Fitting a diesel heater is one of the more involved DIY jobs on a caravan, but it is well within reach of a confident owner with a free day and the right approach. This guide walks through the whole install, from choosing a mounting spot to the first priming run, and flags exactly where the work has to be spot on and where you should hand it to an installer.
Before you pick up a drill, understand what you are installing. A diesel heater is a sealed unit that pulls in a little diesel, burns it in a combustion chamber, and blows warm air into the van while venting all the exhaust and moisture outside. That means four separate services all have to be run correctly: fuel, exhaust, combustion air and 12V power, plus the warm-air ducting on top. None of them are difficult on their own. The skill is in planning them together so the runs are short, tidy and safe.
Set aside a full day, work in a clear space with the van level, and read the instructions that come with your specific kit. Brands differ in the fine detail, and the numbers below are typical guidance, not a substitute for the manufacturer’s figures.
Plan the Install and Choose a Location
Most of a good install is decided before you drill a single hole. The heater lives inside the van but breathes through the floor, so the mounting spot has to work for both the warm air going into the cabin and the fuel, exhaust and intake pipes going down and out underneath.
The two classic locations are inside a front boot or storage locker, or under a fixed seat or dinette. Both keep the unit out of the way and give you floor access underneath. Look for a spot that has clear floor below it (no chassis rail, tank or wiring loom directly under where the pipes will pass), that sits reasonably central so the warm-air duct reaches the living area, and that lets you run the exhaust out to a safe, open point clear of windows and vents.
Sketch the whole layout first. Mark where the unit sits, where the fuel tank goes, where the exhaust will exit, and where the warm air comes out. Keep the fuel line as short and as high as practical, keep the exhaust run short, and avoid tight kinks in any pipe. A little planning here saves you drilling a hole in the wrong place with a fuel line already committed.
Mock the whole install up loosely before you commit. Sit the unit in place, lay the pipes out on the floor, and hold the tank where it will live. You will spot the clashes on the bench, not halfway through with holes already cut.
Mount the Heater Unit
With the location settled, mount the unit. Most heaters bolt to a mounting plate or gasket that seats over a single large hole in the floor, through which the fuel, exhaust and combustion air connections drop down to the outside world. Use the template supplied with your kit to mark the hole and the bolt positions.
Before you cut, go underneath and double check there is nothing in the way: no chassis member, no water tank, no wiring or gas line, and enough clearance for the pipes to hang and route away cleanly. When you are certain, cut the main aperture and the bolt holes, deburr the edges, and seal the cut edges if the floor is timber so it cannot soak up moisture.
Bed the mounting gasket down on a suitable sealant, sit the unit in place, and bolt it down firmly. The gasket seal matters: it is what stops road spray, dust and, critically, any exhaust from finding its way up into the van. Make sure the unit sits square and the outlet spigot points the way you planned for the ducting.
Fit the Fuel Tank, Line and Pump
The fuel side is where care pays off. You have two options: plumb into your existing supply, or fit a small dedicated tank. For a caravan, a dedicated 5 to 10L tank mounted in the tunnel boot or under the van is the tidy choice, because it keeps the van self-contained and you are not tapping the tow vehicle. Mount the tank securely so it cannot shift, with the pickup at the bottom.
The metering pump is the heart of the fuel system. It should be mounted at the angle the manufacturer specifies, usually somewhere between 15 and 35 degrees nose-up, with the outlet higher than the inlet so it self-bleeds and does not sit full of air. Mount it on the rubber grommets provided and away from the bed head, because the pump ticks steadily while running and you will hear every beat if it is bolted hard to the floor under your pillow.
Run the plastic fuel line from the tank pickup, to the pump, and up to the unit, keeping it clear of the exhaust and away from anything hot or sharp. Support it with clips every so often so it cannot rub through or sag into a low loop that traps air. Keep the run rising gently towards the pump where you can, and trim it to length rather than coiling metres of excess line.
Get the fuel connections right. Every joint must be firm and leak-free, and the line must be routed well clear of the hot exhaust. A diesel leak near a running heater is a serious fire risk. If you are at all unsure about the fuel plumbing, this is the part to hand to a professional installer.
Route the Exhaust and Combustion Air Intake
The exhaust and the combustion air intake both connect to the underside of the unit and both vent outside, but they do very different jobs. The intake draws fresh outside air into the sealed burner. The exhaust carries the burnt gases, including carbon monoxide, away from the van entirely. Getting the exhaust placement right is the single most important safety decision in the whole install.
