Free camping ends when the hot water does. You either carry gas bottles you have to refill, or you plug into 240V you do not have.
The Apollo-DH5 runs on the diesel already in your vehicle. One 5KW unit gives you shower water, cabin heat, and warm floors — with the engine off, in the middle of nowhere.
It draws 2.2A at 12V and burns up to 0.55 L/hr. Down to -40°F (-40°C).
Three Jobs, One Tank of Diesel
The Apollo-DH5 is a diesel hot water system built around a diesel water heater bolted to a 15L stainless steel heat-exchanger tank. It leaves the factory as one assembled unit.
You connect three things: water lines, a fuel line, and 12V power.
From that single unit you get:
- Hot water for your shower, sink and outdoor wash — heated indirectly, so it never touches the burner
- Cabin air heat through a 1.7KW coolant-fed fan matrix, for the caravan, campervan or motorhome
- Radiant floor heating, if your build has underfloor pipework
- Windscreen defrost and engine pre-heat on water-cooled vehicles
Most caravan owners end up with two appliances for this — a gas water heater and a separate diesel air heater. This is one appliance, one fuel, one fuel line.
How a Diesel Fired Water Heater Actually Heats Your Shower Water
Your drinking water never enters the heater. It is warmed through a sealed wall of stainless steel.
The loop works in four steps:
- The diesel burner heats a sealed loop of coolant (antifreeze), the same way your engine cooling system works.
- That hot coolant flows into the 15L stainless steel tank on the unit.
- Inside the tank, heat crosses the exchanger wall into your fresh water. The two never mix.
- Heated fresh water flows out to your storage tank, shower and taps.
This matters more than it sounds. A direct-fired water heater puts your drinking water inside a combustion appliance. Here the burner side and the potable side are two separate circuits, and the only thing they share is a stainless wall.
The same hot coolant loop is what feeds your cabin blower and your floor pipes. That is why one unit does three jobs instead of one.
What Size Storage Tank Do You Need
Start at 16-26 gallons (60-100L) of insulated storage for a caravan with a shower and a sink. The heater does not need a coil in your tank, because the heat exchange already happened inside ours.
Work it out from your own use, not from the heater rating:
- A shower runs about 1 gal/min (4 L/min) at normal caravan pressure
- A 5-minute shower is therefore about 5 gal (20L) of mixed water
- Washing up is 0.5-1.5 gal (2-6L)
- Two people showering daily plus dishes lands around 13-16 gal (50-60L) per day
Now the recovery side. A 5KW output raises water temperature at roughly 1.5 L/min from cold. In plain numbers:
- A 60L tank goes from cold to hot in about 40 minutes
- A 100L tank takes about an hour
So the honest way to run this system is: heat the storage tank before you need it, and let good insulation hold it. Two back-to-back 5-minute showers off a pre-heated 60L tank is comfortable. Four people queuing for showers with no pre-heat is not — that is a bigger storage tank problem, not a heater problem.
Your storage tank is not included, and it does not need to be anything special. It needs to be insulated. No internal coil, no heat exchanger, no second appliance.
Your Engine Heats Your Water for Free While You Drive
Waste heat from your engine goes into the same coolant loop and ends up in your storage tank. You arrive at camp with hot water and you burned no extra diesel to get it.
On a touring day this is most of your hot water. The burner only has to make up the difference in the evening.
That is also why this suits the way Australians actually travel — drive four hours, pull up, shower. If you are parked for a week, the burner does the work on its own with the engine off.
Running It on 12V Without Killing Your Battery
The system draws 2.2A at 12V while running, or 1.1A on the 24V version. That is less than a single LED light bar.
Here is what that means for a 100Ah house battery. At 2.2A, a four-hour heating session costs you under 9Ah — under 10% of a 100Ah bank, before you count solar. The circulation pump adds 14W.
Working voltage range is 9V-16V DC on the 12V model, 18V-32V on the 24V. Outside that window the controller shuts itself down rather than dragging your battery flat. The panel tells you which way it went — E-03 for high, E-04 for low.
Fuel use is up to 0.55 L/hr at full output. The controller modulates down as the coolant comes up to temperature, so real-world consumption over an evening sits well below that.
