Diesel heater install in a camper van: floor mount vs seat base, step by step

Heating November 4, 2026

Where to mount a diesel heater in a camper van (under the seat, on the floor or under the van), how to install it step by step to Webasto's rules, and how to stay safe from carbon monoxide.

A diesel heater install in a camper van comes down to one decision and one rule. The decision is where the heater body sits: under the van, on the van floor inside a cabinet or bench, or inside the front seat base. The rule doesn't change with location: combustion air must come from outside the van and the exhaust must leave outside it, through sealed, gasketed holes in the floor, with the exhaust pointing away from doors, windows and vents. Webasto's Air Top 2000 STC installation manual is explicit that combustion air "must not be extracted from the passenger cabin" and that the exhaust outlet must be placed so fumes can't get back in through vents or open windows. Get those right, fit a carbon monoxide (CO) alarm, and the location choice comes down to space, access and noise.

This guide compares floor mounting with seat-base mounting, walks through the install step by step, and covers fuel, exhaust and CO safety. The figures come from Webasto's US installation manual for the Air Top 2000 STC. Budget heaters from other brands follow the same principles, but always check limits in your own unit's manual. Once the heater is running, see how to stop condensation in a camper van in winter: a diesel heater is one of the best tools for that job.

Floor mount vs seat base vs under the van

All three locations work if the heater is sealed to the floor and the intake and exhaust run underneath the van. The differences are practical.

Location	Pros	Cons	Best for
Interior floor mount (cabinet, bench or under the bed)	Easy to reach for service; short, simple ducting; you choose where to drill	Uses cabinet space; fan and pump noise inside the living area; needs a clear floor area and a heat-safe enclosure	Full conversions with a galley or bench near the middle of the van
Front seat base (usually passenger side)	Uses dead space; warm air comes out near the cab; nothing taken from the build	Tight fit; can clash with swivel seats, batteries or factory wiring; seat must come off for service	Smaller builds, vans with a passenger seat base that isn't already full
Exterior under-floor mount	No interior space used; quietest inside; combustion parts stay outside the living area	Exposed to road spray, salt and grit; needs a sturdy bracket; awkward to service	Vans with no free interior space, truck campers, and owners who want combustion outside

Webasto's manual allows the heater to be fitted inside or outside the vehicle. If it's outside, it must be protected from splash and spray, and water must not be able to get in when the van fords water it's designed to handle. Inside, the openings for the combustion air inlet, exhaust outlet and fuel line must be sealed with the supplied gasket, and Webasto says that gasket must be replaced each time the heater is removed and refitted.

When the seat base makes sense

The seat base is popular because it costs you no build space and puts warm air low down near the front, where it can help keep the cab glass clear. The catch is what's already there. Owners on VW T6 forums report that the passenger side is often crowded with wiring looms and fuses, and a swivel seat plate can leave too little height for the heater and its duct. Check clearance with the seat fully swivelled before you drill anything. On a Ford Transit, Ram ProMaster or Mercedes Sprinter, check the seat base for factory wiring, airbag or seat-belt sensor harnesses and any underbody crossmembers or the fuel tank, then pick a drilling spot from underneath first.

When a floor mount is better

A floor mount inside a cabinet is usually the easiest DIY layout. It's simpler to reach the heater for service, the ducting can run straight to where you want heat, and you can choose a drilling point clear of the fuel tank, exhaust and frame rails. Plan for the fan and fuel-pump ticking to be audible, and keep the enclosure vented and clear of anything flammable. Webasto's rules say nearby body parts and components must be protected from excessive heat, and the heater must not pose a fire hazard even if it overheats.

Parts and tools checklist

Heater kit: heater, mounting gasket, fuel pump (metering pump), fuel filter, fuel line, combustion air intake hose, metal exhaust pipe and muffler, ducting, controller and wiring harness
A fuel pickup: a standpipe in a separate tank, or a vehicle-specific connector for your van's auxiliary fuel port
Hole saw and drill, deburring tool, rust-proofing paint or primer for every cut edge, sealant
Correctly sized fuse and cable for the 12 V feed, run straight to your house battery or distribution
Exhaust clamps and P-clips, heat-resistant sleeve where the exhaust passes near anything that can melt
A CO alarm listed for recreational vehicle use (see the safety section below)

