PD 4104: Webasto C300 Heater in HVAC Circuit

[Exhaust]

Hi Guys,

I'm researching adding a Webasto C300 unit to my 4104 so that I don't need to use generator power for hot water/heat. I am planning to splice the Webasto into my existing HVAC circuit which would be able to charge the heater core for the current, original system and utilize the original fan and ducting. However, the bus is ~35' feet long, would the C300 unit be able to heat all of the coolant effectively? The 4104 system holds 18.5 gallons of coolant which I suspect would use a lot of diesel fuel to heat.

Link to the Webasto Unit:https://www.butlertechnik.com/vehicle-heater-kits-c1/webasto-vehicle-heater-kits-c126/webasto-thermo-top-c300-diesel-camper-heating-kit-41k107d-p73

Alternatively, could I create a smaller circuit in the cooling system? I am having a hard time thinking of a design which would prevent it from heating the entire circuit. I've attached an image of the 4104 coolant circuit.

Any insight is welcome! Thanks!

[richard5933]

We had a similar Webasto on our 4106. It was installed by the conversion company differently than you're planning to do. They used basically a two-zone system.

One look went to the engine and tapped into the cooling system on the side that doesn't go to the radiator. This allowed the engine to be pre-heated when necessary. A small Bosch circulating pump sent the heated water from the Webasto back to the engine. This pump was on a separate switch from the rest of the Webasto system. If you install the Webasto so that the engine and interior are on the same zone, then you'll never get the inside of the coach heated. The engine is fully exposed to the outside air and will act as a huge heat sink. All the heat produced from the Webasto will be sucked away by the mass of the engine.

The second zone on our 4106 install ran separate 3/4" hoses to a heater core which was connected to a ducted air handler to bring the heat into the coach through a number of air vents. They also co-opted the floor vents of the original HVAC system and used that to carry the Webasto-heated air to the rear of the coach.

Lloyd DeGerald recommended to me that if I wanted to update the system I'd scrap the forced air and install a number of individual toe-kick heaters inside the coach. These would be connected in series with the Webasto through 3/4" or 1" heater hose. Each is controlled by its own thermostat so that the heat can be directed to where it's needed. This is a unit similar to what he recommended: http://www.parts.rvhydronicheaterrepair.com/Heat-Exchanger-Cozy-III-EXE-103-0EX-EXE-103-0EX.htm;jsessionid=F7EDD0889BA141CB8E00B21AAB8AB4E9.p3plqscsfapp006

I'm also not sure if the Webasto unit you're looking at it is the ideal one for the application. I'd suggest asking Lloyd what he'd recommend. He knows his stuff and is really easy to work with.

There are endless ways to configure the Webasto system, but I'd suggest you don't attempt to do this through the original over-the-road HVAC plumbing unless you've got a monster sized unit, and then you'd still have the problem with the wasted heat leaving through the engine bay.

[buswarrior]

Welcome to the madness.

5.2 kW is only 17700 BTU.

All depends where you are likely to be camping, whether that will be enough heat to keep the boss happy?

The unit will be a consumer of battery power, which is fine, so long as you have taken that into account.

As noted, the devil is in the design details, you don't want to be wasting your heat/money warming the engine all the time.

As little as one 3 way valve strategically placed is a ruthless way to do both. Engine and surge tank still in the system, flow directed to house or engine as desired.

Happy coaching!
Buswarrior

[chessie4905]

Forget this setup. The factory heater motor is something like 3/4 horsepower and draws a lot of current, enough to deplete your batteries in short order.If you use a small one mounted beside main motor for boondocking, it would probably work, as the factory system had very large capacity for winter weather while going down the road. On our former 4104, I'd turn on the blower for about 5 to 10 minutes before it got too warm. I planned on adding a thermostat to the system, but never did, mainly because we travelled little in cold weather.

[Geoff]

The Webasto DBW 2010 gives you 45,000 btu's and does everything you want. But you have to design the system.  I did it and it works great. 12 or 24v.

[richard5933]

The Webasto DBW 2010 gives you 45,000 btu's and does everything you want. But you have to design the system.  I did it and it works great. 12 or 24v.

That's the same unit we had in our 4106. Worked great (once Lloyd serviced it) and was able to run on battery only if needed.