DIY high-altitude hydronic… water AND space heating in a Sprinter Van
More detailed installation notes
I wanted a system that has the reliability, robustness, and energy density of fossil-fuel heating, but that also has the option to utilize electric energy (solar, alternator, shore) energy when it is available, for purposes of space and water heating, as is shown in this comically simple diagram.
These are the actual components selected to achieve that goal. I attempted to lay out them out in a manner somewhat akin to the schematic that follows below in the image after this one.
- The “thermal storage tank w/ electric element” is how the electric (solar, grid, etc) energy gets into the system.
- The “diesel heater” is how fossil fuel energy gets into the system.
- The “air heat exchanger” is how the space heating energy is extracted out of the system.
- The “water heat exchanger” is how the water heating energy is extracted out of the system.
All the other components are just necessary evils to make this loop function properly.
My system will be pretty similar to the system below, but I’m not making the engine connection (yet, for now). In that same spot in the circuit I will have the aforementioned large insulated / electric buffer tank. Further, I will have a summer valve and a rejoining tee to bypass the fan matrix in, you guessed it, the summer.
Otherwise, everything is just “in series”. This list of items, in circuit order, is:
- Espar pump -> Espar D5 hydronic heater (w/ easy start timer and high-altitude kit) ->
- Duda Diesel double-wall plate type heat exchanger (coolant to domestic hot water) ->
- Sure Marine fan matrix with 1 Noctua fan replacing the small 2 x 2" outlet side ->
- Bosch buffer tank + electric heater ->
- Expansion tank
The physical locations of each will be:
- pump + hydronic heater: outside the vehicle under the driver
- plate heat exchanger + fan matrix + buffer tank + expansion : under the sink cabinetry
These items total up to $2520. The individual prices for these items were:
- Pump + hydronic heater: ~ $1500 (including altitude kit)
- plate heat exchanger: ~ $300
- fan matrix: ~ $430 including Noctua fan
- buffer tank: ~ $190
- expansion tank: ~ $100
Accessories. There certainly are some accessories to consider. Off the top of my head, this list includes:
While certainly not cheap, it still has a lot lower cost of failure than a Dual Top Evo 6 if any single part gives out. The most expensive part is ~ $800, instead of $3100. It was still a very hard decision, but I ultimately chose this option because I love hot water. I was trying to get as close as technically possible to a “real” shower in a Class B RV. I have no idea how close I will be yet, as I haven’t built it out yet, but… hopefully we’ll know before too much longer. The Dual Top has ~ 11 liters whereas this has about 32 liters of coolant whose energy can be converted to hot water just in time. This system will be cross-connected via the dual-wall plate-type heat exchanger to my freshwater system as discussed here.
Hopeful PROS of this system:
- Lots of heat… 5kW is a lot, almost too much even.
- Long showers… hoping for 10–14 minutes of shower time… e.g. enough for 2 people to take “RV showers” or one person to take a luxurious one from one heating.
- Safe drinking water. The dual plate heat exchanger should allow for us to still treat the 35-gallon domestic water tank as perfectly safe for drinking. See this article for rules that the solar hot water community use, but that mariners seem to ignore. I did not want to feel I was putting anyone else on board at risk nor did I want paltry drinking capacities and I want the option to easily boondock for a week or more at a time.
- Hopefully low heater cycling, as the 8.5 gallons of coolant should slow things down a lot… think cooking with cast iron instead of a titanium camp cook pot.
- Hopefully quiet enough. The heater is outside and “far” away from us sleeping in the back. The Noctua fan is like 22 dB or something crazy low. The fan that comes with the Sure Marine unit is a bit higher at like 40 dB, but hopefully that higher “boost” mode is not necessary during sleep.
- The 1440w electric element in the Bosch water heater is variable… can dial it down to save battery or dial it up on shore power. This is just perfect for maxing out a standard 15-amp x 120v outlet. I wanted the battery charger and heater to max out standard outlets. I hate things being too “special”, even if they’d be more capable. Also, this unit comes with a 6-year warranty.
- If I can figure out a way to run the pump w/o turning on the furnace (e.g. let the coolant cool to ambient), I should be able to get a couple hours of low-level heat w/o the furnace coming on.
CONS
- One has to turn the pump on in order to use hot water. This annoying, but it was the only I could find to meet the rules of the solar hot water community AND use a device with a good reputation. I’ll live with it as the means by which we keep the thermal mass of the system really high and get a kinda sorta continuous hot water system. My numbers don’t really suggest that it’s going to deliver on that, but I hear reports suggesting otherwise. I’m personally “only” banking on having 12 minute showers. This isn’t a huuuge deal as it’s probably prudent to turn the heater and pump on to bring the coolant back up to 170F, anyway.
- Lots of parts for better and worse… more, but smaller failure points.
- Install complexity is pretty high. I don’t think any system with similar capabilities is particularly easy to install, e.g. D2 airtonic + D5 hydronic + Isotemp or similar. The Dual Top Evo 6 is probably the easiest, but that came w/ the need to go to one human that’s capable of tuning it for high-altitude use and a fair bit of under-carriage work OR the heater noise is inside.
I started to put together more detailed installation notes if you’re interested in checking those out.
