Hot Boxes: Add Hot Water to the Machine You Already Own

Grease barely moves for cold water. Heat it to 180 degrees and it lets go, which is why hot water crews clean dumpster pads and drive-thrus in half the time. A hot box bolts hot water capability onto the cold machine you already own instead of making you buy a whole new rig. Sun Brite Supply sizes and stocks hot boxes in Gaithersburg, MD. Call 301-519-9274 with your machine's GPM and we will match a unit to it.

How a Pressure Washer Hot Box Works

A hot box is a diesel-fired water heater that sits inline between your pump and your gun. High pressure water from the pump enters the unit, winds through a steel heating coil wrapped around a burner flame, and comes out the other side hot. A flow switch fires the burner only when you pull the trigger, and a pressure relief valve plus a rupture disc protect the coil if something blocks flow. Your engine, pump, and unloader stay exactly as they are. That is the whole appeal: one jumper hose in, one hose out, and your cold machine washes hot.

Picking the Right Hot Box

Match the flow rating to your pump

Temperature rise depends on how fast water moves through the coil. Push 8 GPM through a unit rated for 4 and you get lukewarm water and a disappointed customer. Run 3 GPM through an 8 GPM box and you get plenty of heat with capacity to spare. Buy the box rated at or above your pump's flow, and remember that a unit with headroom lets you upgrade the machine later without replacing the heater.

12V or 115V burner power

The burner needs electricity for the fuel pump, blower, and ignitor even though the heat comes from diesel. A 12V unit runs off a battery and your engine's charging system, which suits trucks and trailers working away from outlets. A 115V unit plugs into shore power or a generator, which suits stationary wash bays and shops. Same heat either way. Choose based on where the unit will live.

Stationary or portable

Skid and truck rigs want a compact vertical unit plumbed in permanently. Wash bays and plants often do better with a stationary hot box mounted on the wall near the bay, fed by whichever machine is running that day.

Hot Boxes and Burner Ignitors We Carry

Ignitors move fast and availability changes, so call before you drive out for one. We can also cross-reference your burner model if the part number tag is long gone.

From the Field

Most "dead hot box" calls we take are not dead hot boxes. In cold weather it is usually fuel: summer diesel gels, filters clog, and the burner starves. In every season the next suspects are the ignitor and the electrodes, which is why we keep Beckett and Wayne ignitors on the shelf list. If the burner runs but the water is only warm, check the fuel nozzle and pressure before blaming the coil, since a worn nozzle underfires the burner. And descale the coil once a year on Maryland well water. Scale inside the coil steals heat first and plugs the coil second, and a coil is the most expensive part on the unit.

Related Collections

• Burner parts and burner nozzles
• Ignitors and transformers
• Fuel nozzles, fuel pumps, and fuel filters
• Thermostats for temperature control
• Hot water pressure washers and hot water skids
• Hot water and steam hoses
• Lances rated for hot water
• Degreasers to pair with the heat
• See it running at our Gaithersburg store

Frequently Asked Questions

Will a hot box work with any cold water pressure washer?

Almost any gas or electric machine works as long as the hot box is rated for your pump's GPM and PSI. It installs downstream of the pump, so the pump itself never sees hot water and needs no changes.

How hot does the water get?

Most units adjust up to about 200 degrees F at the gun. Actual temperature depends on flow. Less GPM through the coil means a bigger temperature rise, so the same box runs hotter on a 4 GPM machine than on an 8 GPM machine.

What fuel does a hot box burn?

Diesel or kerosene fires the burner. The 12V or 115V electrical side only powers the fuel pump, blower, and ignitor. Expect roughly a gallon of fuel or more per hour of trigger time depending on burner size.

Why would I pick a 12V hot box over a 115V unit?

Pick 12V for trucks and trailers that work away from outlets, since it runs off a battery and the engine's charging system. Pick 115V when you have shore power, a generator, or a fixed wash bay.

My burner clicks but will not light. What do I check?

Start with fuel level and the fuel filter, then the ignitor and electrode gap, then the fuel nozzle. Ignitors are a common wear part and cost far less than a service call. Bring yours in and we will bench check it.

Is a hot box cheaper than buying a hot water machine?

Usually, if your cold machine is healthy. A hot box costs around $4,000 while a comparable hot water rig costs a good deal more, and the box can outlive the machine and move to the next one. If your cold unit is tired, put the money toward a complete hot rig instead.