Underseat Diesel Fired Heater

It’s summer and you’re contemplating the van build after a nice May long weekend. With recency bias holding it’s grip tightly, statements like “it doesen’t really get all that cold around here” and “most of the year we wouldn’t need heat” are exchanged.

After a stunning sunset, the cold creeps in with night – Grand Teton National Park

Fast forward to February. One morning parked at the ski hill, your -20*c sleeping bag is cinched so tightly around your face that you might suffocate, should you not freeze first. A this moment a thought might gently float into your head

Some heat sure would be nice.

If you are planning on spending any substantial amount of time in a winter zone in your sprinter, a heater is absolutely essential. It can make what would otherwise be a meek existence into a pleasant one: leveling up what would be a rolling-storage mobile with a bed platform into a comfortable place to relax and enjoy the apres.

Ski. Ski like your boots can always dry out later. Photo: Phil Tomlinson

Last year I installed a Webasto Air Top ST 2000 w/ exhaust muffler in my 2016 Sprinter Van and have never looked back. Finishing the build in June, it didn’t get much use until November… but then I really used it. And by that I mean, I never turned it off. Continuous operating mode, all winter long. December 28 it was -24*c outside, and a healthy +15*c inside. February 16; Ambient temp –32*c, Interior tempt +15*c. You get the idea.

There are a few different methods floating around out there for space planning and installing a heater within a sprinter van, but the good ones seemed to have big information gaps. Placing the heater somewhere in the interior-build space worked for many – you can build a box within your cabinetry system, and plumb the fuel and electrical lines wherever.

Being an optimizer, I was hoping to save the living space for other lively functions, and decided to put the heater within the passenger seat podium, alongside one of my two house batteries. For a build with efficiency in mind, it really is the most sensible place to put the heater. And with the info in this post, it might be the simplest option for running fuel and electrical lines to the unit.

The finished product tucked nicely out of sight; not much to see, but that’s the beauty of it!

How to Mount your Webasto or Espar Heater under your Passenger Seat

First off, you might not be able to. This guide applies to my 2016 year model, with minimal factory accessories which would otherwise occupy the space under the podium seat. Double check that you have a full-sized podium which is effectively a square box, and not an indented version found in 2013 and earlier models (though adaptation to those might be totally possible). Next, slide that seat all the way forward and have a look under the black Styrofoam cover. Mostly empty? Good stuff. Lots of plastic rows of solenoids and such? Maybe we don’t wanna muck around in there.

Looks good, It’ll Fit. But Which Heater?

I picked the Webasto Air Top 2000 STC because of the compact size and simple control module. Friends of mine have had great luck with the Espar D2. The deciding factor was which unit I could get shipped to me up in the hinterland, which was the Webasto. Both kits come with all the wiring, ducting, fuel lines and various other accessories for the install.

How much heat do you really need? Some users have reported that heaters like the Espar D5 or Higher-end Webasto models are complete overkill. I can attest that my unit can easily keep up with temperatures in the -25*c range. My suggestion; focus less on the heater, and more on your insulation job!

Let’s get to it!

First, let’s get that seat off. You’ll need an e-Torx (e stands for external) size E14, but it’d be wise to pick up a set – they’ll come in handy for other parts of the build. Be sure to unplug the seat heater and airbag sensor before lifting the seat off. As always, lift with your knees!

To get to our wiring and fuel line ingress point, we’ll also need to lift up the cabin floor. This is easy – simply remove the torx screws at the passenger/driver footwell and lift it up in sections. Remove the black condiuit cover that runs between the seat podiums and voila! This is our workspace:

A few steps ahead, but it should look like this soon enough!

Get the Positioning Right

What we are working towards!

You’ll need two holes for combustion air in/out, and two holes for the heater fan in/out. There are some indented markings under the podium that are visible from under the vehicle, giving you a pretty good idea of where the sharp and rapidly spinning drill bit will exit as you plunge through the floor of your $50,000 van. Excited for this part? I sure wasn’t.