Run the exhaust pipe from the unit downward and outward, sloping it so any condensate drains out rather than pooling back towards the burner. Keep it as short and as straight as the layout allows, support it with the clamps and brackets provided so it cannot vibrate loose, and terminate it pointing down or out at a spot that is well clear of the van’s exterior. The intake runs the same way but stays separate, and its opening must sit away from the exhaust outlet so the burner never draws its own fumes back in.
The exhaust gets very hot. Keep the pipe away from anything that can melt, char or catch, use the supplied heat shielding through the floor, and route it so nobody can brush against it when it is running.
Terminate the exhaust well clear of every window, roof hatch, door, hopper vent and the underfloor storage. Exhaust gas contains carbon monoxide, which is invisible, odourless and deadly. A poorly placed or leaking exhaust can draw fumes back into the van while you sleep. Keep the outlet at the outer edge of the van, point it away from any opening, and fit a carbon monoxide alarm in the living space regardless of how tidy the install looks.
Wire the 12V, Fusing and Controller
A diesel heater runs on 12V and draws surprisingly little once it is going, well under 1.5 amps for the fan and pump. The catch is the glow plug on startup, which spikes to 8 to 12 amps for a minute or two, so the wiring has to be sized for that peak, not the running load.
Run the supplied loom from the unit back to a suitable 12V source. The cleanest option is a dedicated feed straight from the battery or a fused distribution point, using cable of the gauge the manufacturer specifies and no thinner. Fit the inline fuse the kit provides, close to the power source, so the whole run is protected. Undersized cable or a long thin run causes voltage drop, and a diesel heater that is not getting clean 12V will throw low-voltage faults and struggle to start.
Mount the controller somewhere handy in the living area, at the dinette or by the bed, and run its lead back to the unit. A digital controller with a thermostat and timer is worth the effort here: set it to fire up before you wake and the van is warm before your feet hit the floor. Double check polarity before you connect anything, because reversed 12V can damage the control board.
Wire the heater so it draws from the house battery, not a circuit that switches off with the van isolator. You want to be able to run it overnight without leaving other systems live, and without it dropping out when you flick the master switch.
Run the Warm-Air Ducting and Outlet
The warm-air side is the easy part, and the payoff for all the work underneath. The unit blows heated air out of its outlet spigot, and your job is to carry that air to where you actually sit and sleep. Connect the flexible ducting to the outlet, and run it to a vent or louvre positioned to throw warm air into the main living space.
Keep the duct run as short and as straight as you can. Every bend and every extra metre robs a little airflow and warmth by the time it reaches the outlet, so route it directly rather than looping it around the locker. Make sure the intake side of the unit, the vent that lets it pull cabin air back in to reheat, stays clear and is not smothered by stored gear. The heater recirculates air from inside the van, so it needs to breathe on the return side as well as blow out the front.
Finish the outlet with the louvre or directional vent supplied so you can aim the warm air, and site it low if you can, since warm air rises and a low outlet warms the floor space where it counts.
First Run and Priming
With everything connected, it is time to bring it to life. The fuel line runs dry from the factory, so the first start involves priming, pushing diesel all the way from the tank, through the pump, to the burner. Many controllers have a dedicated prime function; if not, the first couple of start cycles will pull the fuel through, and it is normal for the unit to try, stall, and try again while the line fills.
Once it lights, expect a bit of smoke and a whiff of diesel for the first few minutes as the assembly oils and any manufacturing residue burn off. This clears quickly. Let the heater run up to full temperature and check the whole install while it is hot: no fuel weeping at any joint, the exhaust venting cleanly outside with nothing hot touching a pipe, warm air coming through the outlet, and the controller reading and responding correctly.
Then do the most important check of all. With the heater running, go inside, close the van up as you would overnight, and confirm your carbon monoxide alarm stays silent. If you smell exhaust inside or the alarm so much as chirps, shut the heater down and find the leak before you use it again.
Fuel and 12V are the two areas where a mistake bites hardest. A weeping fuel joint near a hot exhaust, or undersized wiring that overheats, are not faults you want to discover on a cold night in a remote camp. If the fuel plumbing or the electrical side is beyond your confidence, pay an installer to do those parts. There is no shame in it, and it is money well spent.
- Plan the whole layout before you drill, so the fuel, exhaust, intake and warm-air runs all stay short and tidy.
- Mount the unit on a well-sealed floor gasket, and route the exhaust well clear of every window, vent and hatch.
- Take extra care with the fuel plumbing and the 12V wiring and fusing; these are the parts to hand to an installer if you are unsure.
- Prime the line on first start, expect a little smoke, then run it hot and confirm your carbon monoxide alarm stays silent with the van closed up.
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