Webasto Dual Top Evo 6
To get the most out of my Sprinter campervan, I wanted it to be usable in all weather conditions. This meant a heater was a must. The most common RV heating solutions run off propane, but there are some heaters out there which run directly off the vehicle’s diesel fuel tank. I wanted to avoid the added complexity, space, and hassle of another fuel which would be required if I went with propane, so I opted for one of the diesel solutions.
As I have a shower in the van, I really wanted hot water as well. Luckily, there is a combined air / water heater that runs on diesel made by Webasto. The Dual Top series is made to install either inside or outside the vehicle, and provides from 6-8 kW of air heat as well as 11 liters of hot water. I looked around at a couple other options, but this was the one that seemed best suited to my needs. I went with the Dual Top Evo 6, which is the base model in the series. I didn’t really care about being able to run off shore power (which the Evo 7 and Evo 8 offer), and the 6 kW of heat output should be plenty for the Sprinter.
Unfortunately the Webasto Dual Top series is meant to be an OEM product, so if you’re a DIY’er like me, it can be hard to get much info on the product. It’s also hard to figure out how to buy it, but there’s a site online where you can find them. I ordered mine and it showed up from overseas within a few days.
The Evo 6 is quite big, so for me the only practical spot to mount it was under the vehicle where the spare tire normally lives. I took some measurements and it looked like it would fit there, although even in that space there isn’t a ton of extra room. Figuring out how you will route the air ducting is one of the first steps, as it dictates which direction you’ll want to mount the unit. For my build it made the most sense to pull cool intake air from the back of the vehicle through the gear area. The hot air would have one outlet run up to the main living area and one outlet placed in the gear area to keep air circulating back there.
Having access to metal fabrication equipment is key, as the Dual Top will need mounting bracketry made up. Note that the heater is quite heavy, even when not filled with water, so it’s important to make the mounting bracketry really sturdy. Imagine bouncing down a rough dirt road with that all that weight hanging on your brackets – it pays to overbuild here.
Next is hooking up electrical and plumbing. This is pretty straightforward if you follow the instruction manual. Make sure to put in some shutoffs in your plumbing so you can run your water system without the unit filled. A crossover between the cold supply to the unit and hot exit is also helpful (with a valve, obviously), so you can send cold water to all fixtures even if you aren’t using the unit. I’ve found that I rarely actually keep water heated, and when it’s below freezing the unit will automatically drain if it’s outside the vehicle / heated space. One additional note, if the unit automatically drains itself, it’s important that the supply pump is turned off otherwise it could drain the entire water tank! I keep my water pump on a switch, and make a habit of turning it off when not in use. I also usually have the unit drained and valves to it shut off to prevent any issues in freezing temps. Hot air ducting is pretty straightforward as well, just make sure to order the right components and minimize ducting lengths (there is no hot air distribution componentry included with the unit).
After I got everything hooked up, I fired up my Dual Top Evo 6 for a test run. It took a couple tries to prime the fuel system, but then it started up and began blowing hot air! I used the unit without issue for a couple weeks, and then it began having some problems. It wouldn’t turn on and blow hot air, and would only heat water intermittently. This persisted for a few weeks until it stopped working completely. I spent some time going through troubleshooting with Webasto’s U.S. Technical Support team, who were very helpful. Unfortunately it didn’t look like a simple issue. I ended up visiting their facility and they were able to diagnose the problem as a loose pin in the wiring harness. Since getting that fixed, the unit has been functioning great!
So what are my thoughts now that I’ve been using the Evo 6 a while? I’m definitely happy with how it performs. It will heat the vehicle up quickly when I need, and heats water relatively quickly too. My biggest complaint is related to the automatic draining function. There is an option to keep the unit in Frost Protection Mode, where it will maintain a minimum amount of heat to keep water in the boiler from freezing and draining. However, you cannot control the cabin temperature in this mode. To effectively heat the interior of the vehicle and have the boiler not drain itself, you have to keep the unit in Cabin Heat / Hot Water mode. This works fine, but it keeps the water at 70C and the Dual Top has to run a lot to maintain this water temp. It would be very nice if you could select a combination of Cabin Heating and Frost Protection modes, so that the cabin could be heated while only maintaining a low water temp.
Another consideration is electrical power consumption. I haven’t measured the actual amperage draw, but when the Evo 6 is running frequently my house batteries get run down fairly quickly. It certainly doesn’t help that the warmer I keep the inside of the van, the harder the fridge has to work as well (also electric). This isn’t necessarily a complaint, just something to make sure to keep in mind when sizing a battery bank. I have 180 AH of Lithium Ion batteries, and fully charged it seems these last about 1-2 days in sub-freezing temps if I keep the interior around 50-60 F.
The last big takeaway I have is I’d strongly consider how important having hot water really is. It’s awesome to be able to take a hot shower when it’s freezing outside, but for how infrequently I use it, cold showers would probably be bearable. If hot water isn’t a necessity, there are many smaller air heaters that are cheaper, simpler, lighter, easier to install, and likely draw less power. I think if I did it again, I’d likely skip hot water and go with an air only heater.
Overall, I’m quite happy with the Webasto Dual Top Evo 6. I would definitely recommend it if you’re looking for a solution that includes air and water heating and runs off diesel. Any specific questions, let me know in the comments!