Article: Hot Water on the Road: The Highland Rigs Guide to Van Water Heaters

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Oct 20, 2026

Hot Water on the Road: The Highland Rigs Guide to Van Water Heaters

There's a moment on every good trip when a hot rinse at the end of the day turns your van from a vehicle into a home. It's also one of the first systems we talk through with clients at Highland Rigs when we're laying out a Mercedes Sprinter conversion: which kind of water heater, how big, how it gets its power, and where it lives in the build.

To put this guide together, we worked through the full series on van water heating from our friends at GoCode Overland and combined their research with how we approach hot water in Highland Rigs builds. Every source is linked so you can dig deeper.

The Four Ways a Van Makes Hot Water

Almost every van water setup falls into one of four categories, as GoCode lays out in its complete guide to hot water for van life:

Electric storage boilers – a small insulated tank heated by a 12V and/or 110V element.
Propane tankless units – heat water on demand, but require a propane system and outside venting.
Engine-coolant systems – borrow waste heat from your engine while you drive, usually with an electric backup.
Diesel or hydronic combos – share heat with the cabin heater you may already be running.

None of these is the universal winner. At Highland Rigs, the right answer depends on the client's electrical system, climate, and how they actually travel, which is why we start every conversation with those questions instead of a product name.

Start With Your Power System, Not the Heater

The most useful advice in the whole GoCode series is to size the water heater to your electrical system rather than the other way around (Choosing the Right Water Heater).

Here's the math GoCode walks through in Running a Water Heater on Lithium and Solar: a 200W element on a 12V system pulls about 16–17 amps. Running it for roughly an hour to heat a 6-liter tank is a reasonable load on a 200–400Ah lithium bank, especially with 300–600W of solar on the roof. A 750–1200W element is a very different story — that's 60 to 100+ amps through an inverter, which isn't something you want running for long without shore power or a generator.

A few habits make the numbers work even better:

Heat water during peak sun so you're spending solar you're already making.
Choose a well-insulated tank so it holds heat between uses.
Pair a modest tank with a low-flow shower head instead of buying a bigger, thirstier unit.

When Highland Rigs designs an electrical system, the water heater goes into the load calculation on day one, right alongside the fridge, lights, and water pump. GoCode makes the same point in Power, Batteries & Off-Grid Water Heating: "free" heat from the engine or a diesel heater only shows up when you're driving or when it's cold, so some electric backup is still worth having.

12V, 110V, or Both?

According to GoCode's 12V vs 110V breakdown, a 12V element (often in the 180–200W range) runs straight off your batteries and works anywhere, but heats slowly — better for small, frequent top-ups. A 110V element, commonly 500W or more, heats much faster but needs shore power or a hefty pull through your inverter.

Dual-voltage units let you use whichever makes sense: 110V when you're plugged in at a campground, 12V when you're boondocking. For Highland Rigs clients who split time between hookups and off-grid stays, dual-voltage is usually the most flexible choice. Strictly off-grid weekenders with a smaller battery bank can keep it simple with 12V only.

Electric vs. Propane

GoCode's honest breakdown of electric vs. propane comes down to what's already on board:

Propane tankless gives you continuous hot water with very little electrical draw, but you're adding a tank, regulator, gas lines, exterior venting, and refills.
Electric storage skips combustion and exhaust entirely and installs with just power and plumbing, but you're limited to the tank's capacity.

If a Highland Rigs build isn't already carrying propane for cooking, we generally lean electric — it's simpler to install, simpler to live with, and fits the all-electric direction most modern Sprinter builds are heading.

How Much Hot Water Do You Really Need?

Probably less than you think. GoCode's hot water sizing guide estimates that a solo traveler uses about 2–3 gallons of total water a day when showering at gyms or campgrounds, and closer to 4–6 gallons when showering in the van.

The bigger lever is the shower head. A five-minute shower at a standard flow rate can use around 10 gallons, while a low-flow head with stop-and-soap habits can bring that down to 1.5–2 gallons. Compact 3–6 liter boilers (about 0.8–1.6 gallons) also stretch further than their size suggests because the hot water is blended with cold at the tap.

