Additional Thoughts on Tankless Water Heaters - Consider this

[Gary Hatt - Publisher BCM]

On Facebook, someone recently mentioned they bought a heated fresh water hose with an inside diameter of about 3/8, and said they were having problems getting hot water from their tankless water heater.  Several people commented that tankless water heaters need a pretty high flow rate to turn on the burner, which, when boondocking for a few days, can be a concern with a limited water supply.  This was mentioned in a previous thread a few months ago, but is worth mentioning again.

In my Eagle, with an Aqua-Hot system, I generally turn on the diesel heater for 5-10 minutes before a shower when dry camping, so it is not on all day, unless I need the cabin heated too.

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I currently have a tankless water heater, but I want a tankful water heater now. 

I usually use only a trickle of water for everything when boondocking, but it's not enough pressure to activate the tankless water heater. So for hot water, it has to be on full blast, wasting 6 seconds (4.5 seconds to activate) of water flow until the hot water finally comes out of the faucet. And then if I want it to continue having hot water, I have to keep it on full flow. So, just doing the dishes would waste a lot of water. I just have water tanks, not a city water connection, so water conservation is essential to me.

Because of all that, I've added a hot water loop that feeds hot water back into my tank so it keeps flowing and keeps the water heater activated.

But I still find myself just wanting a tank to keep it simple.

[Jim Blackwood]

My solution is a dual mode water heater, both propane and electric. Normally I will just leave the pilot light burning (none of this electronic igniter business) which does a great job of keeping the water in the tank at a comfortable temp for washing hands and dishes at any time day or night. The cost of running a pilot is inconsequential, especially when compared to the benefits. Then a few minutes before heavy hot water usage I fire up the main burner and switch on the electric heating element. That gets the water hot fast and when I hear the burner kick off I head to the shower or turn on the washing machine. The dual mode does a good job of keeping up and stretches out the hot water that is available, allowing the use of a 6 gallon water heater instead of something larger. Of course this solution means you have to have propane on board, but I like propane. It's a versatile energy source. I'd probably have it on board even if the water heater is all I used it for.

To get the same result with an all electric system, I guess you'd need a fully programmable controller, in which case you'd have a way to set up water temps at various times of the day or week, but it seems like that would tie you to a somewhat rigid schedule, say for showers and doing laundry. That may be ok, but I wouldn't be a big fan. Maybe there's a controller that would let you program it so that at the touch of a button it kicks on the water heater for 15 minutes or so and beeps at you when it gets warm, but I suspect that'd take some doing to set up.

Another thought about passive energy collection maybe for boondocking and such, is that as long as you could set up a collector at ground level you might be able to make use of a thermosiphon loop tied to your water heater. It would be tricky due to pressure issues, since thin membranes in the collector at lower pressures are going to conduct heat quicker but the potential at least exists whereby your water heater tank could take heated water from the collector. Those who have used one of the commercially available "solar shower"s know that a couple hours in the sun can get the water quite warm, even in winter provided you keep the wind off it. I do like passive collectors but they are never simple and cheap to set up. Propane is pretty much both of those. I am a fan of passive energy collection systems, whatever form they take. I've known of heat collector units that used an air thermosiphon system for instance. Not really that useful in an RV but OK for other purposes. Eventually I expect to have solar panels on the roof. Just not the ones that are presently common.

Jim

[Gary Hatt - Publisher BCM]

In my previous bus, I used the electric and set it to a 30-minute timer, and crank it up about 30 minutes before each shower. If I need hot water faster, I use both propane and electric at the same time.