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Old 03-18-2018, 09:41 AM   #1
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Using cabin heater to heat water

Replumb the original piping from the radiator to a heat exchanger to heat domestic hot water. Anyone done it?
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Old 03-18-2018, 09:48 AM   #2
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I am sure it has been done.. , personally i would not be to worried about toxic glycol but.. that is me... it tastes pretty sweet.
If you want to use it as real time shower without hot water tank, like an on demand then you need a large heat exchanger.
if you are worried about toxic stuff you can go to a non toxic coolant or build/ buy a "side arm" solar heat exchanger that has a code approved that has a non pressurized secondary water layer in between so that a primary leak would not enter your drinking water.

Good luck, later J
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Old 03-18-2018, 10:09 AM   #3
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The 10 gallon RV water heater that I put in my first bus had engine coolant connections for the built in heat exchanger.

I did a quick search and was not able to find a similar unit today. I did find Marine water heaters with that function.
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Old 03-18-2018, 10:22 AM   #4
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I've done alot of solar work, have a stainless steel heat exchanger, and a 20 gallon stainless solar tank I would mount under the cabin, small 12 v circulation pump maybe, still not sure how the controls on the bus work yet. I never have gotten it home yet to investigate, but thats another story.
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Old 03-18-2018, 11:39 AM   #5
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Search for marine water heater, many have built in heat exchanger.
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Old 03-19-2018, 12:57 AM   #6
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The general rule for ethylene glycol was, to my recollection, two walls between it and potable water.
I've been thinking off wrapping some copper tubing around an electric water heater tank. Multiple parallel runs of like 1/2 copper tubing (to equal the 1" supply) wrapped around the tank and held in place by some glue designed for this application. That glue must exist somewhere. I have the flare fittings in my junk pile. Only cost to me would be time, tubing, and glue.
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Old 03-19-2018, 05:01 AM   #7
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Yes, pretty common in motorhomes. I have this 11 gallon water heater with heat exchanger.
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Old 03-19-2018, 09:54 AM   #8
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Not that it would worried about it but I do not think that the average motor home water heater has a dual wall heat exchanger. A more expensive unit has , like bus bro's plan, has a coil wrapped around the outside. One of the issues would be that the toxic side has always lower pressure then the domestic side. Something hard to accomplish in our application.

later J
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Old 05-06-2018, 05:13 AM   #9
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Quote:
Originally Posted by joeblack5 View Post
build/ buy a "side arm" solar heat exchanger that has a code approved that has a non pressurized secondary water layer in between so that a primary leak would not enter your drinking water.

Good luck, later J
Hey J,do you have any more details on the side ark solar heat exchanger you mentioned ? I'm planning on attempting to reclaim some of the thermal heat from my panels eventually. Thanks
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Old 05-06-2018, 08:09 AM   #10
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Typical RV water heater with a "heat exchanger" is nothing more than a tube welded to the side of the tank.

Attached image is an Atwood model as used by Winnebago. (No coolant lines attached.)
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Old 05-06-2018, 09:26 AM   #11
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Hi save your, sorry I thought I could look it up real quick but I failed. Instead of only 2 pipes inside each other a third one is added. The open empty space in between is where a potential leak allows the coolant or drinking water out. If you leave air in there then it is pretty inefficient since air is a good insulator compared to most metals. I would fill the empty space with water. The disadvantage is then that it evaporates or can leak out if you turn the heat exchanger upside down.

I plan on using as air tanks that are cheap on flea bay and add an electric 24 volt element to it.. Wrapping stainless tube around it and welding that in some spots would be good enough for me but the my secondary coolant loop has already non toxic glycol.

Sorry could not be of more help.

Later j
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Old 05-06-2018, 12:03 PM   #12
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That extra pipe you see in the picture is not a heat exchanger but nothing more than a bypass for winterizing.
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Old 05-06-2018, 12:14 PM   #13
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That extra pipe you see in the picture is not a heat exchanger but nothing more than a bypass for winterizing.
Nope. That is the "heat exchanger". Picture is from my Father-in-law's motorhome. His is not hooked up. It's hooked up on mine, tougher to get a picture of, but trust me, there are (engine) coolant lines hooked to it, and my water is warm after a drive.

Note the wording and picture from an Atwood Installation Manual.

"This system consists of a U-shaped aluminum tube that is attached to the outside of the tank with welds."
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Old 05-06-2018, 12:41 PM   #14
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Strange. Not seeing how that little tube could heat the water.
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Old 05-06-2018, 01:01 PM   #15
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I was pretty surprised myself when I looked at mine. REALLY hot water (high delta T) and aluminum (high thermal conductivity) are the keys, I think.
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Old 04-26-2020, 06:47 PM   #16
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and updates on how a stock bus rear heater line could be rerouted (I'm thinking wrapping copper lines coiled around) something like this water pump with accumulator?
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