Using a hot water tank/heater with a heat exchanger


New member
Has anyone considered using or is currently using a hot water tank/heater with a heat exchanger like is used in marine applications? It seems to me that these water heaters are a food match with the Sprinters auxiliary coolant heater used for heating the engine and cab.

With this setup you could preheat water before you leave on a trip or while at a site that has connections using the hot water tank electric heating element and use heat from the engine to heat the tank while driving and the sprinter auxiliary heater when parked at locations without electrical power connections using the hot water tank heat exchanger. And since the tanks have good insulation once heated the water should still be hot enough the next day for a warm shower.

Here is a good review of some different brands of this type of water heaters:

Here are some of the different hot water tanks/heaters with a heat exchanger (Isotemp was the best rated brand in the above article):

I assume it would be best to mount the tank inside the van so that freezing wouldn't be as big an issue for the fresh water connections. And it would be good to mount it close to the sink and/or shower. It would also be best to mount it as close as possible to the auxiliary heating unit and/or engine to reduce the length of the hot coolant lines, thereby reducing heat loss and flow drag losses.

Here is a page that explains some of issues of Hydronic Heating Systems.


New member
I've considered them, but haven't looked all that much at them yet. I've been wondering about going tankless and using a heat exchanger only for hot water. This would mean either the engine or aux water heater would need to be running to have hot water. Looking at the prices for some of these units it may be cheaper to go with one of the Isotherm Basic units. Looking at the dual exchanger units one could hook both heat exchangers in parallel to the engine / aux heater and have twice the recovery rate. :idunno: Who knows what is best.


New member
Good idea! I've intalled several hotwater tanks on boats; they work great.
My favorite is a SuperStor available from Defender Industries (DI is the best source for mail-order discount marine grade-parts if you can't buy wholesale). Indeed, there are a whole lot of RV parts/systems that should be replaced with marine equipment. Battery charging systems for sure; both from AC hook-up and from the alternator. After cruising for 10 years we are new to RVs and are repeatedly amazed at how flimsy and primitive the RV counterparts are.
DO WATCH OUT for the water temp!!! (Probably why they do not install them on RVs; boat builders assume their customers will figure these things out).
The engine will heat the hot water tank to 180 degrees...way above the 150 degree safety valves on most domestic hotwater tanks. You need to be cautious and use cold water mixing; not for the absent-minded. And be sure to warn guests! I'm installing a SuperStor 6 gal. tank in our new LTV as soon as we get it home (along with a Xantex 40 amp 3-way smart battery charger, Balmar H-O alternator w/3 stage charger and a Link 2000 battery monitor)


New member
I've installed a Force 10 Marine water heater in my homemade Sprinter RV. Currently it runs off 110V shore power. It has a heat exchanger built in to utilize the vehicle's cooling system to heat water while driving.
My question is where do you tap into the cooling system? And can you install a diverter valve (when you don't want to heat water within the Force 10)?
A diagram, parts list and/or installation instructions would be great.


New member
I am about to try the same thing. Where did you mount the Force 10?
I am looking at the outside of frame behind sliding door, a bit tight at 12 inches wide vs Heater at 13.



New member
I mounted it inside a cabinet beneath the sink within the vehicle. I wanted it to be close to the interior plumbing and I didn't want to have to insulate it.
Do you know where you're going to tap into the system?


New member
My question is where do you tap into the cooling system? And can you install a diverter valve (when you don't want to heat water within the Force 10)?
An instalation I helped with a decade or so ago we tapped off the heater lines. We used Ys, and also put in valves to allow shutting off engine water to the heat exchanger. I remember something about using a circulating pump if the distances was over so long, but I don't remember that distance. I'm sure if the hot water tank was in the forward half you would be fine without one. As you route the hoses through the fire wall or van's sheet metal, remember to grommet and support your hoses to keep them from abrading and developing a leak.

- Bryan


'02 140 Hi BlueBlk Pass
Take a look at this thread for tapping into the coolant system:

Also, look at the installation manuals for the Espar heater for additional ideas:

And if you already have the auxilary rear heater, those lines are both closer and more accessible.

I am not sure why there would be an issue on needing an additional circulation pump for the relatively short distances at issue here, comparable to the rear auxilary heater already offered without the need of an additional circulating pump.
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New member
You will find instructions that suggest an auxillary or boost pump, but most likely you will not need one. On our boat the hotwater heater is 15 feet away from the engine and there is plenty of circulation.
Besides, minimal circulation would be GOOD. Coolant circulates at 180 degrees F which is too hot for a good domestic supply. Don't worry about boost unless you cant heat the water after a 1/2 drive.
HERE IS A SAFETY NOTE: Don't drink water from the hot tank after installing a heat-exhanger (you'll be tempted to make tea and etc. because the water is so hot). The chances of a leak of coolant into the hot water are very very remote; but the consequence of ingesting even a small quantity of antifreez can be leathal (it's never a good idea to drink form the hot tap anyway since so many domestic hot water systems are full of lead pollution due to older soldering methods).


New member
My 2014 era 70A water heater has the exchanger built in but not connected. Seems like a small job to connect it to engine cooling. Might have than done within the next few months. Worked great on the boat. 180 degree water, will be hot in the morning with no propane.


Strongbox Sprinter
Hi Viking did you connect your water heater to the cooling system?

I am trying to find out where to cut in to the system in my 2006 Sprinter? so I can connect to my waterheater with heat exchange?

The water heater works also on 110 volt but since I mostly will boon dock the 110 volt function is not ideal.

Any help will be appreciated.


Active member
If you shut the engine off in the evening, go to sleep for the night, how will the water temp be 180 deg. F the next morning?
The radiator will "radiate" all of the heat stored in the heat exchanger back out into the air...won't it?
Inside the hull of a boat, would seem like it would store the heat for a lot longer air exchange radiator.
My my boat engine always cooled down to pretty much stone cold overnight even with no sea water pumping into the
engine heat exchanger, and the engine was in a pretty tight box.
Air could circulate in the bilge all night and cool things down.
Small Ford 289 V8/Vovlo Outdrive in a 23 footer.

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