On Demand vs 10 gal tank Water Heater

[oldracerjones]

Our 2020 Entegra Esteem 27U has a water heater that runs off propane or electric, auto switching and it has a 10 gal tank. We have never boondocked and use RV parks with electrical service when we travel. With that usage profile, would I be better off with an on-demand water heater? Anybody made this change?

 

[Henry J Fate]

On demand water heating can be useful. I have experimented with a Bosch instant hot 4 gal electric. My coach from the factory only offered gas heated water using an Atwood 6 gallon tank. I looked into adding an electric heating element to the Atwood but decided to install a separate unit, Bosch 4 gallon instant.

One thing to keep in mind is that your 10 gallon tank has a heat exchanger that heats the water from the engine cooling system. Check to be sure that it is designed that way but it is highly likely. If so, it's nice to take advantage of that free hot water.

Based on several models, I elected to place the bosch instant hot in series with the stock 6 gallon gas Atwood. The water flows from the Atwood to the Bosch and then to the hot water piping in the motorhome. This gives me the ability to take advantage of the free hot water from the engine cooling system, use the Atwood as a pre-heat to the Bosch if needed and as you would like to do, use the Bosch instant hot 4 gallon electric by itself. The system works great except for the times when I am without 120 volt power and need to rely on the Atwood for gas heating. This causes the hot water from the Atwood to mix with the cold water in the Bosch causing a little inconvienence with the hot water temperature.

I did purchase a 12 volt circulator pump which will solve the above problem. It will be manually switched on/off. The circulator pump will circulate the water through both the Bosch and the Atwood offering a full 10 gallons of hot water using any of the 3 sources. This design requires some unique plumbing for RVs but is very common in commercial buildings with central hot water systems.

You can add an instant/on demand hot water system many different ways. This is one example.

I can say that even with the system without the circulator pump installed, the bosch has worked very reliably. It does need a little help when outside temps drop below 50f. The bosch I used uses a 1440 watt electric heating element.

I have not thought about installing a gas instant hot water system for the rv but have used them commercially. I would assume that a gas instant would work fine but I would always keep your tanked system available either full time or possibly use valves to take it in and out of your hot water piping offering the ability to use the tanked system when needed.

 

[Utclmjmpr]

You obviously don't boondock much or at all..>>>Dan

 

[Gary RV_Wizard]

Better off in what way? If your present gas/electric heater is delivering hot water when you need it, what would make you "better off"? Are you running short of hot water at times?

I guess I'm saying, "if it ain't broke, why do you want to fix it? Or if it is deficient in some way, tell us what the problem is so we can discuss the best methods of improving it.

 

[Ex-Calif]

I lived in houses with on-demand" heaters. The thing to know is that in most cases temperature is related to flow. If you want high flow you need a bigger heating element.

I have considered an on-demand heater for a couple reasons. The shower and vanity are right above my 6 gallon tank and the hot is almost instant. The galley OTOH has a long pipe run so to get hot water one "wastes" a lot of water waiting for the hot to show up.

You can relieve that a bit by planning ahead and using the initial cold water for something else. This of course is one of the ways to stretch the on-board fresh water.

But - when an electric on-demand heater will be useful I will more than likely be connected to shore power and city water so conservation is not top of the worry list.

As Gary asks, "What problem are you trying to solve?"

The answers can be different if you are a weekender, boondocker, full timer etc...

 

[Lou Schneider]

When I purchased my Sunnybrook travel trailer, it came with an Atwood instant hot water heater that fit in the same location as the regular tank style heater. I hated it. Like Ex-Calif said, the temperature is related to flow rate, which along with the turn-on delay and the distance between the water heater and the showerhead made it difficult to set an acceptable temperature. Seems like whenever I got the temperature just right the heater would shift it's flame size or turn itself off due to not enough flow through it and I'd either get roasted or frozen. Plus I occasionally boondocked and this made it impossible to turn the water on and off for a Navy shower.

It also used more propane than a tank style heater, 25000 BTUs (about the same as a furnace) vs. 9000 BTUs consumed by a conventional water heater. With a tank the water has a chance to absorb more of the flame's heat compared to just blowing the flame past a coil of pipe.

The heater coil ruptured during a 30 degree cold snap, the burner is supposed to run continuously at a low setting below 40 degrees to keep the coil from freezing but it ran out of propane while I was away. I replaced it with a 10 gallon tank style heater.