How to use a Diesel Hydronic Heater in Your Bus, Van, RV, Cabin, or Food Truck
If you’ve watched my other videos on diesel hydronic heaters and thought:
“Okay, cool science, Jason… but what would I actually do with one of these?”
That’s exactly what we’re getting into today.
Hydronic diesel heaters look intimidating at first, especially compared to a simple air heater that just blows warm air into your rig. But if you’re willing to do a bit more plumbing and wiring, a small liquid heater can turn into the heart of a complete off-grid heating system:
Warm floors
Warm air
Hot showers
Engine preheat
Freeze protection
Heat scavenging while you drive
All from one burner.
Quick Note on the Heater I’m Using
The specific diesel heater shown in this video is no longer in production.
These days, if you’re trying to build a real hydronic system, I recommend looking at the HLN Aquano 10k Coolant Heater . It’s more efficient, better built, and purpose-designed for this kind of setup.
You can grab one here:
HLN Aquano 10k Coolant Heater (use code %JasonHurst for 20% off at checkout and support )
Works great as the core heat source for everything I’m about to describe.
The concepts in this post apply whether you’re using that heater or a similar 7–10 kW diesel coolant heater.
First Reality Check: Power vs Expectations
Most “instant” home water heaters use massive burners with hundreds of thousands of BTUs. Your typical diesel hydronic heater in this category is around 7–10 kW, roughly 24,000–34,000 BTU.
Translation:
It’s not a true one-pass instant water heater for ice-cold water to endless steaming showers.
So the way to win is:
Store heat in a tank (a heat battery).
Move that stored heat where you need it using pumps and heat exchangers.
Once you start thinking of it as a heat battery + distribution system, everything clicks.
Core Concept: The Heat Battery (Buffer Tank)
Instead of running your hydronic heater directly to a single load, you run it into a tank.
I’m using an aluminum tank (around 17 gallons) as my heat battery:
Heater circulates boiler fluid (glycol mix) through the tank.
The tank is insulated to reduce heat loss.
The heater brings that fluid up to around 80–85°C.
That stored heat becomes your “fuel” for floors, water, engine, and air.
You don’t have to weld; lots of people use:
Make it stand out
The key is:
Use a tank rated for hot fluid.
Give the system an expansion path (not a sealed, rigid loop).
Treat it like a battery: charge it with diesel, spend it wherever you need heat.
Pump Strategy: How You Move the Heat
Once your tank is hot, you use circulation pumps to send that heat to specific jobs.
Important points:
Use pumps rated for hot fluids (up to at least 85°C / 185°F).
For mobile rigs, 12V DC circulation pumps are great.
For cabins/shops, AC hydronic pumps work well.
Wire all pumps to a labeled switch panel or controllers so you can choose:
“Floor Heat”
“Engine Preheat”
“Hot Water”
“Fan Coil / Air Heat”
“Gray Tank Protection”
Each pump = one “branch” of your system. That’s what makes this so flexible (and so fun, if you like tinkering).
Use Case #1: Radiant Floor Heat (Bus, Van, RV, Cabin)
This is the simplest and most satisfying use.
Flow looks like this:
Diesel heater heats the fluid in your buffer tank.
A 12V circulation pump sends that hot fluid through Oxygen Barrier PEX in your floor.
A manifold (3–4 zones is common) lets you balance different floor loops.
A thermostat controls the pump on/off, not the heater directly.
4 Loop PEX Manifold
Tips:
Use oxygen-barrier PEX for hydronic loops.
Insulate under the PEX so you’re heating your living space, not the road.
For a 7–10 kW heater, think:
Van, small RV, skoolie, tiny home, or one motorcoach-sized space.
Don’t oversize the square footage beyond what the heater can keep warm on your coldest realistic nights.
Result: silent, even, “toasty floor” comfort that feels way better than blast-you-in-the-face hot air.
Use Case #2: Engine Preheat (Cold-Weather Diesel Starts)
If you’ve ever tried to start a cold-soaked diesel, you know.
Using a plate heat exchanger, you can:
4” x 12” 20 Plate Heat Exchanger
Keep your hydronic loop (glycol in your tank) separate from the engine coolant.
Use one pump on the hydronic side, one on the engine side.
Transfer heat from your tank into your engine block before you ever turn the key.
Typical scenario:
Turn on the engine preheat loop 45–60 minutes before start.
Hot hydronic fluid runs through one side of the plate exchanger.
Engine coolant runs through the other.
Heat moves into the block, heads, and coolant.
Result: easier starts, less wear, happier batteries, happier you.
Bonus: You can flip it the other way while driving.
Engine up to temperature?
Run the plate exchanger the other way.
