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Updated October 2026. Specs come from manufacturer and dealer listings checked in October 2026.
A hot water heater for a pressure washer turns a cold machine into a grease-cutting tool. You have two ways to get there: add a burner “hot box” to the cold water rig you already own, or buy a hot water pressure washer with the burner built in. This guide shows which one fits your work, how to size the heater to your GPM, and which models pros actually shop for.
Short version: if most of your work is houses, roofs and concrete, you probably don’t need hot water. If you clean restaurants, dumpster pads, gas stations, fleets or heavy equipment, hot water pays for itself in time saved.
Quick picks
| Best for | Model | Key specs |
|---|---|---|
| Best all-in-one hot water unit | Mi-T-M HSP-3504-3MGH | 3,500 PSI, 3.3 GPM, Honda GX390, diesel or kerosene burner |
| Best add-on for 8–10 GPM rigs | BE 12VDC diesel-fired hot box (99012V) | 8–10 GPM, 420,000 BTU, 200°F max, 7 gal tank |
| Best add-on for 4–5 GPM machines | BE 115V diesel-fired hot box (96115V) | 4–5 GPM, 200°F max, 115V plug-in, 7 gal tank |
| Best electric hot water unit on Amazon | NorthStar Wet Steam/Hot Water, 230V | 2,750 PSI, 2.5 GPM, 150°F temperature rise, 250°F wet steam |
Do you need hot water?
Heat melts grease, oil and gum so detergent and pressure can lift them. Cold water just pushes them around. Mi-T-M, which builds both types, recommends cold water for siding, decks, driveways and vehicles, and hot water for oil, grease, big equipment and food-industry sanitation (Mi-T-M).
| Job | Cold water | Hot water |
|---|---|---|
| House washing, roofs (soft wash) | Yes | Not needed |
| Driveways, sidewalks, patios | Yes | Helps with oil stains |
| Restaurant dumpster pads and drive-thrus | Slow | Yes |
| Gas stations and parking garages | Slow | Yes |
| Fleet trucks and heavy equipment | Slow on grease | Yes |
| Gum removal | Very slow | Yes (wet steam is best) |
A useful bonus: most hot water units still run as cold water machines with the burner off, so one rig can cover both kinds of work.
Hot box vs hot water pressure washer
There are three ways to put hot water through your wand.
1. Add-on hot box (burner module)
A hot box is a diesel-fired heating coil in a frame. Water leaves your existing pump, runs through the coil and comes out hot. You keep the machine you have and add heat. It’s the most common upgrade for trailer rigs that already run 8 GPM or more.
The catch is matching. Each hot box is rated for a flow range, and it needs power for the burner (12V from a battery or a 115V outlet, depending on the model). Run too little flow through it and it can overheat; run too much and the temperature rise drops.
2. All-in-one hot water pressure washer
The pump, engine, burner and fuel tank come as one unit with matched parts and one warranty. It’s simpler to set up and service, and it’s the usual choice for a dedicated commercial or fleet truck.
3. Electric hot water units
Electric-pump units with an oil or diesel burner suit shops and wash bays where you have 230V power. The burner still makes exhaust, so it needs ventilation.
What about a home water heater tank?
Some DIY threads feed a cold machine from a tank water heater. It works for light use, but check your pump’s maximum inlet temperature first. Many pumps limit inlet water to around 140°F, and the tank runs cold fast at 4 GPM. For paid work, a burner is the reliable option.
How to size a hot water heater (BTU by GPM)
Heating water takes about 1 BTU per pound per degree, and a gallon of water weighs 8.33 pounds. So the heat you need per hour is:
BTU per hour = GPM × 8.33 × 60 × temperature rise (°F)
Burners aren’t 100% efficient, so add about 20–25% to that number for the burner rating. To raise 40°F well water to 180°F (a 140°F rise):
| Flow | Heat needed (output) | Burner rating at ~80% efficiency |
|---|---|---|
| 3 GPM | ~210,000 BTU/hr | ~262,000 BTU/hr |
| 4 GPM | ~280,000 BTU/hr | ~350,000 BTU/hr |
| 5 GPM | ~350,000 BTU/hr | ~437,000 BTU/hr |
| 8 GPM | ~560,000 BTU/hr | ~700,000 BTU/hr |
| 10 GPM | ~700,000 BTU/hr | ~875,000 BTU/hr |
This is why high-flow hot boxes don’t heat as much as small units. A 420,000 BTU burner at 10 GPM gives roughly an 80°F rise, which is still plenty for grease when your incoming water isn’t ice cold. If you need very hot water at high flow, look for a bigger burner or run two heaters.
