Generator size for 6000 running watts with a 1½ HP motor on propane
| Running wattseverything on at once | 6,000W |
|---|---|
| Starting surgerunning load plus the 1.5 HP motor's inrush | 8,238W |
| After the 80% rulea generator should not run continuously above 80% of its rating | 7,500W |
| Propane deratestores indefinitely; about 10% less output than petrol | −10% |
| Altitude derate2,000 ft at 3% per 1,000 ft | −6% |
| Rated size needed | 9,738W |
| Nearest size sold3% headroom left | 10,000W |
- Running watts
- 6000 W
- Largest motor
- 1½ HP
- Fuel
- propane
- Altitude
- 2000 ft
Read this before the numbers
Carbon monoxide kills people every storm season. Outdoors only, at least 20 feet from any door, window or vent, exhaust pointed away from the house. Not in a garage, not even with the door open. Fit CO alarms indoors and treat a headache during an outage as CO until proven otherwise.
Never back-feed. Plugging a generator into a wall socket energises the utility line outside and can kill a lineman restoring your power. A transfer switch or interlock kit is the only correct connection, and it is an electrician's job.
Two numbers, not one
6,000 W running — everything on at once. 8,238 W starting — the running load plus the inrush of the single largest motor.
Only one motor's surge is counted, and that is deliberate. A motor draws about three times its running watts for a second or two on start; adding every motor's surge together, which is what most sizing tables do, buys a generator twice the size you need.
Then the derates
The 80% rule first: a generator should not run continuously above 80% of its rating, because heat is what ends them. Then fuel — propane costs 10% of output against gasoline on the same engine. Then altitude, about 3% per 1,000 ft.
That comes to 9,738 W of rated capacity, so the size to buy is 10,000 W, leaving 3% headroom.
Inverter or conventional
Inverter generators are quieter, produce clean power for electronics, and throttle down under light load. They cost more per watt and top out lower. For a fridge, a furnace fan and lights, an inverter unit is usually the better buy. For a well pump and central air, it usually is not.
Fuel choice is a storage decision
Gasoline makes the most power and stores the worst — it needs stabilizer and rotation. Propane stores indefinitely and costs about 10% of output. Natural gas never runs out but costs 20% and needs a gas line. Diesel lasts longest and starts worst in cold.
Notes
- **Carbon monoxide kills people every storm season.** Run it outdoors only, at least 20 feet from any door, window or vent, with the exhaust pointed away from the house. Not in a garage — not even with the door open. Fit CO alarms indoors, and treat a headache during a power cut as CO until proven otherwise.
- **Never back-feed.** Plugging a generator into a wall socket to power the house energises the utility line outside and can kill a lineman working to restore your power. It is illegal almost everywhere for that reason. A transfer switch or an interlock kit is the only correct connection, and it is an electrician's job.
- Only the largest motor's inrush is counted, and that is deliberate. A 1.5 HP induction motor draws about 3,357 W for a second or two on start — roughly three times its running draw. Adding every motor's surge together, which is what most sizing tables do, buys you a generator twice the size you need and burns fuel accordingly.
- Propane: stores indefinitely; about 10% less output than petrol. The 10% derate is real — the same engine makes less power on this fuel, and it is already in the number above.
- The 80% rule is not caution. A generator held at its nameplate rating runs hot, and heat is what ends them. Sizing to 7,500 W of rated capacity for 6,000 W of load is what the machine is designed around.
- Inverter generators change the arithmetic. They are quieter, produce clean power for electronics, and throttle down under light load — but they cost more per watt and top out lower. For a fridge, a furnace fan and some lights, an inverter unit is usually the better buy; for a well pump and central air, it usually is not.
Nearby sizes
- Generator size for 5500 running watts with a 1½ HP motor on propane
- Generator size for 6500 running watts with a 1½ HP motor on propane
- Generator size for 5000 running watts with a 1½ HP motor on propane
- Generator size for 7000 running watts with a 1½ HP motor on propane
- Generator size for 6000 running watts with a 1 HP motor on propane
- Generator size for 6000 running watts with a 2 HP motor on propane
- Generator size for 6000 running watts with a ¾ HP motor on propane
- Generator size for 6000 running watts with a 3 HP motor on propane
- Generator size for 6000 running watts with a 1½ HP motor on gasoline
- Generator size for 6000 running watts with a 1½ HP motor on natural gas
- Generator size for 6000 running watts with a 1½ HP motor on diesel
- Generator size for 6000 running watts with a 1½ HP motor on propane
- Generator size for 6000 running watts with a 1½ HP motor on propane
- Generator size for 6000 running watts with a 1½ HP motor on propane
Read more
- MPPT or PWM: What the Extra Cost Actually BuysOne of these converts surplus voltage into extra current. The other throws it away. That single difference decides which one belongs in your system.
- Grid-Tied, Hybrid or Off-Grid: Three Systems, Three Different BudgetsThe most common surprise in residential solar is discovering that a grid-tied array does nothing during a blackout — and that it is designed that way on purpose.
- Roof Space for a 10 kW Array: Panel Area Is Not Roof AreaTwenty-five panels cover about 525 square feet. The roof they need is closer to 680, and the gap is mostly required by code rather than by geometry.
- Daily Solar Output by Region, and the Seasonal Swing Behind the AverageAn annual average tells you what the system produces over a year. It tells you almost nothing about December, and December is where the sizing arguments happen.