Steal “waste heat” from the engine and store it in your heat battery.
Arrive at camp with pre-heated water and floors, sometimes without ever firing the diesel heater.
This is where hydronic systems get really cool.
Use Case #3: Potable Hot Water (Vanlife, Food Trucks, Off-Grid Homes)
Here’s where people get tripped up:
A 7–10 kW heater cannot take ice-cold water in one side and spit out endless hot water on the other like a big home tankless unit.
You have two good options:
Option A: Plate Heat Exchanger at the Point of Use
Use your hot hydronic loop on one side.
Cold potable water on the other.
When a pump + faucet turn on, you get near-instant hot water.
Perfect for:
Hand washing
Dishes
Short, conservative showers
But:
You’re limited by how much heat is in your buffer tank.
Long or reckless use can drain your stored heat.
Option B: Marine Calorifier (My Choice)
A calorifier (marine-style water heater) has:
Marine Calorifier
Standard water heater ports (in/out, T&P valve, drain)
An electric element
An internal heat-exchanger coil
You can
Heat your 11-ish gallons via solar/shore power when available.
Or pump your diesel-heated hydronic fluid through the internal coil to heat it with diesel.
This gives you:
Electric + diesel flexibility
A well-insulated tank that holds temp for many hours
Domestic hot water that isn’t 100% tied to “heater on right now”
For a food truck, skoolie, cabin, or bus: this is a killer combo.
Use Case #4: Freeze Protection (Gray Tank, Critical Plumbing)
One of the less glamorous but huge quality-of-life perks:
Run a loop of oxygen-barrier PEX inside your gray tank.
Use proper bulkhead / gland fittings so it’s sealed.
When temps plunge and your gray tank gets slushy:
Flip a switch.
Pump hot hydronic fluid through that coil.
Thaw the tank so you can dump without turning it into a popsicle block.
Same concept works for:
Vulnerable plumbing bays
Compartments with valves and filters
Exterior tanks
Not a “run it 24/7” feature — more of an “oh crap, it’s 5°F and my tank is frozen” tool.
Use Case #5: Warm Air with Fan Coils (Like Your Vehicle Heater Core)
If you want classic warm air (like a furnace), you don’t need a separate diesel air heater.
You can:
Run hot hydronic fluid through small air-to-water heat exchangers (heater cores).
Add 12V fans behind them.
Put them:
Under seats
In bedrooms
In the front lounge
Control them via thermostats and switches.
Make it stand out
12V Hydronic Heater Assembly Mountable Switch 4 Front Vents 3-Speed Fan 80 CFM Airflow 8500 BTU of Heat
This gives you zoned, quiet, dry heat anywhere you want it — all powered by the same diesel heater + tank.
The Downsides (Let’s Be Honest)
Hydronic systems are awesome… but they are not plug-and-play.
Be ready for:
Multiple pumps
Multiple switches or controllers
Lots of hoses, fittings, clamps
Expansion, air bleed points, service valves
Real layout planning
If you cheap out on pumps or fittings, or make everything impossible to reach, future-you will hate current-you.
My rules:
Every pump gets service valves and quick disconnects.
Every component is mounted so I can remove it without draining the whole system.
Use quality line, clamps, and hardware.
Think like a mechanic who has to fix this on a cold night.
Do that, and the complexity becomes manageable… and the payoff is huge.
Why I Built My Own System Instead of Buying Aqua-Hot
Commercial systems like Aqua-Hot and similar are fantastic pieces of tech.
They’re also:
Expensive
Proprietary
Sometimes painful to service on the road
My approach:
Use widely available components:
Diesel hydronic heater (like the HLN Aquano 10k)
Plate heat exchangers
Marine calorifier or buffer tank
Off-the-shelf circulation pumps
Readily available fittings and PEX
Design the system myself so:
I understand every connection
I can diagnose problems quickly
I can fix it with basic tools and common parts
Same end goal:
Warm floors, warm air, hot water, engine preheat — just without the dealer network and proprietary control boards.
Is a Hydronic Diesel System Right for You?
Choose this route if:
You like to build and tinker.
You want one heat source that can do many jobs.
You care about comfort (radiant floors, silent heat, long hot showers).
You’re okay with a more involved install in exchange for long-term flexibility.
Stick to a simple air heater if:
You just want “less cold air now.”
You don’t want to mess with plumbing.
You’re in a small rig with modest needs.
But if your brain lit up reading through use cases — floors, engine preheat, heat scavenging, gray tank thawing, on-demand hot water — then a hydronic system is absolutely worth exploring.
Gear Mentioned / Starting Points
HLN Aquano 10k Coolant Heater – use code %JasonHurst for 20% off
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