the first six hours of a major storm forecast. Fuel sells out in twelve.
Build your plan now, size it against the wattage table above, and test run the generator monthly so you know it’ll start when you need it.
Frequently Asked Questions
How do I calculate what size generator I need?
Add up the running watts of every appliance you plan to power simultaneously, then identify the single appliance with the highest starting watt surge. Your generator's rated wattage must exceed the running total, and its surge capacity must cover the highest starting load. A refrigerator (700W running, 2,200W starting), sump pump (1,050W running, 2,100W starting), and five LED lights (50W) requires at least a 2,000W generator with 2,200W surge — meaning a 3,500W unit gives you comfortable headroom.
How long will a generator run on a tank of gas?
Runtime depends on load and tank size. At 50% load, a typical 3,500W generator burns 0.3 to 0.5 gallons per hour. A 3.5-gallon tank lasts 7 to 12 hours. At 75% load, expect 5 to 8 hours. Inverter generators are 20 to 40% more fuel-efficient at partial loads due to variable engine speed. Always check your model's specific fuel consumption chart, which is measured at 25% and 50% load.
Is it safe to run a generator in the garage with the door open?
No. The garage-door-open myth kills people every year. Carbon monoxide from a generator can reach lethal concentrations inside an attached garage in minutes, and CO seeps through wall gaps into living spaces. FEMA and the CDC are unambiguous: generators must run outdoors, at least 20 feet from any window, door, or vent. Point the exhaust away from the structure.
What is the difference between an inverter generator and a conventional generator?
A conventional generator runs the engine at fixed RPM (3,600 RPM) regardless of load. An inverter generator uses electronic throttle control to match engine speed to actual demand, producing clean sine-wave power (less than 3% THD). Inverter generators are quieter (50 to 60 dB vs. 65 to 75 dB), 20 to 40% more fuel-efficient at light loads, and safe for sensitive electronics like laptops, CPAP machines, and TVs. They cost more and max out around 7,000W — conventional units scale to 17,500W.
Can a portable power station run a refrigerator?
Yes, but briefly. A standard refrigerator draws 100 to 200 watts while running but surges to 800 to 1,200 watts on compressor startup. A 1,000Wh power station rated at 1,200W output can cycle a refrigerator for roughly 4 to 6 hours — not continuously, but if you run it periodically to keep food cold, a 1,000Wh unit buys meaningful time. A 2,000Wh unit (EcoFlow Delta Pro, Bluetti AC200MAX) gives you 8 to 12 hours of intermittent refrigerator cycling.
Do I need a transfer switch to use a generator?
You need a transfer switch to power hardwired circuits in your home — things like a well pump, furnace blower, or central AC. Without one, use heavy-gauge extension cords (12 AWG or heavier, rated for the load) to run individual appliances directly from the generator. Never backfeed power into a wall outlet. Backfeeding can electrocute utility workers restoring power and will destroy the generator. A manual transfer switch runs $200 to $500 installed; an interlock kit is $50 to $150.