Diesel Night Heater Install: Under-Van or Driver's Seat (VW Transporter)

The Problem

You want to fit a diesel night heater (e.g. Webasto, Eberspächer, Autoterm, or a budget Vevor/Chinese unit) and are undecided between mounting it externally under the van floor or internally under the driver's seat, weighing noise, access, and installation difficulty. There is no existing heater to diagnose — this is a first-time fit. Before buying, confirm your chosen heater's bracket and duct dimensions match the mounting location, as these vary by brand and output rating.

Solution

1. Mount the heater externally under the van using the factory bracket space. On VW Transporters this is the location VW intended for an under-floor heater — confirm which chassis generation you have (T5, T5.1, T6 or T6.1), as the exact bracket position and available clearance differ between them. If you are unsure, offer up your specific heater (Webasto, Eberspächer, Autoterm, Vevor or other budget unit) to the space before committing, as bracket footprints are not interchangeable between brands.
   • Under-seat mounting is valid if you prioritise easy access for servicing, but under-van is the more common choice and keeps the cab clear.
2. Jack the van and crawl underneath to fit the heater and bracket.
3. Cut floor holes for the ducting using a hole saw matched to your heater's specified duct sizes. On most kits the combustion-air intake uses the smaller duct and the warm-air outlet uses the larger: a 60mm hole typically suits the smaller air duct on lower-output heaters (around 2kW), while a 90mm hole suits the larger warm-air outlet or higher-output heaters (around 4–5kW). Always check the duct diameters printed in your specific heater's manual before cutting, as these vary by brand and output rating.
4. Spray all cut edges immediately with cold galvanize spray to prevent corrosion before fitting anything.
5. Push a duct joiner/bulkhead connector through each hole and bond it in place with Sikaflex sealant, ensuring a fully gas-tight and watertight seal.
   • Exhaust gases can enter the cab surprisingly easily through unsealed floor holes — do not skip the sealant step.
6. If using a budget Chinese heater (e.g. Vevor or unbranded), replace the supplied exhaust clamps and fuel pipe with better-quality equivalents before running the unit.