Diesel heater install in a camper van, step by step

Pick the spot from underneath first. Crawl under the van and find a flat area of floor clear of the fuel tank, exhaust, frame rails, brake lines and wiring. Webasto requires at least 100 mm (about 4 in) between the fuel tank and any exhaust parts directly below it, or a heat shield. Then check the same spot from inside.
Mark and drill using the template. Use the drilling template from your heater's manual. Webasto specifies a flat mounting surface; the gasket can take up only about 1 mm of unevenness. Webasto also offers an optional mounting plate with a closed-cell foam gasket; if you use it, don't overtighten the bolts, which Webasto warns can warp the plate and damage the heater. Webasto specifies 6 Nm (+1 Nm) on the M6 mounting nuts.
Protect the cut metal. Deburr and paint every bare edge before the heater goes on. Rusty mounting holes are a slow way to lose the seal.
Mount the heater within its angle limits. Fit the gasket between the heater and the floor and stay within the angles shown in your manual. After mounting, check that the heater casing isn't touching any part of the body.
Run the exhaust. Use the supplied metal exhaust; Webasto calls for steel pipe with at least 1.0 mm wall thickness, or alloyed-steel flexible pipe. Run it falling away from the heater. If that isn't possible, drill a 4 mm (5/32 in) drain hole at the low point. The tail must not point toward the front of the van, must be clipped within 150 mm (6 in) of the end, and should discharge nearly straight down. Keep it clear of fuel and brake lines and well away from the sliding door, windows and any roof or floor vents. Webasto lists a combined intake-and-exhaust length of 2.0 m with a muffler.
Run the combustion air intake. The intake goes under the van, away from the exhaust, not facing forward and not where mud or road grit can block it. Webasto adds that if the intake hose is longer than 0.6 m (24 in), it needs an intake silencer.
Plumb the fuel. On a Ford Transit, the common route is the unused factory auxiliary port on the fuel tank sender. A Webasto North American distributor sells engine-specific connector kits that include a pickup tube, and notes some vans reach the port through a floor panel while others need the tank lowered. Otherwise, use a standpipe in the main tank or a separate small tank. Mount the fuel pump close to the heater with its outlet angled upward, on a vibration-damping mount, away from exhaust heat. The fuel line must not run downhill from the pump to the heater, and must be supported so it can't sag or be hit by road debris.
Connect the ducting. Put the warm-air outlet where it can't be blocked or touched by accident: the outlet gets hot. Draw the heater's intake air from a clean area inside the van (recirculated air), with a grille over it.
Wire it. Run a fused positive and a solid negative to your house electrical system, sized to the heater's startup current. Mount the controller where you can see it: Webasto requires a clearly visible on/off indicator. For battery and fuse sizing, see the van electrical system guide.
Prime, start and check for leaks. Prime the fuel line, start the heater with the doors open, then check for fuel weeps at every joint and exhaust leaks at the heater outlet and clamps. Run it for a full cycle and let it shut down normally.
Label the fuel filler. Webasto requires a sign at the filler neck warning that the heater must be switched off before refueling.

Carbon monoxide safety and CO alarm advice

A sealed diesel heater keeps its combustion gases out of the cabin, but only if the gasket, heat exchanger and exhaust stay intact and the exhaust can't find its way back in. CO is colorless and odorless. CDC's current guidance says people who are asleep can die from CO poisoning before they have symptoms, and early symptoms such as headache, dizziness, weakness, nausea and confusion are often mistaken for flu.

Fit a CO alarm before the first night. UL 2034, the US standard for CO alarms, covers alarms for recreational vehicles, and RV-specific 12 V units exist. A battery-powered or battery-backup alarm will still work if your house battery cuts out. CDC suggests an alarm with a digital readout, because it shows peak CO levels, not just an alarm state.
Put it near where you sleep. CPSC advises CO alarms near sleeping areas. In a van, that means the bed area, not right beside the heater outlet, where hot air can distort readings.
Test it monthly and replace it on schedule. CPSC recommends monthly tests and yearly battery changes. CDC says to replace the alarm per the manufacturer's instructions, or every five years.
Treat any alarm as real. Get out into fresh air first, then investigate. Common causes: a failed or reused mounting gasket, a loose exhaust clamp, an exhaust tip near the sliding door, or parking where the exhaust is blocked by snow or a wall.
Watch where you park. Snowbanks, tight parking spots and other vehicles' exhausts can push fumes back toward your air intake or door seals.
Service the heater. Combustion chamber gaskets and glow plugs wear. Inspect the exhaust and mounting seal at least once a season.

What people who've done it say

In a 2026 VW T6 Forum thread collecting diesel heater installs, an owner with a battery under the driver's seat and a swivel seat couldn't make a standard seat-base outlet work and asked for other routes. Replies ranged from moving the heater further back under the furniture unit to reconfiguring the battery so the duct could still exit under the seat. One poster noted the seat base was "tight, but works well."
On Wander the West, a truck-camper owner stressed that the combustion intake and exhaust belong outside the cabin, calling that the industry standard. Another member made an aluminum sleeve to protect the floor where the exhaust passes through, and a third reported three years without problems on a floor-mounted install routed underneath.
A Ram Forum member who has fitted several budget heaters for van-dwelling friends mounted one under a rear seat. He later realized he'd made two mistakes: the fuel pump was almost 6 ft from the heater, and it was pointing downward. He also reports melting a heater's gaskets by cutting power before the cool-down cycle finished, and finding algae in diesel left all summer in a clear exterior tank with a leaky vent cap.
In a T6 Forum thread on whether night heaters let in fumes, owners with Webasto and Planar units under the seat or under the van said they noticed no fumes. A mechanic in the thread pointed out that the combustion chamber gasket breaks down with age and use, which is why he prefers exterior mounting where possible. Several members said a CO alarm is worth having regardless of the heater.

Common mistakes

Taking combustion air from inside the van. Webasto's rules don't allow it, and it can pull cabin air into the burner.
Exhaust ending under the sliding door or near a vent. Route the tail to the opposite side or toward the rear, pointing down.
Reusing the mounting gasket or mounting on an uneven or rusty surface.
Fuel pump far from the heater, mounted at the wrong angle, or the fuel line running downhill to the heater.
Cutting power while the heater is hot. Always use the controller to shut down so the fan can finish its cool-down cycle. Don't wire the heater through a switch you might flip off by habit.
Skipping the CO alarm, or mounting it right at the warm-air outlet.
Forgetting freeze-sensitive gear. If water lines run near the heater duct, the heater can help keep them from freezing; if not, see how to winterize a camper van water system.

Bottom line

Choose the seat base if it's empty and you want to keep your build space. Choose an interior floor mount if you want easy service access, and an exterior mount if you have no room inside. In every case, seal the heater to the floor with a new gasket, keep intake and exhaust underneath the van, point the exhaust down and away from openings, plumb the fuel to the manual's limits, and sleep with a working CO alarm. If you aren't comfortable drilling the floor or working on the fuel tank, a professional install is money well spent.