Toasty warm diesel heat

Winter just happened. Luckily, last week I drilled a 4″ hole in the floor of the van and installed a heater than runs on diesel from the van’s fuel tank.

Four inch hole in the floor. I had to flatten out one tiny raised section.

Espar/Eberspacher Airtronic heaters use an electric fan to push air over a heat exchanger that surrounds a little diesel furnace. The heater lives inside the van, bolted to the floor, and the combustion air intake and exhaust pipes both attach under the van. There’s never any exhaust gas inside the van, so there’s no carbon monoxide risk so long as everything’s working right.

Airtronic D2 unit and base plate, ready to install (hoses go on first)

Often, people mount the heater in the space under the passenger seat. We wanted that space for other things, so we found a cozy little space for the heater just in front of the driver side rear wheel. That area is under the bench seat and is just in front of the battery box. We need to build an extension to the battery box cabinet in that area anyway, so it made great sense to mount the fan there.

It did mean flattening out a small ridge in the van floor and cutting a corner off the mounting plate to miss another ridge. I had some cheap panel beating tools to bash the ridge down with, but I bet a piece of 2×4 wood held underneath and a regular hammer would do in a pinch. With the corner cut off the mounting plate, I had to cut the foam gasket to the new shape as well. I used a little bit of high temperature silicone sealant to fill in the cracks where the foam joined up.

Space was tight underneath the van, but it all fitted

The only thing was, the space underneath the van in that area is tight. It helped to make sure all the hoses were clamped in place to the heater before dropping it into place. Then, it was just a question of hooking everything up.

The air intake hose points off towards the front of the van. There’s a nice hole in the crossmember at that point that it threaded through with no problem. The exhaust hose has to point towards the back of the van. It ended up at about the minimum allowable length but then I added the muffler and another short hose length to point the exhaust away from the underside of the van.

The fuel line and the power cable for the pump both stretch forward towards the fuel tank. The fuel pump has to be mounted on a 15 to 35 degree angle to vertical to stop air locks from forming. The fuel line is supposed to rise gradually from that point. Mine may have a couple of dips as well as a couple of rises.

The dosing pump takes fuel from the tank all the way to the back of the van

At the fuel tank end, the fuel line attaches to the auxiliary fuel supply from the vehicle’s tank. That connector is standard on all new Sprinters.

Auxiliary fuel attachment point at the front of the diesel fuel tank

There’s a special fitting to replace the cap on the end of the aux line. It’s a Dorman 800-188 (comes in a pack of 2). The fuel hose in the Airtronic kit is a really tight fit on this fitting. If you take off the o-ring from the tip of the fitting and warm up the fuel hose in some boiling water, you’ll have better luck. Some people buy a piece of slightly oversized fuel tubing and a 1/4″ barbed fitting. They push one end of the oversized tubing on to the connector and the other on to the barbed fitting. They then push the Airtronic fuel hose on to the other side of the barbed fitting.

I knew from reading the Sprinter Forum that it can take several start attempts before the heater actually fires up. Diesel has to get all the way from the fuel tank up to where the heater is. The dosing pump that keeps the heater running is only designed to drip a tiny amount of diesel into the heater (10 hours running per gallon of fuel) so it takes a while for it to push the diesel along the pipes to start with.

Exhaust exits just in front of the rear wheel

I’m glad we bought the add-on muffler for the exhaust. When the heater starts up, it runs on its fastest setting for a while. Even with the muffler it sounds like a tiny jet engine. Without it, you’d probably wake any neighbors up.

Thermostat in its temporary mounting on the wall

We put the thermostat in a position where we can reach it from the bed as well as from the living area of the van. That way, we can reach out and switch the heater on first thing in the morning, then wait for things to warm up before we actually get out of bed.

The thermostat fitted really nicely into a Penn-Elcom 4″ recessed dish. These are normally used for flight cases. The temperature sensor is not covered at all, but the unit sits further back against the wall than if it was surface mounted. We’re using similar dishes for most of our switch panels and other mounts.

Good things to know if you’re trying this at home:

  • Most Sprinters have an auxiliary fuel line from the fuel tank. You can find it on the top of the fuel tank just in front of where the fuel filler pipe joins the tank. It’s capped off with a clip-on end piece. Inside the tank, the pipe stops a little way above the bottom so that you can never suck the tank dry by running the heater.
  • Remember to use clamps on the hose sections. The ones that come with the Airtronic are the right kind to use – when you compress them, they maintain a good clamp all the way round the hose. Ones that tighten up with a worm drive can leave a flat area that doesn’t properly seal the hose.
  • Don’t mount the pump on a resonant panel. It clicks loudly each time it doses the heater, even though it’s mounted on a flexible rubber bracket. The main chassis members are about the thickest and least resonant location I could find.
  • There are two Airtronic models, the D2 and the D4. The D4 produces more heat. I wouldn’t want any more heat in a Sprinter van than the D2 can throw out. Apparently it’s also good for the unit to run on full blast every now and again to stop it from sooting up. The D2 is hot enough on full blast. I doubt the D4 would ever feel the need to run that hot in such a small space.
  • One of the cheapest places to find these online is Heatso. If you want to try your luck with an off-brand model, you can find Snugger, VVKB and Planar brand models on Amazon at varying lower price points.

