Surprising 67% Efficiency in the HLN 10kW Diesel Hydronic Heater
Can a Steel Heat Exchanger Really Beat Aluminum?
You know, when most of us think steel heat exchanger, we think cheap, heavy, inefficient. I thought the same thing—until this test.
Today, I’m putting HLN’s 10kW diesel hydronic heater to the ultimate test to find out if a steel-bodied unit can outperform even the best aluminum models I’ve ever tested. Spoiler: it did. And not by a little—it hit 67% efficiency, the highest I’ve ever seen from any unmodified diesel hydronic heater.
🔧 The Setup
For this test, I wanted to keep everything standardized—same protocol I’ve used on all my previous reviews.
Fuel: Standard road diesel
Power: 12V DC supply
Test Load: 5 gallons of water
Instrumentation: digital thermometer, precision fuel scale, and stopwatch
The heater was bench-mounted with its intake muffler and exhaust properly routed. Below, a five-gallon bucket of water acted as the heat sink. I measured both starting and ending temperatures, timed the full burn cycle, and weighed the fuel used before and after.
Once it fired up, I immediately noticed how quiet it was. Even though it’s a steel-bodied heater, it’s got this refined hum—more like a small furnace than the usual chattery diesel unit. The pump is the familiar “clicker” style, but quieter than most, and the brushless fan motor is whisper-smooth.
⚙️ The Control System & Wi-Fi Integration
The HLN’s controller surprised me. It’s not some cheap knock-off LCD—this one has a full-featured interface with a simple power button, day/date display, timer scheduling, and even Wi-Fi connectivity through the My Smart Life app.
From your phone, you can:
Turn the heater on/off remotely
Set timers for specific times or days
Monitor voltage and adjust low-voltage cutoff (factory default: 8.0V)
For anyone running a 12V off-grid setup with limited battery capacity, that’s a huge plus—it prevents your system from deep-cycling your batteries.
🔥 The Test Results
After firing up and reaching stable operation, here’s what happened:
Starting temperature: 16.5°C
Final temperature: 65°C
Elapsed time: 8 minutes, 37 seconds
Fuel used: 127.8 grams
When you crunch the numbers, that translates to:
Thermal efficiency: 67.1%
Power output: 7.43 kW (≈25,000 BTU/hr)
That’s remarkable. For context, my big 30kW steel-bodied heater managed only 32% efficiency, and my top-performing aluminum model landed around 64%. So this compact 10kW unit just beat both.
And this wasn’t some modified setup with an exhaust gas recirculator or intercooler. This was straight out of the box.
🧠 Why It Works: Design Trumps Material
So how does a steel unit out-perform aluminum? Here’s what I found when I tore it down:
Longer Combustion Chamber: The flame has more residence time inside the exchanger, meaning more heat is absorbed before the exhaust exits.
Tight Proximity to Fins: The combustion chamber sits snug against the fin array—no wasted air space, no cold spots.
Triple Fin Density: Compared to the 30kW heater, this has roughly three times as many fins—and they’re shark-tooth shaped for turbulence and greater surface area.
Massive Thermal Mass: The heat exchanger block is thick, heavy, and perfectly machined. That extra mass stores and releases heat steadily, improving consistency.
Smart Software: The onboard controller adjusts air–fuel ratios automatically for efficiency and even compensates for elevation changes.
It’s clear that HLN focused on design precision, not just wattage ratings. The result is a heater that sips fuel, transfers heat efficiently, and maintains temperature with minimal cycling.
🧩 Build Quality and Components
Like all HLN products, this thing oozes quality from the inside out.
Brushless fan and pump motors for durability and silence
Magnetic steel housing, thick powder coat finish
High-quality connectors with O-rings and weather seals
Neat wiring harness with labeled plugs and strain reliefs
Proper English documentation and actual support contacts
Even the accessories impressed me: a corrugated intake silencer, heavy-duty wiring harness with detachable power plug, rash guards for fuel lines, clamps, heat shrink, and a quiet pump. Everything feels like a kit meant for professional installation.
HLN clearly isn’t cutting corners here. Every fastener was torque-marked by QA staff, and even the inside of the housing looks aerospace-clean.
📊 Efficiency in Context
To put things in perspective:
30kW Steel Heater (budget clone): ~32% efficient, ~7.4 kW output
9kW Aluminum Webasto clone: ~64% efficient, ~6.7 kW output
HLN 10kW Steel Heater: 67% efficient, 7.43 kW output
So despite being steel, the 10kW HLN runs more efficiently than any heater I’ve tested—and at the time of this writing (May 2025), it’s priced at $699 USD, shipped. That’s cheaper than most high-end clones and a fraction of what name-brand hydronic systems like Webasto or Aqua-Hot charge.
🧩 Inside the Heat Exchanger
Here’s what makes this heat exchanger unique:
Extra-long combustion tunnel
Tight fin spacing and complex geometry
Increased fin depth and serrated edges for better air mixing
Fins mounted directly against the combustion wall for faster transfer
It’s like comparing a small car radiator to a big turbo intercooler—the mass and density make all the difference.
🛠️ Real-World Usability
This heater feels purpose-built for serious off-grid and mobile applications:
Ideal for: buses, vans, RVs, cabins, food trucks
Supports radiant floor heat, fan coils, or domestic water via a plate exchanger
Can preheat diesel engines or scavenge waste heat during driving
Integrates with thermostats or smart controls
If you’re building a hydronic system, pair this heater with:
A 17-gallon aluminum heat battery or tank
A 12V DC circulation pump (3 GPM)
A plate heat exchanger for potable water
An expansion tank (~10% of your total system volume)
💬 Transparency & Support
For full disclosure, HLN sent me this heater to test and review. They didn’t pay me, and they have no control over what I say. These are my genuine results and impressions.
If you have technical questions or want to order one:
Email Kevin: kevin.hln.int@gmail.com
Visit: HLN Official Website
Product Page: Aquano 10k Coolant Heater
And if you decide to buy one, use code %JasonHurst for 20% off any HLN product. That affiliate link helps me keep testing these systems and sharing the data honestly.
🧠 Final Thoughts
After testing more heaters than I can count, this one surprised me. The HLN Aquano 10kW has officially changed how I look at steel-bodied heat exchangers.
It’s heavy, overbuilt, quiet, and shockingly efficient.
If you’re designing a hydronic system for your bus, van, or cabin—and you want reliability without paying brand-name prices—this one’s a winner.
I’ll keep it simple: HLN just raised the bar.