The Only Question That Decides Hot Water Or Cold: Is There Grease?

A hot water machine costs considerably more than a cold water one, needs fuel, needs the burner serviced, weighs more and is harder to move around.

For a large share of buyers it is money that would have been better spent on flow rate. For another group it halves their working day. The difference between those two groups comes down to one thing.

The test: is there grease, oil or fat?

That is the whole decision, and it is worth being blunt about it.

Hot water dissolves fats and oils. Cold water at high pressure mostly relocates them.

You can blast a greasy workshop floor with a cold machine at 200 bar for twenty minutes and produce a floor that is wet, smeared and still greasy. Hot water at half the pressure lifts it in a fraction of the time, because the physics is different. Heat reduces the viscosity of the fat and breaks its bond with the surface. Pressure just pushes it about.

If your soiling is greasy, oily or fatty, hot water pays for itself. If it is not, it will not.

Where hot water genuinely earns its cost

Workshops, garages and MOT bays. Engine bays, ramps, floors. Grease is the entire job.

Food production and commercial catering. Fat, protein and a hygiene standard rather than a visual one. Hot water is close to mandatory.

Agriculture and livestock. Organic soiling, fat and protein in parlours, sheds and grain stores. Hot water roughly halves the time and cuts chemical use.

Plant and heavy machinery. Hydraulic fluid, oil, diesel residue baked onto hot surfaces.

Kitchen extraction and ductwork. Not really achievable with cold water at all.

Where cold water is the right answer

Masonry, render and paving. The soiling is organic growth and dirt, not grease. Chemistry plus dwell time does the work, and heat adds nothing.

Fleet and vehicle exteriors. This one surprises people. Traffic film comes off well with cold water plus a suitable traffic film remover and adequate dwell time. Most fleet operations run cold and are right to.

Fencing, decking and general grounds work. Cold water, wide nozzle, appropriate cleaner.

Valeting and detailing. Cold water. You are working near paint, and gentleness matters more than power.

General site and yard cleaning. Cold water and more flow beats hot water and less.

What hot water does not do

Worth saying plainly, because it gets oversold.

It does not clean organic growth faster. Moss, algae and lichen respond to chemistry and dwell time, not heat.

It does not replace the right nozzle or the right chemical. A hot machine used badly still leaves stripes and still damages render.

It does not make a low-flow machine fast. If your problem is that the job takes too long on a large area, the answer is litres per minute, not degrees.

It does not sterilise. Commercial machines typically deliver water well below the temperature and contact time needed for disinfection. Hygiene comes from the chemical and the process.

The running costs nobody mentions at the point of sale

Budget for these before you commit.

Fuel. Diesel or heating oil for the burner, consumed whenever you are running hot.

Burner servicing. An additional annual service item beyond the pump, including nozzle, electrodes and combustion checks.

Descaling. Heating coils scale up, particularly in hard water areas, and a scaled coil loses efficiency and eventually fails. This is the biggest avoidable hot-machine repair cost.

Weight and portability. Hot machines are substantially heavier. If it has to move between sites daily, that is a real operational cost.

Flue and ventilation. Using a hot machine indoors requires proper extraction of combustion gases. This is a safety issue, not a nicety.

The middle option people forget

If you only occasionally need heat, you do not necessarily need a hot machine.

Chemistry plus dwell time closes a lot of the gap on moderate grease. A good degreaser left to work for the time on the label will handle what most people reach for hot water to solve.

A cold machine plus more flow finishes large-area work faster than a hot machine with less flow, on any non-greasy soiling.

Hire for the occasional job. If you need hot water twice a year, hiring is cheaper than owning, servicing and descaling a machine that sits idle.

Frequently asked questions

Do I need a hot water pressure washer?

Only if you are cleaning grease, oil or fat. Hot water dissolves them, while cold water at high pressure mostly moves them around. For workshops, food production, catering, agriculture and plant machinery it pays for itself. For masonry, paving, fencing, vehicle exteriors and general grime, cold water is sufficient.

Does hot water clean better than cold water?

Only on greasy soiling. On organic growth, general dirt and traffic film, chemistry and dwell time do the work and heat adds very little. Hot water solves a specific problem rather than being a straight upgrade.

Is hot water needed for fleet washing?

Usually not. Traffic film and road grime come off well with cold water plus a suitable traffic film remover and enough dwell time. Most fleet operations run cold. Prioritise flow rate instead, because on large vehicles litres per minute decides how long the job takes.

What are the running costs of a hot water pressure washer?

Fuel for the burner, an additional annual burner service covering nozzle, electrodes and combustion, and periodic descaling of the heating coil, which is the largest avoidable repair cost in hard water areas. Hot machines are also heavier to transport and need proper flue arrangements if used indoors.

Can I use hot water in a cold water pressure washer?

That depends on the machine and its maximum inlet temperature, and exceeding it damages seals and the pump. It is a different question from choosing between hot and cold machines, and we cover it separately in its own guide.

The bottom line

Ask whether there is grease. If there is, buy hot and budget for the fuel, the burner service and the descaling. If there is not, buy cold, spend the difference on flow rate and a surface cleaner, and get more done.

RealKleen supplies and services hot and cold water machines from Kränzle, Kärcher, Ehrle and our own range, and has done since 1980. Tell us what you actually clean and we will tell you honestly whether you need heat.