Plumbing setup with on demand water heater

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Plumbing setup with on demand water heater

Postby joshwhite » Thu Jun 11, 2020 12:50 pm

Hi, I'm wondering if any plumbing experts can help me out.

I have created this diagram to show how I currently have my plumbing setup in my galley. I'm using a 10gallon tank on the floor of the galley with a camplux on demand propane water heater mounted in a box outside the camper. I have the drain exiting the side that will fill a 5gallon bucket I can go empty.

When I first set this up I just sorta went for it not knowing much about plumbing and used reinforced braided tubing.
I'm using a Shurflow pump, something like 2.5gal / min.

Everything was working fine and continues to work fine with this setup, however, I do get bulging of my plumbing lines, mostly coming out of the heater.
The pump is designed to kick on when the faucet is running but from what I remember, the pump continues to run to the hot water heater when the faucets are off.

I haven't put the plumbing back together since last summer and before I do I hope to get some better plumbing advice here.

I also have some random valves throughout that were placed unintelligently by me I would guess.

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Re: Plumbing setup with on demand water heater

Postby joshwhite » Thu Jun 11, 2020 1:03 pm

Also, I'm wondering how to set this up so I can easily drain all the water from the lines and the water heater.
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Re: Plumbing setup with on demand water heater

Postby troubleScottie » Thu Jun 11, 2020 5:17 pm

Not sure about braided tubing. Most likely not designed to be pressurized or heated. Often used in the fill line for a water system eg an non-pressurized gravity feed cold water line.

Better idea is PEX - designed for pressurized systems. PEX is nice; tolerates pressure; tolerates hot water; bends easily; comes in colors; lots of fittings; easily repairable with appropriate tools. A bit of a learning curve. There is even an outdoor version (green) designed for sprinkler systems, more tolerant of cold/heat/freezing. Not sure if the outdoor stuff is safe for drinking.

Most pumps of this type are designed only to be on or off. They generally do not have sensors to determine pressure or flow. One could add a timer (how??) to turn off the pump after some time if you forgot to turn it off.


Drain is a question of gravity and the ability of the water to flow to that spot. For instance, pumps often have a one-way value associated with them. A drain for the tank would have to be between the pump/valve and the tank. A drain would be a "T" with a valve. Remember to protect these valves so they do not open while towing eg contact with tall grass, brush.

The rest of the tubing means at least one more drain on the other side of the pump, lower than the lines. You want ways for air to get in (out) of the water lines to drain (fill). Obviously faucets and open quick connects serve this purpose.

Other things to consider. You might want quick connect fittings from the cabin to the water heater. Also allows you to redirect the hot water to an external shower.

You have not added a city water connection. Obviously not needed. But if you are connected to city water, something like showering is very nice and you do not have to haul all that water.
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Re: Plumbing setup with on demand water heater

Postby saltydawg » Sun Aug 16, 2020 1:10 pm

troubleScottie wrote:Most pumps of this type are designed only to be on or off. They generally do not have sensors to determine pressure or flow. One could add a timer (how??) to turn off the pump after some time if you forgot to turn it off.




Actually most pump do have an auto off in them, they run until the get to the set pressure then shut off then when the pressure drops it kicks back on. Make sure you use an accumulator, it stops the pump from cycling, and smooths out the flow of water.
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Re: Plumbing setup with on demand water heater

Postby bdosborn » Sun Aug 16, 2020 5:41 pm

Turn your tank over so the fill is on the top, then you can use the 4th hole as a drain. I used braided hose for the fill port since you can't get pex that big and it's worked fine - no pressure in the fill line (as opposed to a city water line). I used pex for everything else, no bulging or problems. I don't use an accumulator and haven't missed it. If your pump cycles it usually means you have a leak. Shurflo should have the built in pressure switch.
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Re: Plumbing setup with on demand water heater

Postby foxontherun » Fri Apr 02, 2021 8:20 pm

Good evening,
Curious about some references to "Braided" hose. Is what you are referring to like what I show in the top of the attached picture (see below)? If so, where did you (bdosborn) find braided hose large enough for fresh water inlet? What size is it? My inlet is 1-1/4".

Also, would appreciate any feedback on my schematic if it looks like I am making mistakes anywhere. Appreciate it!
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Re: Plumbing setup with on demand water heater

Postby foxontherun » Fri Apr 02, 2021 8:25 pm

My plumbing demands are only a kitchen sink and a shower. Will be using portable toilet, no plumbing hookup to that.
I plan to make my low point water line drains come out bottom side of trailer to where I could possibly use it for outdoor shower if needed. :thinking:
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Re: Plumbing setup with on demand water heater

Postby foxontherun » Sat Apr 03, 2021 9:15 am

LOL, guess a little research would have answered my question, sorry. Is this the type braided hose you are referring to: https://www.homedepot.com/p/1-3-4-in-O- ... /303209686 :oops:
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Re: Plumbing setup with on demand water heater

Postby Greg M » Mon Apr 05, 2021 7:28 pm

Your schematic looks good to me. One thing to note is many of the cheap on demand heaters are not rated for drinking water. Too much lead solder in the heat exchanger.
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Re: Plumbing setup with on demand water heater

Postby foxontherun » Mon Apr 05, 2021 7:44 pm

Thanks for the input Greg. Good thing to note on the water heater. Not sure on what water heater I will use just yet but will definitely keep the lead thing in mind. Appreciate the input. :)
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Re: Plumbing setup with on demand water heater

Postby dbhosttexas » Sun Jul 18, 2021 2:21 pm

joshwhite wrote:Also, I'm wondering how to set this up so I can easily drain all the water from the lines and the water heater.


Looking at the diagram, you can see the fill is at the bottom. You will never be able to actually fill the tank this way.

Move your fill to almost the top, and vent lines just above them, or you will end up with a non functional system.
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Re: Plumbing setup with on demand water heater

Postby dbhosttexas » Fri Jul 30, 2021 9:59 am

Sorry, I don't have the tools loaded to do a graph for you, BUT...

Your pickup at the bottom of the tank looks right. Stay with that, fed to the pump, then out with a Y fitting, adjust your pump with the lowest practical pressure with highest flow for your system, this will require some post install fiddling. Follow your pump MFG instructions.

Splitter / Tee is good, Y is better for flow. One side to the cold water side of your faucet is fine, other side to the heater is good as well, and of course out back to the hot side of the faucet again, good...

Make sure your fill line and tank vent are above the highest possible point for the water in the tank. It is best to have the vent as a tee in line with the fill, and run the vent line above, considerably if possible, the level of the filler. That way overfilling doesn't push water up and out of the vent.

A properly setup pump will kick on with low pressure, and off with high cutoff, so faucet closed off pump shuts off, faucet on pump kicks on.

You show a drain from the faucet. I assume this is a gray drain from a sink. You may want to run that to a gray water tank or risk facing the wrath of park hosts or rangers....

The higher the flow rate of your pump, the larger diameter line you will need, the higher the flow rate, the faster your tank gets empty. Chose wisely.

Braided line tends to be rated for higher pressures, but watch your temp rating on your lines. PVC at high temps does not like high pressures as it tends to get soft and weak. I have some allegedly high temp vinyl tubing used for my ensuite plumbing that will run hot, ish water to the shower. I figure if it is at the max temp I am willing to have hit my body, it won't get the tubing too hot. I would pick a higher temp rated material if I were plumbing like you are though as I would tend to turn the heat all the way up on the water heater and mix the water at the faucet... More home like...

Good luck, and keep us posted on your progress!
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