Testing the Most Powerful 30kW Chinese Diesel Hydronic Heater
If you want to survive arctic boondocking, you need reliable heat — and plenty of it.
So I went all in. I bought the most powerful Chinese diesel hydronic heater I could find on AliExpress… so you don’t have to.
This is the 30-kilowatt diesel liquid heater, a monster that runs on 12-volt DC and standard diesel fuel. It’s the largest heater of its kind available online, and while it’s designed to heat antifreeze or transfer fluid in heavy equipment and trucks, I’ve got much bigger plans for it.
The Vision: Full Hydronic Heating for the Flying Pig
For my bus conversion project — The Flying Pig — I’m designing a complete hydronic heating system that can:
Warm the radiant floors for quiet, even comfort
Provide on-demand hot water for showers, washing, and cooking
Preheat the diesel engine on freezing mornings
Harvest waste heat from the engine while driving
Circulate that heat through air-to-water heat exchangers to warm the interior air
Basically, I’m building a DIY version of an Aqua-Hot or Webasto Thermo Top system — only using non-proprietary, easily sourced components. That way, everything can be replaced or repaired on the road without hunting down specialty parts.
And the hope is that this 30kW diesel heater will become the heartbeat of that entire system.
The Heater: Big, Heavy, and Simple
Like most diesel heaters from AliExpress, this one took about two months to arrive, and the box was destroyed on arrival. That seems to be standard procedure for AliExpress freight.
But once unboxed, the sheer size is impressive. It’s 21 inches long, about 12 inches wide, 9 inches tall, and weighs roughly 20 pounds empty — closer to 30 when filled with fluid.
It’s built from steel, not aluminum, which makes it durable but less efficient at transferring heat. Inside the steel body is a combustion chamber surrounded by a water jacket with internal heat transfer fins. A small pump circulates the fluid through that jacket, pulling heat from the combustion and sending it into your heating loop.
The controls couldn’t be simpler. One switch turns on the pump. The other turns on the heater. It runs up to 85°C, shuts off the burner, and kicks back on once the temperature drops to about 70°C — a 15-degree range that keeps the fluid circulating continuously.
Test #1: The Shakedown Run
Before anything else, I wanted to see how it behaved. So I set up 20 gallons of cold water, about 5 gallons of diesel, and ran it in 20°F weather.
The heater drew 22 amps on startup — more than my 10-amp power supply could handle — so I ended up powering it off one of the bus batteries. Once running, it drew between 9 and 10 amps, with the pump alone pulling around 6 amps.
Surprisingly, it’s quiet. There’s no annoying ticking from the fuel pump like most diesel heaters. Instead, it uses what looks like a solenoid system that opens to let fuel in without the rhythmic “tick-tick-tick” we’ve all come to associate with these units.
The heater ran smoothly, performed as expected, and heated that 20 gallons from roughly 8°C to 85°C in 45 minutes. But it’s not enough to just “work” — I needed to know how efficient it was.
Test #2: Efficiency Test (Full Heat Cycle)
To measure real-world efficiency, I downsized the test to a 5-gallon bucket of water so I could run multiple trials.
I weighed the fuel before and after each run, recorded the water temperatures, and timed only the active burn period.
In this test, the water started at 10°C and ended at 96°C after 12 minutes and 45 seconds, consuming 355 grams of diesel fuel.
When you crunch those numbers, it works out to about 37.9% efficiency, with a real-world output of 7.79 kilowatts.
So while the heater is rated for 30kW, it’s actually delivering a little under 8kW of usable heat — meaning it’s losing roughly two-thirds of its energy to exhaust and body heat.
Test #3: Efficiency at Operating Temperature
For the third test, I wanted to simulate normal operating conditions — maintaining heat once everything was already up to temperature.
This time the water started at 73.4°C and ended at 90.2°C. The test lasted 3 minutes and 30 seconds and used 104 grams of diesel fuel.
The results were even lower: 28.8% efficiency with a real-world output of 6.31kW.
So it’s fast, and it’s powerful — but it’s not efficient.
Where the Energy Goes
The 30kW heater’s exhaust pipe is 2¾ inches in diameter, and it blasts out a ton of wasted heat. You can literally feel the energy loss in the air.
That’s why I’m designing an air-to-water intercooler system that connects directly to the exhaust. The goal is to capture some of that wasted energy and put it back into the heating circuit.
I’m also planning to weld additional heat transfer fins inside the water jacket to improve conduction. If I can push overall efficiency up into the 50% range, I’ll call that a win.
Comparing to the Webasto Standard
This heater is a budget clone of the Webasto Thermo Pro 90, a German-made diesel boiler that runs between 70–90% efficiency thanks to advanced air/fuel control and microprocessor tuning.
But those units cost upwards of $3,000, plus another grand in accessories and controllers. This 30kW clone costs around $300.
So yes, it’s rough around the edges — but it’s also one-tenth the price, and it’s serviceable, simple, and hackable.
Observations and Concerns
One thing that concerned me right away was the rust inside the water jacket. These heaters are designed to use heat transfer fluid or boiler antifreeze, not plain water. Using plain water could cause oxidation and fouling over time.
And while I love the simplicity, the lack of tuning is a limitation. There’s a small air intake dial, but no precise control over the fuel flow or combustion ratio. It’s basically the tractor of diesel water heaters — strong, durable, and simple, but definitely not elegant.
What’s Next
I’ve ordered a 16kW aluminum-body version from the same manufacturer. Once it arrives, I’ll test them side by side to see how much more efficient the aluminum design is compared to this steel-bodied version.
I’m also going to test the intercooler exhaust recovery system and document any improvement in efficiency. My hope is that these modifications can bring the performance closer to the Webasto range — without spending thousands.
If it works, this heater could become the heartbeat of the Flying Pig’s hydronic heat system — providing radiant floor heat, engine preheat, domestic hot water, and warm air circulation all in one setup.
Final Thoughts
For $300, this 30kW diesel heater is an impressive piece of machinery. It’s simple, powerful, and built like a tank — but it’s inefficient.
At roughly 38% efficiency, you’re losing about two-thirds of your diesel energy to waste heat. It works beautifully for short bursts and experimentation but isn’t ideal for long-term use without modification.
That said, it’s a fascinating test platform and a great starting point for anyone building a DIY hydronic heat system. With some tweaking, I think it can evolve into something truly special.
And as always — I do the testing so you don’t have to.
Key Takeaways
Rated for 30kW, but produces around 7–8kW usable output
Efficiency ranges from 28–38% depending on operating conditions
Draws up to 22 amps at startup, about 9–10 amps during operation
Steel body limits heat transfer; aluminum versions should perform better
Best suited for DIY experimentation or short-term heating
Costs around $300 and can be improved with intercoolers and fins
Not efficient yet — but a promising foundation for future upgrades