You also get a key-fob remote. Start the heater from bed, or from outside the van, without going to the panel. The remote pairs to the control panel in a few seconds, works to about 100 ft (30m) in the open, and one panel takes two remotes if there are two of you.
Full Specifications — Apollo-DH5
| Heat output | 5KW / 17,000 BTU/h, automatically modulated |
| Fuel | Diesel |
| Fuel consumption | up to 0.55 L/hr (0.15 gal/hr) at full load |
| Rated voltage | 12V (24V version available) |
| Operating voltage range | 9V-16V DC (24V version: 18V-32V DC) |
| Operating current | 2.2A at 12V / 1.1A at 24V |
| Water tank | 15L (4 gal) stainless steel with integrated heat exchanger |
| Water recovery rate | approximately 1.5 L/min from cold |
| Heated coolant temperature | up to 176°F (80°C) |
| Operating ambient | -40°F to 140°F (-40°C to 60°C) |
| Storage temperature | -40°F to 248°F (-40°C to 120°C) |
| Cabin fan matrix | 1.7KW coolant-fed (optional) |
| Minimum coolant volume | 4.0L (1.1 gal) |
| Minimum coolant flow | 250 L/h |
| Circulation pump | 900 L/h at 0.1 bar, 14W |
| Operating pressure | 0.4-2.5 bar (6-36 psi) |
| Heater dimensions | 8.4 x 4.2 x 6.6 in (214 x 106 x 168mm) |
| Certification | CE and RoHS |
The heater core is rated to run in ambient temperatures down to -40°F (-40°C). Cold-start needs coolant below 86°F (30°C), which is a non-issue unless you are restarting straight after a long drive.
What Ships to You, and What You Supply
In the box:
- Apollo-DH5 heater pre-assembled onto the 15L stainless steel heat-exchanger tank
- Circulation pump
- Fuel metering pump and fuel line
- LCD control panel with wiring loom
- Key-fob remote control
- Tempering valve — so your tap temperature is safe without running the tank cool
- Stainless steel exhaust silencer and flexible exhaust pipe
- Combustion-air intake silencer
- Brass fittings, ball valve and hose tails for the water side
- Inline fuel filter
- Mounting hardware, hose clamps and protective sleeving
- Fuel standpipe for drawing from your vehicle tank
- Warning labels
You supply:
- An insulated hot water storage tank, 16-26 gallons (60-100L) for a caravan with a shower. Insulation is all it needs — no internal coil.
- Diesel, drawn from your vehicle tank via the supplied standpipe, or from a separate tank
- A 12V or 24V battery
The exhaust silencer is not optional. Never run the heater without it.
Installation Overview
This is a plumbed and fuelled appliance. Have it fitted by someone who has done fuel-fired heaters before, and check your state's rules before you start.
The numbers your installer will want:
- Coolant hose: 3/4 in (20mm) inside diameter, clamps to 18 lb-in (2.0 N·m)
- Exhaust: 7/8 in (22mm) ID, total length 20-40 in (500-1000mm), max 270° of bends, silencer at least 8 in (200mm) from the heater
- Combustion air intake: 1 in (25mm) ID, max 16 in (400mm) long, silencer pointing 0-90° downward
- Fuel intake line (tank to pump): max 4 ft (1.2m). Delivery line (pump to heater): max 19 ft (5.8m)
- Fuses: main 20A, secondary 5A
Mounting rules that people get wrong:
- Mount the unit low, so the heater and pump self-bleed
- Coolant fittings must never point downward
- Never below the vehicle's wading line, never above the coolant expansion tank, never in the radiant zone of an exhaust
- Exhaust points straight down or up to 20° rearward — never toward the direction of travel, never into the wheel spray
- Never route fuel lines through the living space
Bleed the coolant loop properly and pressure-test every joint before the first real run. Poor bleeding is the number one cause of overheat faults on this type of system — trapped air stops the coolant moving, the heater sees its own heat with nowhere to go, and it shuts down. More installs get bounced back for this than for anything else.
There is more detail in our guide on diesel heater installation precautions.
WaterMark and Australian Compliance — Read This Before You Buy
The Apollo-DH5 is not WaterMark certified. We would rather tell you that here than have you find out at inspection.
