Webasto Thermo Pro 90

I decided to do a review on the Webasto Thermo Pro 90 Heater system and for a very simple reason.. There are none available online!

Whatever the reason it may be, it doesn’t really matter. It is a great product, with a horrible online manual, of which you will need actually two if you are planning the installation yourself. The colour coding of the cable, in one of the several manuals that I found online, it gives you the wrong codes, as in, the colours of the cable do not match the name of the code given on page where the schematics are.. But fear you not, as once you see the kit, you quickly realise that you only need 4 wire out of the entire harness of cables, to actually control the unit.

Now, are you interested in having enough hot water every day for a mere $0.35 cents per day? If you are, then keep reading, as this system is for you.

As mentioned in the beginning of Gigi’s project, I didn’t want to have to deal with gas bottles, gas installation and/or certificates, and because I don’t plan to use caravan parks, the only logical solution was to use diesel power. Now before I get deep into the description of this system, I need to point out that it is an expensive setup and you also need quite a bit of room for the heater, the calorifier and two expansion tanks. You see, the Thermo Pro 90 is just one of the components required and once all the components are put together, you are easily hovering around the 3,000 dollars mark. I didn’t say it was going to be easy or cheap to build, all I said is that you can have lots of hot water for $0.35 cents per day.

You could buy a smaller system already made like the Genesis II sold by Dieselheat, for around the $2,500.00 dollars, but as you can see from the pictures on their website, the water container is small and not insulated, and that mean having to turn the diesel heater on every time you need hot water. That way, it will quickly add to the daily running costs, making it a lot less attractive.

You could purchase the smaller Webasto Thermo Top Evo water heater for about half the cost of the Thermo pro 90 and still achieve a similar result. There is also the Webasto Dual Top Evo, (possibly not longer available in 2020) where you have water and air combined into one single unit, so there are options to the cost involved in building this hot water system and it all boils down to what kind of quality and durability you are after.

Originally, I believe Webasto only intended to market the truck industry and that would explain the complete lack of online reviews also from RV owners as most of them are not aware that this system is also perfectly suitable for the RV’s (medium to large) community.

The idea here is to follow the marine industry where everything is run on either diesel or solar, as that, is not different from an RV that is purely used for dry camping. They also are the best place to purchase good calorifier for the system. A calorifier differ from a hot water boiler, because beside the electric heating element, they also have two to four separate extra inlet/outlet for water coolant coming from either the engine cooling system or, as in our case, a small diesel burner, so that the clean water inside the boiler/calorifier can be heated by either and/or together.

In my case I have a Hotpot twin coils 75 Litres calorifier purchased from ASAP Supplies (great prices and great people to deal with but they no longer sell this model) so here is a link to another supplier in the UK, connected to the Webasto, where in just half an hour (30 minutes) the water get heated to a comfortable 65° and because of the massive insulation, it stays hot for another 24 hours. Because the Webasto does use 1.14 litre of fuel per hour, having it on for half an hour per day, it gives you the running cost down to 0.56 litre per day or (around the $0.70 cents). But because the water stays hot longer than 24 hours, I only have the system coming on every second day, effectively cutting the cost in half to $0.35 cents per day

The two expansion tank are one for the clean hot water and the other for the Webasto hot coolant as, they both do expand while heating up. For the 75 litre tank I used a 10 litre expansion tank, while for the Webasto hot coolant a small 2 litre alloy tank did the job. As per instruction you also need a minimum of 6 litre of coolant running around the system, so if you don’t tap into the engine pipes (as I did), you may need another small pressurised tank to achieve that. I had an old 6 litre steel tank that did fit this job perfectly.

The kit does come with everything you need and if you also buy the marine kit, you also get a proper sealed muffler, that it is very important to have if you are installing the unit in the bin area as I did. You don’t want exhaust fume coming into the living area of the RV, so pay special attention to the exhaust design, use proper putty for muffler and test the system for CO2 possible leaks. I also have three CO2 detectors inside the vehicle..

Now to the fun part that was connecting all the wiring. In a nutshell you have all the red wires to + two brown to -. Then I did find it much easier to simply follow the pictures provided in this manual.

It also pays to remember that the Thermo Pro 90 need around 110 Watts of power (5Amp at 24 Volts or 10Amp at 12 Volts) while it runs. In the manual it does state around 80 or fewer Watts, but in my case since day one, 110 Watts has been the norm.

The system does come with one of the largest exhaust pipe in the Webasto range of diesel heater (38 mm), and it is loud. This is another factor that you must keep in consideration, especially if you have neighbours fellow RV near you. I found that having the Thermo Pro 90 coming on every day at in the early afternoon for half an hour eliminate both issue of the noise and the power consumption as my solar system at that time of the day its idling. You would definitely not wanting the system to come on at night!

The entire system is not hard to install but it does require some planning as far as where to pick the diesel and install the little pump and where to drop the exhaust gas. I also have seen installation where people did take full advantage of the power of this unit and installed several heater radiators inside the vehicle as well..

Would I recommend it? Definitely! It gives you the same convenience of a normal hot water system installed in a house, but it cost a fraction to run. Having the flexibility to heat your water, your main engine and the inside of the vehicle, all from one unit, is not that bad..

You can see in the pictures above the Thermo Pro 90, the big calorifier, the water expansion tank and the coolant metal tank..