Published: 16.07.2026 · Motohill team · Updated: 24.10.2026
You size a generator in two steps: add up the wattage of the appliances that will run at the same time and add a 20–30% margin, then check that the generator's maximum output can cover the start-up surge of the largest motor-driven appliance (fridge, pump, compressor). For backup power in a house without a water pump, 2–3 kW of rated output is usually enough; with a borehole pump and more appliances, aim for around 5 kW.
Below you will find an approximate power table for household appliances, a step-by-step example, a comparison of conventional and inverter generators, and an overview of the WEIMA generators in our catalogue.
Rated power and maximum power: what is the difference?
Every generator has two figures in its specification. Rated power is the output the generator can deliver continuously, for many hours. Maximum power is available only for a few seconds, for example when an electric motor starts. Always choose a generator by its rated power. If your total load is close to the maximum figure, the overload protection will keep cutting out and the engine will run overloaded all the time.
Heating appliances without a motor (kettle, heater, light bulb) draw about the same when switched on as they do while running. Appliances with a motor or compressor (fridge, freezer, water pump, compressor, saw) briefly draw 2–3 times more at start-up. That is the most common reason why a generator that looks big enough on paper will not start a fridge or a pump.
Household appliance power table
The figures in the table are approximate and meant for a first estimate. Check the exact wattage of your own appliance on its rating plate or in the manual: it is given in watts (W).
| Appliance | Running power (approx.) | Start-up draw (approx.) |
|---|---|---|
| LED lighting, several rooms | 50–150 W | the same |
| TV, router, chargers | 50–200 W | the same |
| Laptop | 50–100 W | the same |
| Fridge or freezer | 100–300 W | 2–3 times more |
| Gas boiler with central heating pump | 100–200 W | slightly more |
| Borehole pump or pressure pump | 750–1500 W | 2–3 times more |
| Microwave oven | 1000–1500 W | the same or slightly more |
| Electric kettle | 1800–2200 W | the same |
| Drill, angle grinder | 600–2000 W | up to 2 times more |
| Electric saw, compressor | 1500–2400 W | 2–3 times more |
Example: how many kW does a house need during a power cut?
Let's say that during a power cut you want to keep running:
- a fridge: about 150 W,
- a gas boiler with heating pump: about 150 W,
- LED lighting in a few rooms: about 100 W,
- a TV, router and chargers: about 150 W.
Together that is about 550 W of continuous load. At start-up the fridge briefly needs about three times its running power, so another 300 W. A generator with 2 kW rated output will handle this easily, with some margin left for a microwave if you use it on its own.
If the house has its own well, add a borehole pump, for example 1100 W, which briefly needs more than 3 kW when it starts. The running total is then about 1.7 kW, but at the moment the pump starts the generator must deliver over 3.5 kW. A 2.8/3.2 kW unit would be at its limit, so a model with about 5 kW rated output is the safer choice, for example the WEIMA WM5500BE (5.0/5.5 kW).
A simple rule to finish the calculation:
- the generator's rated power should be at least 20–30% higher than the total running power of your appliances,
- the maximum power must cover that total plus the extra start-up draw of the largest motor-driven appliance,
- switch on high-power appliances (kettle, saw, compressor) one at a time, not all at once.
Conventional or inverter generator?
A conventional generator on an open frame with an automatic voltage regulator (AVR) is simple and robust, and usually cheaper per kilowatt. It copes well with pumps, power tools and work on a building site or farm. In our catalogue these are the WM2500B, WM3200B, WM3200BE, WM5500BE and WM8500E.
An inverter generator produces very stable power, which makes it better suited to appliances with electronics: boilers with a controller, computers, TVs. The WEIMA inverter models (WM2300iS, WM4000i, WM6000Ei) have a fuel-saving mode and can be linked for parallel operation through a connection block. At similar output they are lighter than conventional units, but more expensive.
| Feature | Conventional with AVR | Inverter |
|---|---|---|
| Voltage | regulated by AVR, fine for most appliances | very stable, safe for electronics |
| Typical use | home backup, building site, pumps, tools | boiler with controller, computer, TV, trips |
| Weight at similar output | higher (e.g. WM3200B: 45 kg) | lower (e.g. WM4000i: 35 kg) |
| Parallel operation of several units | no | yes, via connection block |
| Price per kilowatt | usually lower | usually higher |
WEIMA generators in the Motohill catalogue
| Model | Type | Rated / max. power | Starting | Weight |
|---|---|---|---|---|
| WEIMA WM2300iS | inverter | 2.0 kW | recoil | 18 kg |
| WEIMA WM2500B | conventional, AVR | 2.0 / 2.5 kW | recoil | 43 kg |
| WEIMA WM3200B | conventional, AVR | 2.8 / 3.2 kW | recoil | 45 kg |
| WEIMA WM3200BE | conventional, AVR | 2.8 / 3.2 kW | electric + battery | 45 kg |
| WEIMA WM4000i | inverter | 3.5 / 4.0 kW | recoil | 35 kg |
| WEIMA WM5500BE | conventional, AVR | 5.0 / 5.5 kW | electric + battery | 83 kg |
| WEIMA WM6000Ei | inverter | 5.5 / 6.0 kW | see product page | 65 kg |
| WEIMA WM8500E | conventional, AVR-4 | 7.5 / 8.5 kW | electric | 105 kg |
All of these generators are single-phase, with 230 V sockets and a 12 V output. For the WM4000i, WM6000Ei and WM8500E the manufacturer states a fuel consumption of 375 g/kWh. The full list with current data is in the generators category.
Safety and getting ready for winter
- Only run the generator outdoors, away from windows and doors. The exhaust contains carbon monoxide, which has no smell and can kill. Never run a generator inside a house, garage or cellar.
- Do not connect the generator to your home wiring through an ordinary socket. Powering a house requires a mains/generator changeover switch fitted by an electrician.
- Fill the engine with oil before the first start, and refuel only with the engine switched off and cooled down.
- If the generator is kept on standby, run it once a month for 10–15 minutes under a light load. On models with electric start, check the battery before winter.
Most power cuts come with autumn storms and winter icing, so it is best to buy and test a generator in advance. Before winter you may also find our guide how to choose a petrol snow blower useful.
Frequently asked questions
What size generator do I need for my house during a power cut?
For a fridge, gas boiler, lighting and TV, 2–3 kW of rated output is usually enough. If you also have a borehole or pressure pump, choose about 5 kW. If the boiler has an electronic controller, an inverter generator is the safer option.
Is a 3 kW generator enough for a house?
For the essentials, yes. It will not be enough if you switch on the kettle, the water pump and other high-power appliances at the same time. Add up your load using the table above and allow for start-up surges.
Can a generator run a borehole pump?
Yes, if the generator's maximum output covers the pump's start-up. An 1100 W pump briefly needs more than 3 kW when starting, so for a house with a well a generator of about 5 kW is the better choice.
Can these generators power three-phase equipment?
No. The WEIMA generators in our catalogue are single-phase, 230 V. Equipment rated at 400 V needs a three-phase generator.
What about delivery and warranty?
We ship by courier across Poland: free from 999 zł, otherwise 39 zł. Delivery to other EU countries is possible, with cost and timing confirmed when you order. Generators come with a 24-month warranty, and you can return a purchase within 14 days.
Need help choosing?
List the appliances you want to power and call us on +48 780 140 444. We speak Polish, Ukrainian and Russian and will help you work out the power you need. All models are in the generators category, and for pumping water out of a pond, cellar or ditch, take a look at our water pumps.