Guide · Generators
How to choose a generator for your home
For a home, choose a generator whose continuous (rated) output is greater than the sum of the devices you want to power at the same time, with a margin for the starting surge of a refrigerator, pump or air conditioner motor. For basic supply (refrigerator, lighting, router, gas boiler) an inverter of about 2 kW is usually enough, and for a well pump, air conditioning or three-phase equipment count on a generator of 5 kW or more.
- Selection criterion
- continuous (rated) power
- Margin
- motor starting surge + about 20%
- Prices in the guide
- October 2026
Step 1: list what you want to power
Write down the devices that must keep working when the power fails, not everything you have in the house. Read the exact power from the device plate or label (W or kW). The values in the table are approximate ranges for comparison, not a substitute for the plate.
| Device | Approximate continuous power | Motor starting surge |
|---|---|---|
| Refrigerator, freezer | 100 to 200 W | yes (compressor) |
| LED lighting | 5 to 15 W per bulb | no |
| Television | 50 to 150 W | no |
| Router and modem | 10 to 20 W | no |
| Gas boiler (electronics and pump) | 80 to 200 W | minor |
| Well pump, pressure booster pump | 750 to 1,100 W | yes, pronounced |
| Air conditioner | 700 to 1,200 W | yes (milder with inverter air conditioners) |
| Kettle | 1,800 to 2,200 W | no |
| Electric water heater | 1,500 to 3,000 W | no |
Devices with a heating element (kettle, water heater, oven) draw the most, but have no starting surge. It often pays to switch them off while the generator is running, so that a smaller model is enough.
Step 2: continuous and peak power
The manufacturer states two power figures. Taking the KSB 21i as an example, it is 2.0/1.8 kW: 2.0 kW is the maximum (peak) power the generator delivers for a short time, and 1.8 kW the rated power it delivers continuously.
Always make your choice by the rated power. The peak power is a reserve for short surges, not for continuous running.
Step 3: motor starting surge
When starting, an electric motor draws several times more current than when running, roughly 2 to 3 times, and for some pumps and compressors even more. This surge is brief, but the generator has to withstand it without a voltage drop.
- The most demanding are water pumps, refrigerators, freezers, compressors and older air conditioners.
- Inverter air conditioners and refrigerators usually start more gently.
- Start the largest motor first, and the other devices after it. Do not start several motors at the same time.
The exact starting current is sometimes in the device instructions. If it is not, allow a margin.
Step 4: a worked example
A house with a well wants to power a refrigerator (150 W), lighting (100 W), a television (100 W), a router (20 W), a gas boiler (150 W) and a well pump (1,000 W).
- Sum of continuous power: 1,520 W.
- The pump has the largest starting surge: with a factor of 3 at start it draws about 3,000 W, that is 2,000 W more than its continuous power.
- 1,520 W + 2,000 W = 3,520 W.
- 20% margin: about 4,200 W.
You need a generator with a rated output of at least 4.2 kW, for example the KS 7000E (5.5/5.0 kW) or the KS 5500iE S ATSR inverter (5.5/5.0 kW). Without the pump, the same list needs about 1 kW, which the KSB 21i covers. You can do the same calculation faster in the power calculator.
Step 5: single-phase or three-phase
If the house has only single-phase loads (230 V), take a single-phase generator. You need a three-phase (400 V) one only for three-phase equipment, for example a three-phase pump or boiler.
With a three-phase generator the power is divided among three phases, so single-phase devices cannot use the full output. Models marked 1/3, such as the KS 7000E-1/3, switch between 230 and 400 V and, according to the specification, deliver 5.5/5.0 kW in both modes.
Step 6: ATS, fuel, noise and run time
- ATS starts the generator by itself when the mains fails. You need it if nobody is at home or if you are powering a pump or boiler. More in the guide What is ATS.
- Fuel: petrol for occasional use, diesel for many hours, LPG when the fuel sits for a long time. A comparison is in the guide petrol, diesel or LPG.
- Noise: the manufacturer states two values (e.g. 63/88 dB for the KS 3100i S). The lower is the sound pressure level at a distance from the generator, the higher is the sound power level. Compare like with like.
- Run time in the specifications is at 50% load. The KS 7000E with a 25 l tank runs for about 17 h, the KS 3100i S with 4 l for about 2.7 h.
Examples from our range
Prices are valid at the time of writing (October 2026); the current price is on the product page.
| Use | Model | Output | Weight | Price |
|---|---|---|---|---|
| Refrigerator, lighting, router, boiler | KSB 21i | 2.0/1.8 kW | 21 kg | €485 |
| The same, quieter, parallel operation | KS 3100i S | 3.1/2.8 kW | 21.5 kg | €882.50 |
| With a well pump | KS 7000E | 5.5/5.0 kW | 76.2 kg | €1,031.25 |
| With a pump, inverter with an ATS output | KS 5500iE S ATSR | 5.5/5.0 kW | 52 kg | €1,650 |
| Three-phase loads | KS 7000E-1/3 | 5.5/5.0 kW | 81 kg | €1,357.50 |
| Longer running, diesel, ATS output | KS 9200HDES-1/3 ATSR | 6.5/6.0 kW (230 V) | 168 kg | €2,287.50 |
Safety
- A generator may be connected to the house installation only by an authorised electrician, through a mains/generator changeover switch. Without a changeover switch, current from the generator can flow into the public mains and endanger the people working on it.
- Do not connect a generator to the installation through a socket.
- Run the generator only outdoors, away from windows and doors. The exhaust gases contain carbon monoxide.
Frequently asked questions
How many kW of generator do I need for a home?
For a refrigerator, lighting, router and gas boiler, about 2 kW of rated power is usually enough. With a well pump or air conditioning, count on 5 kW or more, depending on the motor starting surge.
Can I power the whole house with a generator?
You can, but a generator that covers an oven, water heater and air conditioning at the same time is large and expensive. Most customers power only the essential devices and switch off the heating elements while the generator is running.
Is it enough to add up the powers from the plates?
No. To the sum, add the starting surge of the largest motor (pump, refrigerator, air conditioner) and a margin of about 20%, otherwise the generator may stall when the motor starts.
Do I need a three-phase generator?
Only if you have three-phase devices (400 V). For ordinary household loads, a single-phase generator makes better use of its output.
Can I connect a generator to the house installation myself?
No. The connection is made by an authorised electrician, with a mains/generator changeover switch that prevents backfeed into the public mains.
Related
Not sure how much power you need?
Send us a list of devices and the powers from their plates, and we will suggest a model from our range.