Originally Posted by THaley
Has anyone played with an on demand water heater? Electric or propane?
Electric on demand is next to impossible unless huge battery bank or generator. Propane on demand has been used a lot - EcoTemp or Triton or Joolca are main go to.
Other systems are diesel or gas fired heat exchanger based such as Espar/ Webasto Hydronic.
These all work well for showering as this is a continuous type use stream of hot water and will provide as much hot water as you have capacity. Some even are setup to draw water from a stream/lake/bucket.
The downsides of these are they require setup, combustion requires them to be mounted so they are outdoors when in use, and if you only need a small amount of hot water to wash hands, a shave, or wash/rinse of a couple dishes you will not have hot water. Also, these systems are not going to be practical for sub freezing weather camping.
A tank of hot water is nice for small use needs but then is limited to the number of gallons in the tank. For a van, 3 to 4 gallons is about the right amount of hot water capacity in terms of dedicated interior space and if it is stored at a well insulated 160 deg and dispensed via a thermostatically controlled mixing valve you have around 6 gallons worth of hot water on demand if you preplanned and turned it on.
The electric 200w 12v DC heater element is sized about perfectly for a 350 plus watt solar panel system if using a controller w managed load diversion capability. It also takes fore thought to use since 3 to 4 gallons will require 3 to 4 hours to heat up from 60 deg ambient to 120 deg.
A really great and cheap solar water heating system is the solar bag. 2 of the 2.5gal units works better than a single 5 gal. It is much easier to manage 20 pounds of water than 40. You also have more surface area for heating the water. I have measured Sun Shower bag water temps of 114F on a 50F sunny day.
Downsides are you have to use the hot water by 4 or 5 pm. The water temp drops quickly as the sun and air temps drop.
We use a combination of:
A. electric 750w 120vac and a custom 220w 12vdc element mounted in a Isotemp SPA15 Stainless water heater, and
B. two 2.5 gal Sun Shower bags
The AC is used while driving via the alternator/inverter or shore power if hooked up and takes about an hour and half to heat the water to 160 deg. About 45 mins to get to 120F.
DC is used if we know the drive is going to be 4 or 5 hours especially if traveling in the evening. The 12 vdc element can also be energized from the batteries and solar panel system. It takes a bit more than 60 amps of 12vdc current to heat water from 60F to 120F.
The Sun Showers lay flat atop the rear bumper box and are great rinse off sources.
Our only challenge is snowy winter or heavy overcast/shaded days for a couple or more days when we are not driving since we are then beholden to solar. I have been considering adding a diesel fired coolant heater and utilizing the SPA15 built in heat exchanger. This would give us the ability to heat water via the diesel heat exchanger and store the hot water in the tank for small use and late at night. We could run the diesel heater for 20 to 30 mins and have 4 gals of hot water stored.
Hot water is a wonderful luxury. Not easy to achieve elegantly or inexpensively. We have often resorted to the backpacking method of heating the water in a pot on a propane/butane stove since that works really well, lol!!