Before drilling, mock up the heater to it’s mounting point. The fuse panel cover on the door-side of the seat podium can be easily replaced with a carefully cut piece of plywood to do the duty. Spray paint with a colour of your choice to hide the handywork. I made use of the stock mounting place that comes with the heater, but adapted it with a few standard L-brackets to made it mountable from the side. I did all of my hose attachments PRIOR to attaching the heater brackets to the plywood panel – easier this way if you fudge up 😉

The mock-up.

Drilling Ain’t that Scary

Be doubly sure that you have the right sized drill bit for the job, my webasto required a 1-1/4” metal hole saw bit (get a kit) for both the air intake and exhaust. The holes were drilled in similar spacing of the heater unit, eyeballing where the hoses will fall with the unit positioned roughly center. The hoses are flexible – so no millimeter measurements for this one.

For the fan intake-output, a similar situation. The Webasto unit called for a 2-1/4” hole saw penetrations. For these ones, be careful to mock-up align your heater with these prospective holes – the ducting is less malleable than the metal, so your vent holes need to be within small tolerance of the heater’s angle.

Clean up the sharp edges with a de-burring tool, and hit it with some cold galvanizing compound to reduce the chance of rusting at this new penetration. Then, screw in the plastic duct covers.

Considering the Fuel Pump

It was only after I drilled into the floor that I really thought long and hard about the fact that the diesel for the heater had to get from one side of the vehicle to the other, with a few very thick beams of steel blocking the way. Oops.

Fortunately, there’s an easy solution. Remember that conduit cover that we took off? It runs between the passenger and driver seat podium. Look closely and you’ll find a grommeted hole that splices right into this conduit from below.

Just in front of the E-brake cable, you should see signs of a small opening. This is where the fuel line and pump wiring will go.

Drilling/chipping away at the plastic conduit will create enough room to accommodate two lines, one for fuel and one for electricity, to the fuel pump. Buy a perimeter rubber grommet to prevent abrasion. Both lines run from the opening, along the conduit and into the passenger seat podium.

What’s happening on the other side of this mystic conduit hole?

The fuel and electrical line runs to the pump, which is mounted to the top section of the fuel-tank rock guard. This position keeps the whole system gradually pumping upwards (you know this is important from reading the manual). No air in this fuel line.

Illustrating the fuel pump position, and drawing skills of a three year old.

At the fuel tank side, I used a number of rubber hose sizes and brass barb adapters to step-down the auxiliary fuel tap to match the size of the fuel line for the heater. Easy!

Important note about wiring: the fuel pump electrical supply comes out of the fresh air intake. Strange. I had to make a small cut in the intake hose to route this wiring back to the inside of the podium, then sealed around the wire using rubber gasket maker. With this modification, the wiring can now run internally next to the fuel line.

Thermostat and Heater Control

Using the same conduit for the fuel line and pump electrical, I routed the control wires to the drivers podium, and then out towards the galley cabinet with the final resting place being the “control panel” on the side of the wardrobe. Cuh-lean!

The 10 foot wiring harness reaches to this position next to the side window, with a little slack to spare.

Putting It All Together

You should have your fuel pump mounted, connected to the auxiliary tap at one end, and the fuel and wiring harness lines running into the vehicle through the overly described between-seat conduit. Use zip ties to secure everything. Some adhesive velcro came in handy when keeping the lines secured to the interior perimeter of the seat podium.

Hook up all the hosing to the heater. Connect the air intake and exhaust, fuel line, then the ducting for the fan intake/exhaust, all using the provided hose clamps. Once the ducting is connected and tightened down, you’re safe to tighten down the hardware to the plywood mounting panel.

We are hooked up!

To seal, I used high-temperature silicon gasket maker for the intake/exhaust. One of them hoses gets real hot!

For hose routing on the underside of the vehicle, I used blind-screw fasteners at select spots along the subframe of the vehicle where penetrations already exist. No more drilling

The exhaust Is directed behind the passengers fender to avoid any exhaust building up under the van. Also, you should get a muffler if the kit didn’t include one. It pipes down the volume to that of a silenced hairdryer.

A simple mounting rig using cheap perforated aluminum and a blind-screw fastener

That’s all!

Hopefully you have what you need to get this project done! If not, fire a comment down below about what part of this install needs more colour. I would appreciate the feedback 🙂

The Van