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Gas simple instant hot water

  1. May 25, 2009 #1
    [see attached diagram]I've not yet tested this! Trying to find portable instant hot water systems on line, I thought of this: A thin copper tube coil cone that can be placed over a conventional gas cooker burner. The cold water source can be a tap(faucet), raised storage container, or a pump, like for a 12v camping shower, creating a low-flow, instant hot water apparatus. The addition of the copper coil-cap makes it seem more viable. Anyone know of such a thing? Any advice before I try to make one?

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    Last edited: May 25, 2009
  2. jcsd
  3. May 25, 2009 #2


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    I don't see what the cap would do for you - is the entire coil enclosed?
  4. May 25, 2009 #3


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    I don't know if the cap is your proposed innovation, or the gas-powered bit, but there are already gas-fired point-of-use hot water heaters:
    http://www.boschhotwater.com/BoschHotWatercomHome/GasProducts/tabid/331/Default.aspx [Broken]

    I used one of these when I was in Hong Kong, and it was great--instant on, and it never ran out while you were using it. It also doesn't pull 40 to 60 A like some of the electric ones do.
    Last edited by a moderator: May 4, 2017
  5. May 26, 2009 #4
    Thanks for replies. Of course there are gas instant water heaters, hundreds of makes, sizes, volume capacities.... What I'm proposing is an apparatus that anyone with a gas cooker, or small fire, could inexpensively use, where no other hot water source is available. Also, maybe so simple a design it could be home- made by anyone with some copper pipe and tin?- for eg. And ideally more efficient than heating water in a pot on the stove/fire!? That I don't know? Just how economical in terms of heat transfer, fuel consumption and financially? The "cap" serves to concentrate the heat and circulate it around the coils, rather than just having the heat from underneath(or sides)! The coils could even be incorporated into the "cap" like a water-jacket. Conventional instant gas water heaters, are housed in casings.It would probably increase the efficiency dramatically.Here's another pic - of coils in a casing (like a prototype) (conceptually). As I think about it more and more I'm becoming aware of other design considerations and potentials... the connections, especially to the hot water pipe might need some kind of pressure valve or special fittings; that could otherwise be quite dangerous!? Of course, the diameter of the pipe, the length of pipe in coil receiving heat, would have to be determined.(the diagrams are not really to scale exactly)(& here it's not symetrical)

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    Last edited: May 26, 2009
  6. May 27, 2009 #5


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    The cap wouldn't concentrate heat nearly as well as something insulating would (it'd keep the heat in the coils and not escaping as readily). It's all about increasing surface area--something like a radiator grill over the fire (with water flowing through it) would probably work quite well also.
  7. May 27, 2009 #6
    I agree, an insulated casing would be ideal - and safer! I was thinking - simple, cheap, even home-made. An insulated 'water-jacket' would be great: that means the coils could be included/incorporated into the casing possibly achieving maximum heat transfer potential. I have no idea which material might be used for insulation at the moment except another casing spaced away from the inner? The outer casing could be interiorly insulated with some kind of fabric? I imagine the interior casing could get red hot! It'll need to be ventilated, so heat will escape. Possibly the heat capture and transfer could be improved with a thicker casing material to absorb more heat, maybe thicker walled pipes, or thinner...? The radiator idea is great, I'd like to try that sometime!Here's yet another diagram, not very helpful?, re casings and insulations:

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    Last edited: May 27, 2009
  8. May 27, 2009 #7
    This seems like a very bad idea. Yes, you can construct a heat exchanger that will work with a camp stove or fire, but you will have no control over temperature. It will take a roaring fire to deal with more than a trickle flow, and if you stop flowing water or reduce the flowrate then you have a steam generator.

    There are many creative ways to scald yourself, but I can't recomend this one. Why not make a shower tank that goes over the stove and has a thermometer. When the temperature gets where you want it you can take the tank off and hang it up for a shower.

    Alternatively you could have a thermostatic control valve on the outlet to keep the water at a fixed temperature through bypass flow. It would still have problems with steam, but it would keep you from scalding yourself!
  9. May 27, 2009 #8
    If you use a bit of automotive technology and create a supply loop into the 'heat exchanger' with a thermostat on the discharge end then once the water in the loop met the proper temperature then it would be released. The thermostat would have to be calibrated to proper temperature but that would not be difficult to do, nor would it be difficult to have made.
  10. May 28, 2009 #9
    well I agree it's potentially a little dangerous... but remember, it's instant hot water, so the operating temperature must be determined while there's flow. I suppose, with some fine-engineering, a thermostatic pre-flow system would be viable. Camp showers (eg 12v) if I remember correctly can have flow rates of 3-6liters/m! So.. the amount of heat(intensity of the flame/burner/fire) and the amount of coil exposed to it + the specs of the materials involved, fine tuned, could surely do it?! A thermostat is more than is provided with conventional gas instant geysers? I speculate! The heat source is adjustable. With this contraption, if the cold water supply is a tap/faucet, the flow rate is easily controllable(maybe too with small pump?). Without a thermostatic flow activator and no free flow - it's a bomb!(view diagram-cautiously!)

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    Last edited: May 28, 2009
  11. Jun 29, 2009 #10
    here's a similar concept (lost the diagram)X found!

    Zodi Fire Coil Water Heater
    Available Fall 2009
    The Zodi Fire Coil delivers hot water with just a camp fire. Simply connect the Fire Coil to two stacked water jugs then place the coil in camp fire. Water flows from the elevated jug through the Fire Coil and into the lower empty water jug. For hotter water just repeat sequence. The lightweight and compact Fire Coil will provide your camp with unlimited hot water. Also works with gas stoves and fire pans.
    Zodi Fire Coil Camp Water Heater

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  12. Jun 29, 2009 #11


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    Boy does this bring back some memories. We used this principal while camping back in the 60s. We had 5 gal bucket with a copper loop brazed to the side. Fill with water, but the loop in the fire and in just a few minutes you had 5gals of hot water. Of course the permanent loop on a 5gal can was a pain to hike with, but we managed.
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