Hot Water Without a Generator: The Handwash Sink Problem on a Food Truck

Buying Guides & Technical Comparisons Series | SEFFY Mobile Water Systems

The question comes early in the inspection, and it is not about the food. It is about the sink.

Almost every jurisdiction that licenses mobile food vendors expects a handwash sink with hot running water — commonly at or above about 38°C (100°F) — plus soap and single-use towels. Ask a first-time vendor how they plan to meet that requirement and you usually get one of two answers: a kettle on a camping stove, or "it's warm enough in summer".

Neither survives a real service day. And the reason is not laziness. It is that a food truck's electrical system physically cannot heat water, and almost nobody explains why before the truck is built.

This article covers what the requirement actually demands, why the obvious solutions fall short, and how a gas heater that carries its own energy solves it without a generator.

The Requirement, and Why It Is Harder Than It Sounds

Rules differ by country, state and even by city, so treat any figure as a pattern rather than a rule: most licensing regimes require a dedicated handwash sink served by hot and cold running water, with the hot side typically expected to reach around 38°C or above. Some also require a separate three-compartment sink for warewashing, again with hot water. Always confirm the exact standard with your own health authority.

What makes this difficult in a truck is not the water. It is the energy.

A food truck is usually built on a 12V DC system, charged from the vehicle alternator or a small solar array, with perhaps a 1000–2000W inverter for small appliances. That budget is already committed to fridges, lights, a POS terminal, a card reader, a blender, and the exhaust fan. Water heating is not a small appliance. It is the single largest electrical load in any kitchen, domestic or mobile.

The Physics: Why a 12V Socket Can Never Heat Your Water

Heating water follows one equation:

P = ṁ * c * ΔT

where P is heating power in watts, ṁ is mass flow in kg/s, c is the specific heat of water (4,186 J/kg·K), and ΔT is the temperature rise from inlet to outlet.

Take a modest handwash: 3 L/min, with water entering the unit at 15°C and leaving at a comfortable 42°C — a rise of 27K.

P = (3 ÷ 60) * 4,186 * 27 ≈ 5,650 W

So the sink needs about 5.7 kW of heating power.

Now look at what a truck can supply. A 12V circuit at a typical 10A gives you 120W.

To produce 5.7kW from a 12V supply you would need roughly 470 amperes — more than a dozen times the current a truck's wiring, alternator and battery are built to deliver. This is not a matter of buying a better 12V heater. The arithmetic does not close at any price.

So a mobile vendor has only three real options for hot handwash water: boil it, generate electricity to heat it, or burn a fuel that heats it directly.

Why the Obvious Fixes Fall Short

Figure 2. Instant heating replaces the storage tank: no recovery time, no queue while a small electric tank reheats, and no second engine to run.

Boiling water on a stove. It works for one wash. It does not work for the fortieth wash of a lunch service. There is no tap, no temperature control, and a pot of near-boiling water next to a basin is a scald risk. Inspectors also tend to view "we boil a kettle" as an admission that no hot water supply exists.

A generator. A generator can run an electric heater, and that is the traditional answer. It is also heavy, noisy, needs its own fuel, produces exhaust right where you are serving, and adds a second machine to maintain. For a market stall that has to be set up and struck every day, it is a lot of logistics for one sink.

A storage tank. A small electric tank of hot water works until it runs out. Then you wait for it to recover while a queue forms. On a service day, a tank that empties mid-rush is worse than no tank at all.

The Engineering Answer: Carry the Energy, Draw From Any Container

Figure 1. Hot water at the point of use: because the unit heats only the water passing through it, there is no stored tank to run out halfway through a service.

The portable outdoor gas water heater takes the problem off the truck's electrical system entirely. Instead of converting 12V into heat — which the physics above rules out — it burns propane, and carries its own power for the controls in a battery.

