You can get the Toyomoti OM-148 for about $1500
. This is a tankless water heater. This site
lists it as a diesel water heater and says it's approved for RV use, though it is a bit large for that application.
One thing to keep in mind is that diesel is pretty much the same thing as No. 2 fuel oil (reference
), so water heaters designed to run off of home heating oil should work fine on diesel. From what I've read, there are some differences like sulfur content and maybe additives, but any device designed to burn home heating oil should be perfectly fine burning heating oil, off road diesel, or on road diesel. You should probably verify this for yourself, since I'm not an expert.
Apparently, a lot of water heaters/furnaces/boilers will also happily burn No. 1 fuel oil and kerosene, though that's not really relevant if you're planning to run them on diesel. It just demonstrates that they're pretty flexible as to the fuel source.