What that means in practice:
- WaterMark is the certification scheme under the Plumbing Code of Australia for water and heated water products.
- Victoria still requires WaterMark certified heated water products in newly built caravans and motorhomes, installed by a registered plumber.
- Under current ABCB guidance, most other states do not require WaterMark for hot water systems in caravans and RVs.
- Rules change, and they differ by state. Check with your certifier or state authority before you commit — especially if the van will be registered in Victoria or is being built for sale.
If you are building a new van for registration in Victoria, buy a WaterMark certified unit instead. If you are retrofitting your own van elsewhere in Australia, or fitting out a boat, truck or campervan, this is a decision you get to make.
We are not going to tell you a product is certified when it is not. You can check our actual product certifications — every number on that page is verifiable.
The 60°C Question Nobody Selling These Talks About
Legionella bacteria die above 140°F (60°C) and multiply between 68-113°F (20-45°C). Any stored hot water system has to deal with this, gas or diesel.
The Australian standard for heated water services, AS/NZS 3500.4, is written around storing water above 140°F (60°C) for exactly this reason. It binds buildings; a private caravan is regulated as a vehicle, so treat it as best practice rather than paperwork.
This is why a tempering valve comes in the box. It lets you do the right thing on both counts at once:
- Store the water hot — run your tank up to 140°F (60°C) rather than sitting at a lukewarm 105°F (40°C)
- Deliver it safe — the valve mixes it back down to about 122°F (50°C) at the tap, so nobody gets scalded
- If you have been parked for weeks without using the shower, do a full hot cycle before you use it again
The coolant loop runs up to 176°F (80°C), so reaching a proper 140°F (60°C) storage temperature is well within the system's range. The valve needs about 18°F (10°C) of headroom to work, and hot storage gives it exactly that.
What This Is Not
Buying the wrong category is the most expensive mistake in this market. Four things this is not:
Not a tankless or instant water heater. It has a 15L exchanger tank and it heats a storage tank at about 1.5 L/min. If you want endless hot water on demand with no storage, you want an LPG instant unit — different product, different trade-off. Ours holds heat and works off the fuel already in your vehicle.
Not a portable camping shower. Those are the small gas units that clip on the back door and run off a bottle. This is a permanently installed vehicle system that also heats your cabin and your floor.
Not a 240V or shore-power appliance. It runs on 12V battery power and diesel. That is the whole point — it works where there is no power.
Not an industrial diesel hot water boiler. If you are sourcing a boiler for a building, a wash bay or a process line, this is not that product and the ratings are nowhere near what you need.
Petrol Vehicle? There Is a Gasoline Version
If your vehicle runs on petrol, you do not want a diesel heater and a separate diesel jerry can.
The Apollo-GH5 gasoline hot water system is the same architecture on the same platform — same 5KW output, same indirect heat exchange, same three functions. It draws from your petrol tank instead. It is 12V only.
You cannot run a diesel unit on petrol. The burner, the metering pump and the ignition are built around the fuel. Pick the one that matches your tank.
Why This Costs More Than a $200 Unit
Ask any caravan repairer in Australia what comes across their bench. It is the cheap unit that stopped working a month after purchase, with no warranty and no parts.
The parts problem is the real one. Components from the various no-name factories are often not interchangeable, so when a pump or a glow pin fails there is nothing to fit. A unit you cannot repair is a unit you replace.
What you are paying for here:
- A stainless steel heat-exchanger tank, not a painted mild steel one that weeps at the seams after two seasons
- A complete, matched kit — pump, metering pump, control panel, remote, tempering valve, both silencers, hoses, clamps and standpipe in one box
- Parts that stay available, from a manufacturer that has been building vehicle heaters since 1996
- A real person to email when something does not make sense, in English, with the wiring diagram in front of them
We are not the cheapest diesel hot water system you will find and we are not trying to be. We sell to people who do not want to do this job twice.
Frequently Asked Questions
Can one unit heat my shower water and my caravan at the same time?
Yes, and that is the main reason people buy this instead of two appliances. The burner heats one coolant loop, and that loop feeds both the water tank and the cabin blower.