Rough sizing from the GoCode series (Pundmann review):

3L – minimal hot water use or very tight cabinet space
6L – a comfortable middle ground for most solo travelers and couples
9–10L – two people showering daily, or anyone who wants more buffer

One point we hammer home at Highland Rigs: physical footprint matters as much as capacity. As GoCode notes in its complete guide, a tall cylindrical tank can eat more usable cabinet space than a rectangular unit holding a similar amount of water. Measure the space before you commit. GoCode also offers a water heater calculator if you want to run your own numbers.

Already Running a Diesel Heater? Consider a Combo

Many Highland Rigs clients add a diesel parking heater like a Webasto or Autoterm for cold-weather comfort. As GoCode explains in Diesel Air Heater + Hot Water Combos, a combo water heater taps that same heat through an exchanger, so your water warms up as a side effect of heating the cabin.

It shines in builds that see regular cold weather. If you mostly travel in mild climates, the benefit is small. Either way, you'll still want an electric element for warm-weather trips, and the install is more involved than a standalone boiler — so we plan it at the same time as the heater, not as an add-on later.

A Highland Rigs Favorite: Rixen Hydronic Heating

If sharing heat between your cabin heater and your water appeals to you, there's a more complete version of that idea that many Highland Rigs customers choose: a hydronic system from Rixen's.

Instead of keeping a small tank of water hot, a Rixen system heats a closed loop of coolant (glycol) and runs it through a heat exchanger. Your fresh water picks up that heat as it flows to the faucet or shower, so you get hot water on demand. In other words, it works as a tankless hot water option: you aren't limited by a 6- or 10-liter reservoir, and back-to-back showers don't drain your supply.

What a Rixen system does

Two jobs in one system. The same setup handles cabin heat and hot water. One retailer lists Rixen's MCS6 kit with an S-3 diesel furnace at up to 17,000 BTU of heat along with continuous on-demand hot water (Vanland Store).
Several heat sources. The diesel burner does most of the work, but the system can also tie into your van's engine coolant so you're heating while you drive, and can preheat the engine for easier cold starts. Some setups add a 120V element that heats the loop when you're on shore power (RoamRig).
Light on your batteries. Because diesel supplies the heat, the electrical draw is small: the MCS6 kit is listed at roughly 32–50 watts depending on the pump, with fuel use around 0.15 gallons per hour (Vanland Store).
Room to grow. Options like extra air vents and radiant floor heat can be added to the same loop.

Rixen's is a family-owned company founded in 1985 in the Pacific Northwest and is an Eberspaecher distributor that builds its own heating systems (Overland Expo). It also offers the MCS One, an all-in-one box that combines the furnace and water heating components to simplify installation (RV News).

Why it's a common route for Highland Rigs customers

Our Sprinter clients tend to travel year-round, chase cold-weather trips, and want hot water that keeps up with real showers. A Rixen hydronic system fits that well: it draws from the same diesel the Sprinter already runs on, keeps the cabin warm, and delivers hot water without asking much of the battery bank.

The tradeoffs

Cost. It's a bigger investment than a compact electric boiler; the MCS6 kit was listed at roughly $5,200–$6,600 at the time of writing, before installation, and prices change.
Install complexity. Coolant loops, a furnace, exhaust, fuel lines, and a heat exchanger make this a professional-level install that needs to be planned into the layout from the start.
Overkill for mild climates. If you rarely need cabin heat, a simple electric storage heater may serve you better.

At Highland Rigs, we design the Rixen loop, plumbing, and electrical together during the layout phase so everything fits cleanly and stays serviceable.

