Petrol vs Diesel Generators: Which Is Better for Construction Sites?

Quick answer

Key differences at a glance

Fuel safety and storage

Petrol gives off flammable vapour at normal temperatures, so it catches fire far more easily than diesel. That makes diesel the safer fuel to store and handle on a busy site.

Storing petrol on site

Storing and using petrol at work is covered by the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR). You must assess the risks and keep them as low as possible. HSE guidance says work containers must be UN approved for petrol. Read the HSE guidance on petrol in the workplace.

Storing diesel on site

In England, above-ground oil containers of more than 200 litres at business premises fall under the Control of Pollution (Oil Storage) (England) Regulations 2001. The secondary containment, such as a bund, must hold at least 110% of the container's capacity. Read the Oil Storage Regulations.

Refuelling safely

Switch the generator off and let it cool before refuelling, whichever fuel it uses. Never overfill the tank, wipe up any spills, and keep naked flames and other ignition sources away.

Red diesel rules for generators

Construction lost its entitlement to red diesel from 1 April 2022, so diesel generators on construction sites generally need to run on standard (white) diesel. Some sectors, such as agriculture, kept their entitlement. Check the current HMRC guidance if you are unsure whether your use qualifies.

Running costs and fuel use

Diesel engines generally use less fuel than petrol engines to do the same amount of work, which matters most on long shifts. Petrol generators usually cost less to buy, so they often work out cheaper for short or occasional jobs.

Whichever you choose, size the generator correctly. A generator that is far too big burns fuel for capacity you never use, and one that is too small runs flat out and works harder. Our guide, What Size Generator Do I Need?, shows how to work out your load.

Noise

A silenced cabinet encloses the engine, but that does not always make a diesel generator quieter than a petrol one. Compare the published guaranteed sound power level (LwA) for each model.

If noise is your main concern, near homes, schools or events, look at a silent inverter generator. Read our guide, What Is an Inverter Generator?

Weight and moving it

Small petrol generators sit in a tubular frame and can be lifted by two people. The SIP Medusa T2500W, for example, weighs 37kg. Larger petrol models add wheels and handles.

Diesel generators are much heavier. The SIP Medusa T5500 diesel weighs 156.6kg on four wheels, and the T15000 three phase weighs 291kg on castors, with a lifting eye for a crane or hoist. Plan lifts under the Manual Handling Operations Regulations, and use lifting equipment for heavy units.

Maintenance

Choose a fuel type to see the service intervals from the SIP user manuals.

Intervals from the SIP Medusa T2500W, T3000W and T5500W manuals (petrol), and the T5500 and T15000 manuals (diesel). On the T15000, keep loads under 50% for the first 20 hours. Always follow the manual for your model.

Which suits your job?

Pick what matters most on your job.

Our SIP Medusa petrol and diesel generators

Petrol and diesel range compared

Filter by fuel, or click a column heading to sort.

Figures from SIP product data, user manuals and Declarations of Conformity. Check each product page for full specifications.

Frequently asked questions

Which is better, a petrol or diesel generator?

It depends on the job. Petrol generators are lighter, cheaper to buy and suit short jobs and small works. Diesel generators suit full shifts, standby power and three phase machinery, and diesel is safer to store.

Are diesel generators more fuel efficient than petrol?

Diesel engines generally use less fuel than petrol engines for the same amount of work. The saving matters most on long shifts and heavy loads. For short or occasional jobs, a petrol generator's lower purchase price often outweighs it.

Can you use red diesel in a generator on a construction site?

Construction lost its entitlement to red diesel from 1 April 2022, so site generators generally need standard diesel. Some sectors, such as agriculture, kept their entitlement. Check HMRC's guidance if you are unsure.

Are diesel generators quieter than petrol generators?

Not always. A silenced cabinet encloses the engine, but the published sound power level is what to compare. For example, the SIP Medusa T5500 diesel is 97dB(A) and the T5500W petrol is 96dB(A). For the quietest running, look at a silent inverter generator.

Is it safer to store diesel or petrol on site?

Diesel, because it is much less flammable than petrol. Petrol storage at work falls under DSEAR and needs UN approved containers. In England, diesel containers over 200 litres at business premises need secondary containment holding at least 110% of the container's capacity.

Do I need a diesel generator for three phase power?

In our range, yes. The SIP Medusa T15000 is a three phase silenced diesel generator with 400V and 230V outlets and an 11kW rated output. Our petrol generators are single phase.

How often does a diesel generator need servicing?

For the SIP Medusa T5500 diesel, change the oil and oil filter after the first month or 20 hours, then the oil every 3 months or 100 hours. Change the oil filter and air filter every 6 months or 300 hours. Always follow the manual for your model.

Which petrol generator runs 110V site tools?

The SIP Medusa T3000W gives 1750W at 110V from a 16A socket, and the T5500W gives 3000W at 110V from a 32A socket. Both use a selector switch, so 110V and 230V are not live at the same time. The T2500W is 230V only.