The men is washing his car with hot water pressure washer

Unless you’re a pro that gets paid to power wash don’t buy a hot water power washer.

Why? They’re just too expensive for residential-use. The most affordable one is 1,800 EUR (on-sale). And that’s the 1,200 PSI machine down below.

But if money is no matter and you’re dead-set on a hot water unit then let’s take a look why hot water cleans more, better and quicker.

How Hot Water Pressure Washers Clean Better, Faster

Here’s the deal:

Answering why hot water cleans better than cold water is right up my alley… It’s a simple study in thermodynamics (heat and energy, including internal energy of a system) and kinetics (forces and motion) – both branches of physics. I studied mechanical engineering, which included a few thermo and kinetics courses… But who cares about the equations and fancy terms, let’s just talk about the gist of it:

Hot versus Cold Water

There’s 2 reasons why hot water cleans better than cold water: It has more energy to dislodge the dirt from the surface and it also attracts the dirt away from the surface better when hot. Hot water is a better boxer than cold water – it can easily surround and punch-out then carry away the dirt. Cold water is slower, and not very good at getting in close to Mr. Dirt Stain to land a finishing blow. And in physics terminology:

  1. The higher temperature means the water molecules are on average bouncing around faster – they have more kinetic energy. When introduced to a surface they will quickly bounce around dislodging any weaker molecules such as oil stains or dirt that is on the surface.
  2. The heat increases the internal attractive energy of the water, allowing it to have more attractive force on a microscopic level. Although this energy increase is much less prominent than the increased kinetic energy it still allows improved ability to “suck” away the stain/dirt molecules from the surface.

Soap versus No Soap

Going back to the hot water is a better boxer analogy… Soap would be like allowing the boxer to have a lasso (and he’s a hobbyist cowboy well trained at using it). With it, he quickly loops the rope around Mr. Dirt Stain pulling him in towards his lethal right hook. It’s game over. Dirt Stain has no chance.

Now that you’re starting to realize the benefits of hot water for cleaning, let’s take a look at what a hot water pressure washer is made up of:

Features That Matter


The burner supplies the heat. In the common hot water pressure washers it uses diesel fuel. Kerosene is also common. It has the ability to raise the temperature of the incoming water by 55C. Some machines can even get you a 120C wet steam.

Burner Fuel Tank Size

Take note of the fuel tank size for the burner. It’s usually between 4 and 10 gallons. The bigger the tank the heavier the unit, but also the less often you’ll need to fill it up.

Heating Coil

The heating coil is where the weight of a hot water pressure cleaner comes from. It’s made of schedule 80 pipe or tubing. You can see its mass in this picture. That’s all steel.

Gas or Electric

As with cold water units you either have gas or electric powering the pump. Gas is more affordable if you need more power.

Trailer or Push Cart

The bigger the heating coil, burner, fuel tank and engine the bigger the cart frame needs to be… The biggest are often trailer mounted and are to be pulled from site-to-site by truck. Other come with frames and 4-wheels to push around. And some, like the electric Mini-brute below, just have 2 wheels.

Last update on 2018-11-13 at 00:55 / Affiliate link / Images from Amazon Product Advertising API

Cold Water vs Hot Water Pressure Washers

Smiling men washes his car with cold water pressure washer

Pressure washers can be categorized in several different ways: electric, petrol-powered, residential or professional.

There is also another classification, and that’s cold or hot water pressure washers. Apart from the temperature of water they use, they differ in several other areas as well.

Of course they both have their pros and cons, and knowing more about each will help you make a better decision. Let’s check how they stack up against one another.

Cold Water Pressure Washers

All of the units I have reviewed on my website are cold water units. There are plenty of reasons why they are so popular, but the most important reason is probably that, when compared to their hot water counterparts, they are much cheaper and simpler in their construction (especially electric models).

Also, cold water pressure washers are a lot more practical due to their smaller dimensions which make them easier to move around. As far as maintenance goes even gas-powered pressure washers are a lot easier to maintain than the equivalent hot water designs.

Cold water pressure washers rely on the mechanical force of a pressurized water jet to dislodge dirt from the surface that needs to be cleaned. This force is usually enough to break down most impurities, but they are less efficient when it comes to tackling oily or greasy stains that can be found on hard surfaces such as garage floors, pavements and driveways. The use of detergents helps out a bit on some of the less tough stains, but oil and grease are often too much to handle for most cold pressure washers.

Cold water power washers rely on high-pressure water jets to remove dirt, and the higher the PSI and GPM number, the more powerful the pressure washer is. Hot water pressure washers lose when it comes to the sheer amount of pressure, but they have other strengths. Let’s check them out.

Hot Water Pressure Washers

The best analogy I can come up with to explain the effectiveness of hot water units is washing the dishes. That’s right. Think about it. When you are washing greasy plates you are going to use hot water along with some detergent because it is far more effective than cleaning with cold water. It’s the same when it comes to pressure washers. Yes, but why is hot water more effective? Hold on to your seats because I am going to try and explain some scientific stuff.

For starters we need to look at stuff from a molecular point of view. Water molecules break free from their bonds when heated up to over 100C, that’s how you get steam. It is basically the same with grease and oil molecules. As temperatures rise, their energy levels increase and they can break free from the surfaces they are embedded in. Of course, hot water power washers also use the mechanical force of pressurized water to expel oil and grease particles from the surface. Finally, using soap breaks down the bonds created by grease and oil at a molecular level.

As said, hot water pressure washers have the ability to produce steam which comes in really handy if you want to get surfaces spotless to the point where they’re germ free. However, a hot water and high pressure combo is more effective than just steam. You may also notice that hot water pressure washers have a lower PSI than gas-powered pressure washers.

As far as the cons for hot water pressure washers go? They are big, bulky and thanks to their complex design, more complicated to maintain. They are also more expensive.


Hot Water Pressure Washer
4.3 - votes: 7
So which one to go with? It’s easy. If you don’t have any oil or grease stains to clean save your money and buy a cold water unit. Only if you are dealing with greasy stains often, invest in a hot water pressure washer.

Last update on 2018-11-13 at 00:55 / Affiliate link / Images from Amazon Product Advertising API

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