That means:

• 10kW of rated heat load, with a hot water capacity of 6 L/min at Δt=25K. Handwash flow is far lower than 6 L/min, so the unit holds a comfortable outlet temperature with margin to spare.
• Outlet temperature adjustable from 35–55°C, so the hot side of the sink can be set where you want it rather than whatever a kettle happens to be.
• A 25W self-priming DC pump across an applicable water pressure range of 0.025–0.4 MPa. It draws straight from a fresh-water container or the truck's own tank and pushes hot water out through the outlet hose to a wash basin. No pressurised line, and no plumbing to install.
• An internal 5200mAh lithium pack (about 3.5 hours to full charge, up to roughly 150 minutes of hot water per charge) running the DC 12V system, so the unit does not need a live connection to the truck's wiring while it works. Charge it before service.
• A maximum gas consumption of 600 g/h, so canister planning is arithmetic rather than guesswork.
• 8.5kg net weight. One person moves it; there is nothing to install and nothing to cut into the truck.

Set-up is a matter of placing the unit, dropping the intake hose into the water container, connecting the gas canister, and running the outlet hose to the basin.

Two Things You Must Do, and One You Must Not Assume

Charge the battery and fill the gas canister before service. Both are required for the unit to start. This is a cordless appliance, not a generator, and it does not produce its own energy. Like any cordless tool, it needs charging in advance.

Run it outdoors or in a thoroughly ventilated exterior area. Combustion produces carbon monoxide — colourless, odourless and toxic. The unit must never be operated inside a sealed truck body, a tent or any enclosed space. On a mobile set-up this normally means placing the heater outside the service area, under the awning or beside the vehicle, and running the outlet hose to the basin.

Do not assume it is a drinking-water appliance. This is a hot-water heater for washing and cleaning. The water it heats is for handwashing and cleaning, not for consumption, and it is not a potable water treatment device.

Field Comparison

Table 1. Four ways to get hot handwash water on a mobile set-up

Read the second row. The 12V column fails on physics, not on quality, and the generator column solves it by adding a second engine to the operation. Gas heating skips the electrical step entirely.

Takeaway for Vendors, Builders and Distributors

For mobile vendors and caterers:

• Confirm your local handwash standard first — the required temperature and sink configuration vary, and it is much cheaper to design for it than to retrofit.
• Do not plan to heat water from the truck's 12V system. At 3 L/min and a 27K rise you need roughly 5.7kW; a 12V circuit at 10A gives about 120W.
• If you go the gas route, treat charging and gas as two consumables to plan every service day. The unit needs a charged battery and a filled canister before it will start.
• Site the heater outdoors or in a ventilated exterior area, and run the outlet to the basin. Never inside the sealed truck body.
• Remember what it is: a hot-water appliance for washing, not a drinking-water source.

For truck builders, converters and distributors:

• Ask the sink question during the spec conversation, not after the build. If a customer expects hot water at the handwash sink, that decision changes the power budget on day one.
• A portable gas heater removes the water-heating load from the electrical design altogether, which simplifies the alternator, battery and inverter sizing you have to quote.
• It also needs no cut-out, no flue aperture and no plumbing, so it can be supplied as an accessory rather than a build option — useful for customers who buy the truck first and the compliance details second.
• Be explicit about the two preconditions (charged battery, filled canister), outdoor-only operation, and the non-potable positioning. Those are the points that prevent both complaints and unsafe use.

Specifications referenced in this article are for the SEFFY Portable Outdoor Gas Water Heater (Thermostatic): rated heat load 10kW; hot water capacity 6 L/min at Δt=25K; maximum temperature rise 55K; outlet temperature adjustable 35–55°C; 25W self-priming DC pump; applicable water pressure range 0.025–0.4 MPa; 5200mAh lithium battery with up to about 150 minutes of runtime per charge, approximately 3.5 hours to full charge; maximum gas consumption 600 g/h; net weight 8.5kg; DC 12V. Heating calculations use the specific heat capacity of water at 4,186 J/kg·K. Food-safety and licensing requirements vary by jurisdiction — confirm the applicable standard with your local health authority.