The best hot water heaters and units for pros
Mi-T-M HSP-3504-3MGH: best all-in-one hot water unit
- 3,500 PSI, 3.3 GPM, Honda GX390 gas engine
- Diesel or kerosene burner, 12V ignition
- Seen at about $5,320 at an online dealer in October 2026
A complete gas-powered hot water machine for crews that work away from power outlets. It’s also our hot water pick in the best commercial pressure washer guide. Sold through Mi-T-M dealers and industrial suppliers.
BE 12VDC 8–10 GPM diesel-fired hot box (99012V): best add-on for trailer rigs
- Rated for 8.0–10.0 GPM, 200°F max water temperature
- 420,000 BTU diesel burner, 12VDC electronic ignition
- 260 ft schedule 80 steel coil, 7 gallon fuel tank, about 545 lb
Built to pair with the 8–10 GPM belt-drive machines that many trailer and skid setups use (BE Power Equipment). Runs off your trailer battery, so no generator is needed for the burner. Plan for the weight; see our pressure washer trailer setup guide.
BE 115V 4–5 GPM diesel-fired hot box (96115V): best add-on for 4 GPM machines
- Rated for 4.0–5.0 GPM, 200°F max
- 115V, 15A with a 35 ft GFCI cord
- 147 ft coil, 7 gallon tank, about 365 lb; 3-year burner and lifetime coil warranty listed
A match for the 4,000 PSI, 4 GPM cold machines most owner-operators start with (BE Power Equipment). It needs a 115V outlet or generator for the burner.
NorthStar Wet Steam/Hot Water, 230V: best electric hot water unit on Amazon
- 2,750 PSI, 2.5 GPM, 230V electric motor
- 150°F temperature rise; switches to 250°F wet steam
- Total Start/Stop: the motor runs only when you pull the trigger
Lower flow than a gas rig, but the wet steam mode is useful for gum and greasy equipment in a shop or wash bay.
Gear rated for hot water
Standard hoses, guns and quick-connects are often rated for cold water only. Hot water softens them and can make them burst. Before you add heat, check that everything after the heater is rated for your top temperature.
- Hot water hose: NorthStar 6,000 PSI, 50 ft x 3/8 in., wire-braided and rated for hot water. Check price on Amazon
- Hot water gun and lance: NorthStar vented gun rated up to 5,000 PSI at 300°F. Check price on Amazon
- Hose reel: pick one with a swivel rated for hot water. See our pressure washer hose reel picks.
Safety: burns, exhaust and fuel
- Burns: 200°F water and wet steam scald in a second. Wear gloves and long sleeves, and never point the wand at people.
- Carbon monoxide: diesel burners and gas engines make exhaust. Never run them in a closed garage or wash bay without ventilation.
- Fuel: refuel with the burner off and cool. Use the fuel the manufacturer lists (usually diesel or kerosene, never gasoline in the burner).
- Water first: never fire the burner without water flowing through the coil.
- Winter: drain the coil and protect the pump when temperatures drop. Our equipment list covers pump antifreeze.
What hot water work pays
Hot water opens commercial work that residential crews can’t do well: restaurant pads, fleets, gas stations and parking garages. These jobs are often recurring monthly or quarterly. Commercial crews often bill $100–$200 per hour, according to our pressure washing price guide. Add your fuel cost per hour when you quote, and use the pressure washing estimate calculator for flatwork.
Recurring commercial accounts are easier to manage with scheduling software that handles repeat visits and invoices.
How we compared
We didn’t test these machines ourselves. We compared manufacturer specs (flow range, BTU, maximum temperature, power needs, weight and warranty), dealer prices seen in October 2026, and how well each option fits the rigs our readers already own. We calculated the BTU table from the standard heating formula for water. Always confirm specs with the dealer before you buy.
Related guides
- Best commercial pressure washer (4,000 PSI picks)
- Pressure washer trailer setup
- Pressure washing equipment list
- Best surface cleaner
- How much to charge for pressure washing
Frequently asked questions
Can you add a hot water heater to a cold pressure washer?
Yes. An add-on hot box connects after your pump’s outlet. Match its GPM range to your machine, make sure it gets the power it needs (12V or 115V), and use hoses and guns rated for hot water.
How hot does a hot water pressure washer get?
Most burner units reach about 200°F at the gun. Wet steam models go higher; the NorthStar 230V unit lists 250°F in steam mode.
How many BTU do I need for a 4 GPM pressure washer?
About 280,000 BTU per hour of heat for a 140°F rise, or roughly 350,000 BTU as a burner rating once you allow for efficiency losses.
Is a hot water pressure washer worth it?
It’s worth it if you clean grease, oil or gum regularly, or want restaurant, fleet and gas station accounts. For houses, roofs and concrete, a cold water machine and a soft wash setup cover most work.
Can I use a hot water pressure washer with cold water?
Yes. Most units run as cold water machines with the burner switched off.
What fuel does a pressure washer burner use?
Most use diesel or kerosene. Check your model’s manual, and never put gasoline in the burner tank.
