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An outage at dinner time is the wrong moment to learn the size of the generator you need, and how much power generator do i need is the question to answer before the lights go out: add the running watts of the loads you run together, check the surge watts for anything with a motor, and pick a unit whose running and peak figures cover both. This guide works through those figures step by step, using the sizes and figures the reference listings state.
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How much power generator do i need: the quick answer
Add the running watts of everything you want to run at the same time, then check the peak watts for the largest motor load, since motors pull a short spike at startup. The reference listings span from 2000 running watts for the Oxseryn 2800 (on Amazon) to 9500 running watts on gasoline for the Westinghouse 12500 (on Amazon), so the range covers a campsite and a home backup build. Size on the fuel you plan to burn: the Westinghouse lists 9500 running watts on gasoline and 8500 running watts on propane, so the propane figure is what matters for a propane plan.
Step 1: Add up the running watts you need
List the loads you want to run at the same time and add their running watts from each load label or manual. The reference listings show the spread of units you can match that total to:
| Unit | Running watts | Peak watts | Run time |
|---|---|---|---|
| Oxseryn 2800 | 2000 | 2800 | Up to 9 hours at 25% load |
| PowerSmart 3800 | 3200 | 3800 | Not stated |
| Oxseryn 4400 | 3400 | 4400 | Up to 14 hours at 25% load |
| Westinghouse 12500 | 9500 on gasoline, 8500 on propane | 12500 on gasoline, 11200 on propane | Up to 12 hours |
Pick a unit whose running watts cover your list with room to spare, not a unit whose peak watts merely match it. Running watts are the continuous figure; peak watts cover only the short startup spike.
Step 2: Check the surge for motors
Anything with a motor pulls more at startup than while running, so the peak figure decides whether it starts. The listings state both figures for each unit: the Oxseryn 4400 (on Amazon) lists 4400 peak watts and 3400 running watts, the PowerSmart lists 3800 starting watts and 3200 running watts, and the Westinghouse lists 12500 peak watts and 9500 running watts on gasoline. If the peak watts fall short, the generator stalls or shuts off when the motor kicks in, so compare the peak figure against the largest motor load, not against the running total.
Step 3: Match fuel, tank and run time
Fuel sets the watts: the Westinghouse lists 9500 running watts on gasoline and 8500 on propane, with 12500 peak watts on gasoline and 11200 peak watts on propane, so a dual-fuel unit bought for propane must be sized on its propane figures. Run time sets how much fuel you carry: the Oxseryn 2800 lists up to 9 hours at 25% load on a 1.1 gallon tank, the Oxseryn 4400 lists up to 14 hours at 25% load on a 2 gallon tank, and the Westinghouse lists up to 12 hours. Eco mode stretches a tank by slowing the engine when the load is light, which the Oxseryn and PowerSmart listings state.
Step 4: Check outlets, noise and weight
Outlets decide what you can plug in: the Westinghouse lists 2 GFCI 120V 20A household receptacles, a 120V 30A transfer-switch-ready outlet and a 120/240V 50A RV outlet, the PowerSmart lists a 120V 20A duplex, a 120V 30A twist-lock and a 12V 8A DC outlet with dual 5V 2.1A USB ports, and the Oxseryn units list 120V AC ports, a 12V DC port and an RV port. A transfer-switch-ready outlet connects to home wiring, so a licensed electrician should install it. Noise matters at a campsite: the Oxseryn 2800 lists under 58 dBA from 23 feet, the PowerSmart lists 59 dBA from 23 feet, and the Oxseryn 4400 lists under 72 dBA from 23 feet. Weight matters when you carry it: the PowerSmart lists 47.0 pounds and the Oxseryn 4400 lists 56.0 pounds, while the Oxseryn 2800 title says 39 lbs and its bullets say 40 lbs, so that listing disagrees with itself on weight. For sensitive electronics, the PowerSmart and Oxseryn 2800 list THD under 3%.
Where a fuel generator runs
Run a fuel generator outdoors only, far from doors and windows, because of carbon monoxide. Never use a fuel generator indoors or in a partly enclosed area.
Ways to keep the size down
- Run fewer loads at once: stagger the loads instead of starting everything together, so the running total stays inside the unit.
- Size on the fuel you burn: size on the propane figure for a propane plan, not the gasoline figure.
- Use Eco mode where the listing states it: the engine slows when the load is light, so a tank lasts longer.
- Check the outlets before the watts: a unit with the right watts and the wrong outlets still cannot run the load.
- Plan for altitude: the Oxseryn 2800 listing states that above 4000 feet a high-altitude kit is recommended, so check the manual if the site sits high.
FAQ: power away from the grid
What size generator do I need for a house?
It depends on the loads: add the running watts of everything you run together and check the peak watts for the largest motor. The listings here run from 2000 running watts for the Oxseryn 2800 to 9500 running watts on gasoline for the Westinghouse 12500, which lists transfer-switch-ready outlets for home backup.
What is the difference between running watts and peak watts?
Running watts are the continuous output, and peak watts are the short output for startup: the Oxseryn 4400 lists 4400 peak watts and 3400 running watts, and the PowerSmart lists 3800 starting watts and 3200 running watts. Size the running total on running watts and the largest motor on peak watts.
How long will a generator run on a tank?
It depends on tank size and load: the Oxseryn 2800 lists up to 9 hours at 25% load on a 1.1 gallon tank, the Oxseryn 4400 lists up to 14 hours at 25% load on a 2 gallon tank, and the Westinghouse lists up to 12 hours. Check the run time the listing states at the load you plan.
Do I size on gasoline or propane watts?
Size on the fuel you plan to burn: the Westinghouse lists 9500 running watts on gasoline and 8500 on propane, with 12500 peak watts on gasoline and 11200 on propane. A dual-fuel unit bought for propane must cover the loads on its propane figures.
How loud is a portable generator?
It depends on the unit: the Oxseryn 2800 lists under 58 dBA from 23 feet, the PowerSmart lists 59 dBA from 23 feet, and the Oxseryn 4400 lists under 72 dBA from 23 feet. Check the noise figure the listing states.
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