14 Replies to “Toasty warm diesel heat”

  1. Thank you very much for the great postings on your van conversion! We have a 2016 4WD 144″ high roof we are getting started on converting, and a heater is coming soon. What did you use the space under the passenger seat for? Do you see any other downsides to putting it there, other than loosing that space for other things?

    1. We wanted to keep the passenger seat space free to use as a lock box. Now though we’re thinking of putting a subwoofer in that space. The only other issue with putting the diesel heater under the passenger seat is that it’s harder to run the exhaust to a place where it won’t come in through the sliding door.

  2. This is a great site! I’m so glad I found it before I started my conversion. Which controller did you use with your Airtronic heater purchase? Heatso doesn’t list a muffler, did you have to call them to add one?

    1. Thanks Buz.

      We have the Digi-Max D1000 controller. It’s just fine for our needs, but wiring the altitude sensor to it required cutting several cables. I’m not sure, but I think the 7-day controller might be designed to plug straight in to the altitude sensor.

      We didn’t buy our Espar from Heatso. The kit I link to from this page does include a muffler. Heatso is a UK company, so they call mufflers silencers. Look in the list of parts and you’ll see “Exhaust silencer” listed.

  3. Thanks for the great write up. I’m crawling around my van now looking for a place to install my D2 in my 170 crew. I like the drivers side because it keeps me from having to traverse the van with the wiring, fuel, and exhaust. Have you had any issues with your location? Any problems with how close the intake and output are to the wall/bench seat? I like the idea rotating the furnace 90 degrees so that the intake pulls from the garage to help air flow. Any specific reason why you mounted yours perpendicular to the van like you did?

    Thanks in advance

    1. Hi John,

      If I was mounting the D2 again, I’d put it in the same location but I’d rotate it 90 degrees like you suggest. Pulling air flow from the garage would be better than the setup we have. It would also shoot the hot air into the rest of the van better.

      Hope that helps!

      1. Thanks for the writeup! Going to embark on installation next weekend! A few questions arose:
        -I am trying to understand the 90 degree change you suggested. Are you suggesting mounting this lengthwise, possibly in front of the wheel-well, with the intake facing backwards? Also, the installation manual states the combustion air intake must not be sucked in from the passenger compartment of the vehicle, are you concerned with this?
        -Also, the site offers 3 different brackets (L shaped, Floor, and Flat mounting plate). Not sure which to select to emulate your installation (and possibly the 90 degree change).

        1. Timothy, if we did the Espar install again, we’d mount it with the air intake facing backwards and the same 90 degree adapter on the hot air side to point towards the middle of the vehicle. However, it’s all going to depend on what else you plan to put in that area.

          The manual does indeed say not to take the combustion air from the passenger compartment, and we don’t. The combustion intake (thin black hose) and the exhaust (thin silver hose) are both outside the van. The air intake that’s inside the vehicle is just for the air that gets heated and recirculated around the vehicle, not for the air that’s used to burn the diesel and create the heat.

          The brackets that are shown as options for the D2 on the heatso site are for mounting the unit to the vehicle. We just used a flat stainless steel plate. It came with our heater kit, which we did not buy from heatso. I imagine that our plate is either their floor mounting bracket or flat mounting plate. I am not convinced that you need a bracket for mounting to the floor of the van anyway. It would help to dissipate some heat, and it may help with the corrugations in the floor, but I don’t think it’s essential and several people have installed their heaters without one.

          The 90 degree hot air outlet hood is probably this one on the heatso site. It looks very similar to ours.

          Have fun with your installation!

    1. Rick, the underside of the van is stock. There’s a thick layer of rubberized underbody paint. It acts as a sound dampener and probably helps prevent rock chips too.

      There’s also some “Waxoyl” style stuff which Mercedes sprays into all the cavities. That’s the yellowish color stuff that attracts dirt. Some people choose to clean this off, but it’s not doing any harm down there so long as it isn’t plugging any of the weep holes in the rocker panel.

      There were a couple of spots that we touched up with POR15 paint after we’d drilled holes or scraped some of the rubberized paint away. Those would be the black areas in the photos. POR15 is great stuff for encapsulating or preventing rust.

    1. Brandon, the heater is wonderful. It’s really fuel efficient. It’ comes up to temperature fast, even in a long wheelbase van. Running the heater for half an hour makes it easy to remove snow and ice from the windscreen if you’ve been parked overnight. Without the heater in the van, I doubt we’d have been able to sleep in it half as much as we do. Overall, a great buy.

  4. Hi. I’m having trouble locating the auxiliary fuel supply from the vehicle’s tank and I really don’t want to have to add a separate fuel tank just for the heater. Do you have any other pictures that show exactly where it goes? Thank you

    1. Ande, sorry, no other pictures. Although most newer Sprinters have the aux fuel supply, it is an optional item and so it’s just possible that yours doesn’t. Just forward of the fuel filler pipe there is an indentation in the top of the fuel tank. The aux fuel supply pipe comes out from that area. It may well be tucked right into the indentation in the top of the tank. It’s a tough place to reach. If you aren’t cursing, you aren’t in far enough. Do be careful though because this is also the place where the regular fuel supply for the vehicle exits the tank.

      It is possible to place a jack underneath the (almost empty) fuel tank, then undo the bracket bolts and slowly lower it down from the vehicle. That’ll give you access to the top to either find the aux supply or (if your tank doesn’t have one) add your own pipe to the tank. Heatso and other sellers carry a kit for adding your own pipe.

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