Output is shared, not doubled. On a bitter night with the cabin heater running hard, water recovery slows down. In practice you heat the water tank before or after the evening, not during the coldest hour.
Order it with the cabin air heater if you want both from day one.
My water is hot in the tank but the tap runs cold. Is the heater faulty?
Usually not. The most common cause of "no hot water" in a caravan is a failed or blocked tempering valve, not the heater.
Check it before you touch the heater: if the storage tank itself is genuinely hot and the taps are not, the valve or its inlet filter screen is the suspect. The screens block up with sediment from campground water, and a rinse often fixes it.
Do not just remove the valve and fit a straight connector. People do this and end up with no hot water at all, because the valve is what mixes the hot storage down to a safe tap temperature.
The circulation pump gurgles and the heater shuts down on an overheat fault. What is wrong?
That is trapped air in the coolant loop, and it is the single most common installation fault on this type of system.
Air stops the coolant circulating. The burner keeps producing heat with nowhere to send it, the overheat sensor trips, and you get E-11. Three of those in a row locks the heater out with E-12.
The fix is to bleed the loop properly. Mount the unit low, route hoses uphill from the heater, and fill through the radiator cap with the fittings never pointing downward. To clear an E-12 lockout, switch off, pull the 20A fuse for three seconds and refit it — then fix the air before you restart.
How long does it take to heat my water, and how many showers do I get?
From cold, expect roughly 40 minutes for a 16 gal (60L) tank and about an hour for a 26 gal (100L) tank. Recovery runs at approximately 1.5 L/min.
A 5-minute shower uses about 5 gal (20L) of mixed water. Off a pre-heated 60L tank, two people can shower back to back comfortably.
Four people expecting hot showers in a row need a bigger storage tank, not a bigger heater. Pre-heat it and insulate it properly and this is a non-issue.
Do I need a WaterMark certified system in Australia?
It depends on your state and on whether the van is new. This unit is not WaterMark certified.
Victoria still requires WaterMark certified heated water products in newly built caravans and motorhomes, fitted by a registered plumber. Under current ABCB guidance, most other states do not require it for hot water systems in caravans and RVs.
If you are building a new van for Victorian registration, buy a certified unit. If you are retrofitting your own van elsewhere, check with your state authority first — the rules have moved more than once.
Does the water go cold halfway through a shower?
Not if you pre-heat, but there is a real limit and we would rather you know it.
Heat transfer into your storage tank keeps running while you shower, at about 1.5 L/min. A long shower can draw hot water faster than that, so temperature drifts down towards the end.
Two things fix it: start with the storage tank fully up to temperature, and insulate the tank and the hot lines. A well-insulated 60L tank holds usable heat overnight.
I already have a gas hot water system. Is diesel actually worth swapping to?
The argument is fuel logistics, not efficiency. If your vehicle already runs on diesel, this uses the tank you refill anyway, and you stop carrying and refilling gas bottles.
That matters most if you free camp for long stretches. It matters less if you are on powered sites where refilling gas is easy.
The other half of the argument is that it replaces two appliances with one. If you were going to fit a diesel air heater as well, a combined system is one fuel line, one exhaust and one hole in your floor instead of two.
What is wrong with the cheap diesel water heaters on eBay?
Two things: what is inside them, and what happens after they fail.
A $200 unit and a $1,500 unit can look nearly identical in photos. The differences are in the heat exchanger material, the burner assembly and the build tolerances — none of which show up until the second winter.
The bigger problem is parts. Components from the various no-name factories are frequently not interchangeable, so when the metering pump or glow pin goes there is nothing to fit and no warranty behind it. Repairers see this constantly. A unit you cannot get parts for is disposable, whatever it cost.
Ready to Order
The Apollo-DH5 ships as one assembled unit with everything in the list above. Choose whether you want the cabin air heater included — pick Heater Only if your build already has cabin heat and you only need hot water and floor heating.
Need the 24V version? Email us before you order and we will sort it out.
Not sure it fits your build? Email us at info@vvkb.com with your vehicle, your tank size and what you want heated, and we will tell you straight whether this is the right unit.
See the rest of the range: diesel hydronic coolant heaters
