Put the diesel heater unit inside the van, tucked into a bench seat or under the bed, and drop the exhaust, combustion air intake and fuel line straight down through the floor. The one rule you cannot get wrong: the exhaust has to end past the outer edge of the van, never under the floor, and it has to sit at least 50 cm away from the air intake. Everything else is comfort. That one is safety.
A diesel heater is a small furnace that burns diesel in a sealed chamber and blows warm, dry air into your living space while sending all the fumes outside. That sealed loop is the whole point, and it only works if the outside half is plumbed properly. We learned that the slow way.
Where does the heater unit itself go?
Most first-time builders mount the unit inside, through the floor. The heater sits on top of your floor inside a cabinet, a bench box or the bed base, and only the intake, exhaust and fuel pipes poke through to the underside. This keeps the electronics and the diesel pump out of the road spray and makes servicing far easier.
The other option is mounting the whole unit underneath the van in a protective holder, which frees up interior space. It looks tidy, but everything is now exposed to water, salt and stones, and you are lying on the ground every time something needs a look. For a first build, inside is the more forgiving choice. Wherever it goes, keep the hot body at least two inches clear of anything that can burn: plywood, cushions, a stray curtain.
Where do the exhaust and air intake go?
Both run out through the floor, and they need to be kept apart. The rule of thumb is a minimum of 50 cm between the exhaust tip and the intake, facing opposite directions, so the heater never breathes in its own exhaust. When that happens the flame starves, the unit throws an error, and in the worst case fumes get pulled back inside.
Point the intake slightly downward so rain cannot collect in it. Run the exhaust on a constant downward slope from the heater to its tip, with no dips, so the water that condenses inside the pipe drains out the end instead of pooling and rusting the line.
Why does exhaust placement matter so much?
Because of carbon monoxide, which you cannot see or smell. If the exhaust ends under the van instead of past the edge, CO can collect in the still air beneath the floor and get drawn straight back into the intake, or up through any gap in the floor. The exhaust tip belongs beyond the outer sill of the van, pointing away from doors and windows.
This is the part we got wrong. On our Boxer we first ran the exhaust so it vented just under the floor near the intake side, because it was the shortest route and we wanted it hidden. The heater kept faulting and the CO alarm chirped once on a still night, which is the kind of warning you do not ignore twice. We rerouted the pipe to exit past the chassis edge, added distance to the intake, and the faults stopped. Buy the CO alarm, mount it near your head, and treat it as non-negotiable.
Where does the fuel pump go, and why is it ticking?
The fuel pump is the little unit that clicks. Mount it on an incline with the outlet end raised 15 to 35 degrees above the inlet, pointing up toward the heater, so fuel moves the right way and air does not lodge in the line. Bolt it to a chassis rail rather than a flat panel, because a flat panel acts like a drum and amplifies every tick into the cabin.
If your pump is clicking loudly, it is usually air trapped in the fuel line or the pump vibrating through its mount, not a fault. A rubber grommet between the pump and the bracket, plus getting the angle right, quiets most of it. It never goes fully silent, and that steady tick becomes weirdly comforting on a cold night.
What is the biggest first-build mistake with heaters?
Hiding the exhaust for looks. Almost every heater problem a beginner hits traces back to the outside plumbing: exhaust too close to the intake, exhaust ending under the floor, an intake full of rainwater, or a fuel pump mounted flat and dead quiet at the wrong angle. None of it shows in a photo, all of it decides whether the thing works and whether it is safe.
Get the outside half right first. Unit inside where you can reach it, intake and exhaust 50 cm apart and facing away from each other, exhaust sloping down and out past the edge of the van, fuel pump angled up toward the heater, CO alarm by the bed. Do that and the diesel heater becomes the best 20 euro of comfort per winter in the whole build.
Diesel heater placement: quick answers
Can you mount a diesel heater under the van instead of inside?
Yes, in a protective holder, and it saves interior space. But the unit and fuel pump are then exposed to road spray, salt and stones, and servicing means lying under the van. For a first build we'd mount it inside through the floor, with only the intake, exhaust and fuel line passing underneath.
How far apart should the exhaust and air intake be?
At least 50 cm (about 20 inches), facing opposite directions. Any closer and the heater can draw its own exhaust back into the intake, which starves the flame, triggers faults and risks pulling fumes toward the van. Keep the exhaust tip past the outer edge of the van, never venting under the floor.
Is a diesel heater exhaust dangerous inside a campervan?
The exhaust gas contains carbon monoxide, which is invisible and odourless, so placement is a genuine safety matter, not a detail. Route the exhaust so it ends beyond the van's outer edge on a downward slope, keep it well away from the intake and any window, and fit a carbon monoxide alarm near where you sleep.
Why is my diesel heater fuel pump so loud?
A loud, sharp click usually means trapped air in the fuel line or the pump vibrating through a flat mount. Fix the mounting angle (outlet 15 to 35 degrees above the inlet, pointing toward the heater), bolt it to a chassis rail rather than a flat panel, and add a rubber grommet. A soft, steady tick is normal.
Where is the best place to put a diesel heater in a small van?
Inside a bench seat, under the bed base, or in a low cabinet, anywhere the hot air outlet can reach the living space and the pipes can drop straight through the floor. Keep the body two inches from anything flammable, and choose a spot where the exhaust can run out past the van's edge without a long, dipping pipe run.
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