What Size Generator for a House in Thailand? Running vs Starting Watts
Figures reviewed 14 October 2026
Two ratings to compare
Every generator has two ratings:
Running (continuous) watts: what it can supply for hours.
Starting (surge) watts: a short burst for motors as they start up.
Your loads have to fit both ratings.
Running load = the total running watts of everything switched on together. Starting estimate = the running load + the largest extra starting demand of any single appliance.
"Extra" means the amount above that appliance's running watts. If a pump runs at 500 W and takes 1,700 W to start, the extra is 1,200 W. Don't add the full 1,700 W, because that counts its 500 W twice.
Calculator default example: 1,800 W running + 1,200 W extra start = 3,000 W starting needed.
Example for a Thai house
These wattages are illustrative. For a pump, use electrical input watts and its real start demand; motor shaft horsepower, marketing kW and aircon BTU are not interchangeable.
| Appliance | Running W | Extra start W |
|---|---|---|
| Water pump | 400 | 800 (example) |
| Fridge | 150 | 450 (example) |
| 2 fans | 120 | — |
| LED lights | 60 | — |
| Router and chargers | 30 | — |
| Total | 760 W | largest extra: 800 W |
Starting estimate: 760 + 800 = 1,560 W. Treat 760 W running and 1,560 W starting as preliminary minimums to compare, then confirm appliance start demand, outlet rating, voltage/phase and generator specifications.
In a house with a tank and pump, the pump may decide the generator size if its start demand is the largest. Check the actual equipment.
Safety rules
Outdoors only: keep the generator at least about 6 m (20 ft) from doors, windows and vents, with exhaust pointed away, and use a working carbon-monoxide alarm. Follow its manual too; an open garage is unsafe.
Never back-feed: don't plug a generator into a household socket to power the house. It can kill utility workers and damage equipment. A whole-house connection needs a transfer switch installed by a qualified electrician.
Check the outlets: a single outlet on the generator may be rated lower than the whole machine.
Fuel: store it safely, and let the engine cool before refuelling.
FAQ
Should I add every appliance's starting watts? No. The calculator assumes appliances start one at a time, so only the largest extra start counts. If several motors start together, have the load assessed professionally.
If my loads fit, is the generator safe to connect? Not necessarily. Check voltage, phase, protection and connection method with a qualified electrician. PEA describes a 230/400 V, 50 Hz system; verify your local supply, appliance nameplates and generator output.
Check 760 W running and 800 W extra start