Brand Snapshot: Pundmann, Isotemp, and Duoetto

GoCode compares the three names that come up most for van builders in Pundmann vs Isotemp vs Duoetto and its brand comparison overview:

Isotemp – Marine heritage and a long track record, built around engine-coolant heating with an electric backup. The electric element draws 750–1200W, and the cylindrical tank needs more cabinet depth.
Pundmann – A German maker of compact rectangular boilers (roughly 9" x 15" x 8" depending on model) with low-draw 180–200W elements, offered in 3L, 6L, and 9L sizes plus a 10L Air Flow Heat model that can tie into a diesel heater. GoCode's Pundmann review notes stainless steel tanks and a relief valve rated for mobile use, but also points out there are fewer long-term US owner reviews so far.
Duoetto (Sandy Vans) – A dual-voltage cylindrical tank aimed at the North American market with a straightforward install, though it also asks for more cabinet depth.

A quick note in the interest of transparency: GoCode sells Pundmann units, so keep that in mind as you read their comparisons. At Highland Rigs, we pick hardware based on the build — a client who drives daily and wants free heat from the engine may be best served by Isotemp, while a client with a modest lithium bank and tight cabinetry may be better off with a compact low-draw unit.

Installing a Water Heater in a Sprinter (and Other Vans)

Since Highland Rigs specializes in Mercedes Sprinter conversions, this is where we spend the most time. GoCode's Sprinter install guide lists the most common mounting spots: under the bench by the passenger-side sliding door, near the fuel tank on the driver's side, or inside a galley cabinet if your plumbing already runs that way.

Key install takeaways:

Electric units are the simplest install – mount it, plumb the inlet and outlet, and wire the power (Installing a Water Heater in Your Van).
Coolant tie-ins are a bigger job – tapping the heater core lines can affect cabin heat if done wrong, so use a kit designed for your specific van rather than improvising fittings.
Rectangular units fit Sprinter rear benches well, where cylindrical tanks can be a squeeze.
Insulate exposed lines near the heater if you'll see serious cold.

Building on a different platform? GoCode notes that Ford Transit builds often mount under the bed near the rear wheel wells or beside the galley, and that factory insulation varies by trim. ProMaster builds benefit from a flat floor with no drivetrain tunnel, which makes placement easier.

Whatever the van, the rule we follow at Highland Rigs is the same: lock in the water heater location alongside the fresh water tank and plumbing runs during layout. Moving it after the cabinetry is built is far more painful than planning for it up front.

Water Not Getting Hot? Check These First

Most "dead" water heaters have a simple cause. GoCode's troubleshooting checklist suggests working through these in order:

Power – check the breaker or fuse feeding the heater.
Bypass valve – make sure it's back in the normal position after winterizing.
Power source – on a dual-voltage unit, confirm you're really on the source you think you are (e.g., actually plugged into shore power).
Lukewarm, not cold? – look for a mixing valve or fixture blending in cold water.
Coolant systems – give it real drive time (often 20+ minutes) before expecting hot water.
Element or thermostat – if nothing else fixes it, this is when to call your installer or the manufacturer.

Highland Rigs clients can always reach out to us before pulling panels apart.

Keeping It Running for Years

A van water heater lives a harder life than the one in your house. GoCode's two maintenance articles (Keeping Your Van Water Heater Running for Years and How to Keep Your Van Water Heater Running for Years) boil down to a short routine:

Inspect fittings, clamps, and mounting hardware once or twice a year — road vibration loosens things.
Winterize properly if the van sits in freezing temperatures: drain the tank and set the bypass valve.
Watch for scale in hard-water areas if heating starts taking longer.
Fix small drips right away — water in van cabinetry or wiring causes outsized damage.
Carry a spare fuse and an offline copy of your manual for remote trips.

We walk every Highland Rigs owner through their water system at handoff so these checks feel routine, not mysterious.

The Highland Rigs Bottom Line

Size the water heater to your power system first.
Size the tank to your real shower habits, and remember a low-flow head beats a bigger tank.
Use heat you already have (engine or diesel heater) where it fits, with electric backup.
Plan the location early, alongside your water tank and plumbing.
Keep up with simple maintenance and most problems never happen.

Planning a Sprinter build and want hot water designed in from the start? Get in touch with Highland Rigs and we'll help you choose the setup that fits how you travel.

Sources

Rixen hydronic heating sources:

Written by Highland Rigs Management Team