What size generator do I need for a villa?

It depends mostly on how much air conditioning you want to keep running. Put your loads in above, and use the peak figure rather than the running one.

Why is the peak load so much higher than the running load?

Because motors draw several times their running current for the first moment. A generator sized only for running load will stall when an air conditioner starts.

What is the difference between kW and kVA?

kW is the real work being done. kVA includes current that flows without doing work. Generators are usually rated at 0.8 power factor, so a 20 kVA machine gives about 16 kW.

Can a generator run my air conditioning?

Yes, if it is sized for the starting surge as well as the running load. Inverter units are much gentler to start, so they need less generator than older fixed speed ones.

Is a bigger generator always safer?

No. A diesel engine running at very low load does not reach proper temperature, which causes smoking, glazing and higher maintenance. Right sized beats oversized.

Does UAE heat affect generator output?

Yes. Output falls in high ambient temperatures, which is exactly when demand is highest. Ratings measured in mild conditions are optimistic for a summer here.

Generator Size Calculator

Air conditioners to run

About 1,800 watts each running, much more starting.

Watts per AC unit

Pumps and other motors

Water pump, booster set, lift.

Fridges and freezers

Lighting and sockets

Steady load with no starting surge.

Heaters and other steady loads

Water heater, oven, kettle. Often left off backup.

Motor starting surge

How much extra a motor pulls for the first second.

Power factor

Generators are rated in kVA, which is kW divided by power factor.

Your answer

Generator size

12.2 kVA

Running load is 6.2 kW, but the peak when a motor starts is 9.8 kW.

Running load: 6.15 kW
Peak with starting surge: 9.75 kW
Motor loads: 4.65 kW
Steady loads: 1.5 kW
Largest motor starting: 5.4 kW

Assumes the largest motor starts while everything else is already running, which is the realistic worst case.

Generator Size Calculator for Dubai and the UAE

This tool works out what size generator a property needs. It gives the running load, the peak load and the size in kVA.

The peak is the part that matters. Motors draw several times their running current for the first moment, and a generator sized only for running load will stall when an air conditioner starts.

It is set up for the UAE, where air conditioning is usually the load that decides everything.

Why starting surge decides the size

A motor draws far more current in the first moment than it does once it is turning. Several times more.

On the mains supply this does not matter much, because the grid is enormous and does not notice. A generator is not enormous, and it does notice.

If a generator is sized for the running total, then the moment an air conditioner compressor starts, the demand jumps well past what the generator can produce. The voltage sags, the engine labours, and either it recovers badly or it stalls.

So the generator has to be sized for the running load plus the extra that the largest motor needs while it starts.

That is why the peak figure in this tool is much higher than the running figure, and it is the number to buy against.

kW and kVA are not the same

Generators are sold in kVA. Appliances are labelled in kW or watts. They are related but not equal.

kW is real power, the work actually being done. kVA is apparent power, which includes the current that goes back and forth without doing work.

Power factor is the link. kVA is kW divided by power factor.

Generators are normally rated at 0.8 power factor. So a 20 kVA generator can deliver about 16 kW of real power.

This catches people out. Somebody works out they need 16 kW, buys a 16 kVA generator, and finds it delivers only around 13 kW. The tool gives both figures so that does not happen.

Deciding what actually goes on backup

The cheapest way to size a generator is to be honest about what really needs to keep running.

Air conditioning
In this climate this is not a luxury during a long outage. But cooling one or two rooms rather than the whole property changes the generator size dramatically.
The water pump
Without it there is no water above ground floor. Small load, large consequence, and it is a motor so it brings a surge.
Fridges and freezers
Small and worth keeping. Food spoils quickly here.
Lighting and sockets
Cheap to include and the thing people notice first.
Water heaters
Usually left off. They are large, and in this climate you can manage without hot water for a few hours.
Ovens and dryers
Almost always left off. Very large loads for things that can wait.

Oversizing has its own problems

Having decided to size for the surge, it is tempting to add more on top for comfort. That causes different trouble.

A diesel generator running at a small fraction of its rated load does not run cleanly. The engine does not reach proper operating temperature, unburnt fuel builds up in the exhaust, and the cylinders glaze over time.

The result is a generator that smokes, needs more maintenance and delivers less than it should when it is finally asked for real output.

It also costs more to buy, more to install, takes more space and uses more fuel at idle.

The right target is a generator that runs at a healthy proportion of its rating during normal use, with enough headroom to absorb the starting surge without stalling.

If the surge is the only reason a much larger generator is needed, soft starters on the motors are often a cheaper answer than a bigger machine.

What else matters in the UAE

Sizing is the start. These decide whether it works when you need it.

Heat derating
A generator produces less in high ambient temperatures. A rating measured in mild conditions is optimistic for a UAE summer, which is exactly when you need it.
Dust
Air filters clog far faster here. A generator that sits unused for months can have a blocked filter before it has run an hour.
Ventilation
An engine in an enclosed hot room needs a lot of air, both to breathe and to carry heat away.
Fuel storage
Diesel degrades over time, especially in heat. Fuel that has sat for a year is not the fuel you want in an emergency.
Exercise it
A standby generator should be run under load regularly. Most failures are found at the moment of need, in a machine nobody had started for months.
Exhaust and noise
Both need planning, and in a residential area both are usually what the neighbours notice first.

Questions people ask

What size generator do I need for a villa?: It depends mostly on how much air conditioning you want to keep running. Put your loads in above, and use the peak figure rather than the running one.
Why is the peak load so much higher than the running load?: Because motors draw several times their running current for the first moment. A generator sized only for running load will stall when an air conditioner starts.
What is the difference between kW and kVA?: kW is the real work being done. kVA includes current that flows without doing work. Generators are usually rated at 0.8 power factor, so a 20 kVA machine gives about 16 kW.
Can a generator run my air conditioning?: Yes, if it is sized for the starting surge as well as the running load. Inverter units are much gentler to start, so they need less generator than older fixed speed ones.
Is a bigger generator always safer?: No. A diesel engine running at very low load does not reach proper temperature, which causes smoking, glazing and higher maintenance. Right sized beats oversized.
Does UAE heat affect generator output?: Yes. Output falls in high ambient temperatures, which is exactly when demand is highest. Ratings measured in mild conditions are optimistic for a summer here.

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