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Old 03-01-2024, 04:10 PM   #1
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Location: New Hampshire
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Default On-demand hot water

Does anyone have an on-demand hot water heater installed? I am looking into the feasibility to retrofit an interior system (not a through-wall like most heaters) like the PrecisionTemp 550NSP-EC propane fired heater which exhausts through the floor. The downside to that unit is that it requires draining before driving in freezing temperatures, however, the idea would be to install in such a way to make that task manageable from inside the coach via access panel to unit installed in garage beneath bed.

Some additional info:

We live in the northeast and would like the ability to travel any time of year, so traveling in below-freezing temperatures is a probability (we prefer colder temps rather than hotter temps). I recognize this would only be an inconvenience when traveling in freezing temperatures, which might be "rare", but then again, it can be freezing at elevations in areas where it is generally warm.

The coach we have chosen for a near-future purchase is the Coachmen Galleria 24A with the lithium package which deletes the generator. This means that the onboard 41lb propane tank would only be serving the Truma Combi heater, which does provide hot water, but our experience with this system in past rental motorhomes is that the small (2.64gal) capacity of the hot water tank is barely enough for a quick military shower or an extended dish washing session. Adding an on-demand hot water heater to the system would allow a more confident shower (still utilizing the water shutoff method, but less fear of running out) and dish washing activities.

I understand that water use is limited, so I am not looking for half-hour long showers, but would like more than 2.64 gallons of hot water. This is especially true when we splurge for a campground that has water and sewer hookups so that we could run constant without tank volume concerns.

If you have an on-demand system installed, please let me know what you have (model number are helpful if you know) and how well it performs (or not) for you.
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Old 03-01-2024, 04:25 PM   #2
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Most on demand heaters do not work well in dry camping situations, they waste a lot of water, again, most.

We have an Oxygenics showerhead that is quite miserly for water flow, but works decent enough. The wifey and I both shower on a total of 2.5 gallons of water, measured. this includes about 2 quarts run to purge the cold water from the plumbing, a bit of a long run.

I was not a believer in the whole Oxygenics brand fan boy deal until we bought our current RV with one installed. Now I'm a believer/fan boy.
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Old 03-01-2024, 04:33 PM   #3
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Originally Posted by SteveJ View Post
Most on demand heaters do not work well in dry camping situations, they waste a lot of water, again, most.
The Galleria is equipped with a Shower Miser which recirculates the water from the hot water source back to the water tank to allow the water pipe to fill with hot water without wasting any down the drain.
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Old 03-01-2024, 07:06 PM   #4
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Hydronic heating systems such as the Rixen's Espar setup accomplish true on-demand hot water by use of water-to-water flash-plate heat exchangers from the glycol loop to DHW. You either keep the glycol loop hot at all times (using the Espar when dry camping or shore power when it is available), or you have to heat up the loop when you need it (which takes about 5-7 minutes).

I have had two vans with Rixen's systems. They are great.
Now: 2022 Fully-custom buildout (Ford Transit EcoBoost AWD)
Formerly: 2005 Airstream Interstate (Sprinter 2500 T1N)
2014 Great West Vans Legend SE (Sprinter 3500 NCV3 I4)
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Old 03-01-2024, 09:28 PM   #5
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I have Espar Airtronics D2 space heater and combination of 15l Isotemp Marine Water Heater* with Espar 5kW Hydronic. Isotemp can be heated with 750W 120V electric heater or Espar Diesel Hydronic.

You could place Espar Hydronic with Isotemp marine heater in line with your Truma.

Depending on your plumbing design skills you could design a system using Truma hot water to heat the heat exchanger in a marine water heater resulting in having on board Truma and Marine water heater volumes.
Adding a Marine water heater would give you an option to heat water with diesel, gasoline, 120VAC, engine coolant, or Truma hot water.

*Marine water heater is an insulated water tank with internal stainless steel tubing heat exchanger connected to engine coolant, often with electric heater rod. Marine water heaters are a popular option within DIY community on the Sprinter Forum. In British English it is called Calorifier.
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