Reposted this description of the simple shower water heater so I can find it in the future.
The design is for heating shower water just before showering. It is not suitable for having hot water available all the time. I only need warm shower water. Do not need hot water at the sink. Clean dishes with cold water and soap.
Completed the design using the "sprint2freedon" suggested use of a 800 watt (actual 750 watts) Sous Vide cooking water heater. The Sous Vide machine can be bought for $44 to $70. It includes a 120 v AC heating element, water circulator, high temperature shut off, thermostat, digital temperature display and easy to program temperature/time setting. Everything you need to heat shower water for a conversion in compact inexpensive unit. A Sous Vide machine is used to cook food in a kitchen.
I had made a mistake building my existing shower water heater using a RV propane to electric conversion kit. The 6 gallon tank is too large. Best to heat 3 gallons of water instead of 6 gallons to cut the time and energy usage in half. So looked for a container that had the correct dimensions to hold 3 gallons with the water level between the high and low water level limits of the Sous Vide machine. If two people need to shower you just repeat the process.
The end result is a portable water heater that normally is my trash can. Remove the garbage bag when I want to heat shower water or cook. All the parts except the hose can be stored in a Cabela's plastic ammo can when not in use. The cooler lid is discarded and replaced with two UHMW covers. One side has holes for the Sous Vide machine and the pump. Other side has two large paper clips to hold the ZipLoc freezer bag to hold the food when cooking.
The hose is connected to the pump with a garden quick disconnect. The valve is a radiator fill nozzle to provide a on/off at the nozzle and provide full flow water flow. The full flow nozzle helps prevent water overspray onto the van floor. Much less overspray than a spray nozzle.
The design heats all the water in the container to the desired shower water temperature. That eliminates all plumbing and hot/cold water mixing. No potential water leaks.
The unit heats 3 gallons of water from 61 degrees to 95 degrees in 20 minutes and uses 6% of my 255 amp-hr house battery capacity or about 15 amp-hrs. On a sunny day I can shower in the morning and be back to 100% SOC that day. I have enough excess solar power from my 300 watt panel to heat the water. The other options are to use my vehicle powered inverter to supply the power with the engine running or shore power. The time to heat the water depends on the initial water temperature and the desired shower water temperature.
Some comments on the design:
1. Unit is portable and can carry 3 gallons of water using the cooler handle.
2. You can shower any place you have access to 12 volts DC for the pump. Now building a small portable 12 volt battery with charger that has a cigarette lighter receptacle. We get power outages at our home on 5 acres. The portable shower water heater will also be used in the house. Heat water in van and carry the cooler into the house for showering.
3. The cooler can be carried to a water source such as a stream, lake or faucet so conversion water does not need to be used for shower water.
4. The cooler without the lid is ideal size for my use as a waste basket.
5. The water heater can be used for cooking with the Sous Vide machine. The plastic is rated at 176 degrees for continuous hot water.
6. Any water left over after a shower can be pumped back into my existing 6 gallon shower water tank. Same if cooler is used for cooking. When done cooking, pump the water back into the shower water tank.
7. Cooler with handle can be used to move grocery items from house to van and from van to house after a trip.
8. Cooler with water can be placed in the sun to heat the water to reduce house battery power usage.
9. Cooler can still be used as a cooler by removing the original lid hinge circles from the lid.
10. If van house battery SOC is low you could always heat water on a propane stove and mix it with cold water.
11. Design eliminates plumbing and hot/cold water mixing.
12. Very simple to build. Only 3 plastic parts to fabricate from a plastic cutting board. The rest of the parts are standard purchased items.
13. Size of cooler allows storage in small space.
14. Igloo cooler can be used as a camp seat.
15. System is light compared to other choices.
16. Simple so less chance of failure.
17. Water is not under pressure so less chance of water leaks.
18. With a portable 12 volt power pack you can shower wherever you want.
19. Cooler can be used as a bucket with water heating stuff removed.
So the result is a light weight inexpensive portable system to heat shower water. Material costs are between $190 and $225 depending where you buy the components.
I have a set of 6 CAD drawings that detail the system, lists parts costs and where parts were purchased. The drawing set includes a 24 x 36 cooler assembly drawing, four 11 x 17 full size parts drawings and a 24 x 36 drawing of the portable 12 volt power unit. Smaller drawings have a full size left side cover pattern, a full size right side cover pattern, a pump assembly drawing and a hose assembly drawing. All the information needed to built a water heater. PM me if you want to buy a drawing set for $30 post paid in US.