Ask anyone who has owned both machines. They will tell you a hot water machine is twice the machine.
That is true. What they leave out is the other half of it. A burner is a standing cost, and it runs whether you are earning or not.
Already know which machine suits your work? Our hot water and cold water comparison covers that ground.
This page is about the money. What heat costs per hour, what it saves per hour, and which side of that line your work falls on.
What the heat is actually doing
Heat is not more power. Pressure and flow do the mechanical work, and adding a burner changes neither.
What heat changes is chemistry. Fats, oils and greases soften as the temperature rises. A film of cooking fat runs off at 60 degrees, where a cold jet only polishes it.
Detergents gain the same way. Most surfactants work faster when warm, so you use less product and wait less time for it to bite.
So here is the honest description of a hot machine. It does not clean harder. It cleans faster, and only on the right sort of dirt.
The three jobs where heat always wins
Anything greasy. Kitchen extraction, food production floors, butchery and takeaway yards. Plant and machinery, engine bays, workshop floors soaked in years of oil.
Cold water and a strong degreaser will get there in the end. Hot water gets there in a third of the time.
Anything that has to be sanitary. Dairy, food preparation, animal housing and veterinary work. Here heat is part of the specification, not a convenience.
Anything with a tight window. Picture a commercial kitchen cleaned between closing and opening, or a production line during a shift changeover. The hours you save are the whole point.
The jobs where it is money burning
Patios, driveways and block paving. The dirt is biological and mineral, not fatty. Heat adds very little, and the right technique with a cold machine gets a better result anyway.
Car washing and detailing. Almost the whole detailing trade runs cold, and that is no accident. Snow foam and cold water do the job without risking trim, wraps and sealants.
General site and fleet washing. Road film, mud and dust all come off cold. Unless you are facing a diesel spill or heavy oil, the burner costs you fuel for no gain.
Occasional use. A burner that runs a few hours a month still needs its annual service, and the coil still scales up. Low use is the worst case, because the fixed costs land regardless.
What heat actually costs to run
Four costs, and only one of them is the purchase price.
The machine. A hot water machine is a substantial step up over a cold machine of the same pressure and flow. You are buying a burner, a coil, a fuel system and the controls to manage them.
Fuel. A diesel-fired machine burns roughly four to six litres an hour with the burner running. Check the figure for your own model first.
Then multiply by the hours the burner will be lit, not the hours the machine is switched on. Most operators overestimate that second number badly.
Servicing. This is the cost people forget. Our full workshop service is £169 including VAT for a cold water machine. A hot machine with descaling is £279.
The difference is the burner, the coil and the descaling work, and it repeats every year.
Scale. In a hard water area, scale builds on the heating coil and inside the pump. Left alone, it restricts flow and eventually cooks the coil. Descaling keeps your most expensive component alive.
The back of an envelope
Here is the sum, and it takes about a minute.
- Work out your hourly rate, or what an hour of your own time is worth if you hold the lance
- Estimate the hours heat saves you each week, on the jobs where it genuinely helps
- Multiply. That is your weekly gain
- Add up the extra cost. Fuel for those hours, the annual servicing difference, and the purchase premium across the life of the machine
- Compare the two numbers
Is the gain clearly bigger? Buy hot and stop thinking about it.
Are the two close? Buy cold, and spend the difference on better chemical, a surface cleaner and a second lance.
The pattern we see is simple. Heat pays when labour is your highest cost and grease is your main enemy. Where either of those is untrue, it does not.
What you need in place before a hot machine arrives
Buying is the easy part. Hot water machines carry requirements that cold machines do not.
Ventilation and flue. A diesel burner produces exhaust gas, so it cannot run in an enclosed space without proper extraction.
Stuck with an indoor site? Look at an electrically heated machine instead. That removes the combustion problem and brings a different one, which is the electrical supply it needs.
Fuel storage. Diesel on site means a compliant container and somewhere sensible to keep it.
Electrical supply. Hot machines draw more, and some of them are three-phase. Sort this out before you order, not after. We have written about why the plug does not fit more than once, because it keeps happening.
Frost protection. A coil full of water that freezes makes for a bad morning. Hot machines hold water in more places than cold ones, so the winter routine matters more, not less.
Frequently asked questions
Is a hot water pressure washer worth it?
It depends entirely on the dirt. Does your work involve grease, oil, fat or sanitising? Heat will often halve your cleaning time, and it pays for itself quickly.
Do you clean patios, vehicles, mud and road film? Heat adds cost without adding much result, and a better cold machine is the smarter purchase.
How much diesel does a hot water pressure washer use?
Most diesel-fired machines use four to six litres an hour while the burner is firing. The exact figure varies by model and by the temperature you are running.
The number that matters is burner hours, not machine hours. The burner cycles off whenever you are not calling for heat.
Why does servicing a hot water pressure washer cost more?
Because there is more to service. A hot machine needs burner setup, coil inspection and descaling on top of the usual pump work.
Our cold water full workshop service is £169 including VAT, and the hot water equivalent with descaling is £279.
Can I use a hot water pressure washer indoors?
Not a diesel-fired one, unless there is proper flue extraction, because it produces combustion exhaust.
For indoor work, an electrically heated machine removes the exhaust problem. Check the electrical supply it needs before ordering.
Does hot water damage paintwork or trim?
It can, which is why the detailing trade largely runs cold. Heat softens sealants, waxes and some plastics and adhesives, and it raises the risk on vinyl wraps.
For vehicle work, cold water and good chemistry give a safer finish, and it usually looks better too.
The bottom line
Heat is a tool for one specific problem, and that problem is grease under time pressure.
Work out what an hour of your time is worth. Be honest about the hours heat will really save you. Then put the fuel and the annual descaling on the other side of the page.
The answer falls out in about a minute.
Kränzle UK sells both machines and services, so we have no reason to push you either way. Call us with the jobs you actually do, and we will tell you which one you need. Better still, speak to us first, before you spend the extra.