The key component in the on-board hot shower is the heat exchanger. It has to be efficient enough to allow for instant, unlimited hot water. In my opinion, a plate heat exchanger is most suitable. It has compact design and is resistant to corrosion.
Weight added: 10 lb / 4.5 kg
It is necessary to install the heat exchanger in the engine compartment near the heater pipes. The best location for me was a place under the battery tray. I was installing the dual battery tray at the same time and a plate heat exchanger fits neatly when bolted upside down under the auxiliary battery. I am sure that the standard, single battery tray may very well serve the same purpose. Other possible place for the heat exchanger is a firewall on the passenger side, but unfortunately, that requires the drilling. I did not like this idea, because in my projects, I tend to avoid any drilling in the car body.
I was not sure which of the heating hoses should be connected to the heat exchanger, input or output. It seems that it does not matter in Jeep JK. Hot coolant fluid flows freely in both hoses and it does matter whether heating in the cabin is turned on or off. I decided to use the lower hose, as the more convenient to attach to a heat exchanger without cutting it, just in case, I need to reconnect it. It is important to note that liquids should flow in the opposite directions in this type of heat exchanger in order to achieve the best performance. Based on the information I received from the manufacturer there is a 17% performance loss when fluids pass in the same direction.
I wanted my hot water system to work without opening the hood. I found two existing holes in the frame behind the front bumper. This is the place where I mounted quick release connectors for quick shower hose attachment.
I had already owned simple camping shower with water pump. It was definitely the good fit for this project. I bought water hoses, added quick-connect fittings and my system was complete. During the first test, water became so hot so that it made washing hands simply impossible. I had to purchase thermostatic mixer valve to regulate water temperature in the shower. After first month of using, the pump that came with the camping shower proved to be not a solid construction. As the replacement, I decided to purchase another electric submersible water pump.
I use plastic container as the water tank when using a shower. When container is emptied, it is used for storing showerhead with all the hoses. Usually, we use water from our water tanks. When taking shower, engine has to be on for the heat exchanger to work properly. Thermostatic mixer valve allows adjusting water temperature based on personal needs.