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Thread: Cycle hot water into water tank ?

  1. #1
    Seglare Sven's Avatar
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    Cycle hot water into water tank ?

    We too sin. We have probably powered 24 hours in our last month of "sailing".

    We have an 80-gallon water tank. We have a 6 (?) gallon water heater tank.

    What I'm thinking of doing is installing a diverter so that we could pump that water back into the main water tanks as we go, to heat up that large volume and not just the water heater tank. The purpose is two-fold; to have warmer water than just plain cold accessible more of the time and possibly also to help heat and dry the cabin itself.

    Thoughts ?



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  2. #2
    Sustaining Member eknebel's Avatar
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    I have thought the same thing myself, but with a additional heat exchanger in the loop with a fan(just like in a car) to heat the cabin air. That way you could really heat the cabin. If you add loop with an additional separate pump to circulate the water from the heater tank itself thru the heat exchanger(not the water tank), it would be at engine temp in about 45 minutes(my boat). It would take about 10 hours of motoring to bring the entire 80 gallons up to engine temp, so most of the time you would have lukewarm water, unless it was a long haul. The question with heating up the entire system is are the hoses and tank rated for 170 degrees? Perhaps a added heat exchanger/closed loop would be the safe way to go. You could just add the heat exchanger into the engine coolant, but then wouldn't have the heat bank of the six gallons of water. I am not sure how long that would heat the cabin, my guess is not long, that's why you don't see it on boats...
    I haven't done it yet, but if you do it, please post with the results.
    Ed Knebel
    E-30+ 1980
    "Blitzen"

  3. #3
    Principal Partner sveinutne's Avatar
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    Hi Sven,
    I am heating my 80 gallon water tank by cooling the gear transmission and hydraulic fluid for the transmission. I have never motored for a long time, only one or two hours at the time, but the cabin heats up some degrees, so it is not so cold to enter. I am thinking about how I could use more of the engine heat to warm the cabin even more. But it is very cold in Norway, and you might not need too heating that much, so to have a valve to adjust the amount of heating would be nice to have I think.
    Svein Utne
    Ericson 41 -- Hull # 26
    svein_utne@hotmail.com

  4. #4
    Sustaining Partner
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    I have given these thoughts some consideration myself, and will probably try it. It doesn't concern heating the holding tank water, as it does heating the cabin. Short of a thermal dynamics debate, a big bag of hot water is not very "efficient". So, a common heater core from an automobile, (I know a new one for an older Ford truck is around 30 bucks), build a small box for it, with a 12V fan behind it. Naturally running hoses to it of course. Small, low maintenance, and hot. I know the heater cores are copper, and they degrade, etc. But thirty dollars? That's a tip for a waitress, I could replace it every year with a well thought out box.
    Dissensions?

  5. #5
    Principal Partner Lucky Dog's Avatar
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    I read about this somewhere, http://www.heco.net/red_dot_heaters.htm They make commercial grade heating coils for trucks. I think I had one in my 70's Chevy van.
    "The greatest tragedy in life is people who have sight but no vision." Helen Keller

  6. #6
    Innocent Bystander tenders's Avatar
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    What clp says - the easiest, fastest, least expensive, and time-tested solution.

    Unless you enjoy the taste of antifreeze, I would not want to risk tainting my potable water supply by running engine coolant hoses through it.

    If you want 80 gallons of hot water, lash a GE tank to the mast! I'm sure stranger things have been done.

  7. #7
    Senior Moderator Loren Beach's Avatar
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    Lightbulb

    Quote Originally Posted by Sven View Post
    We too sin. We have probably powered 24 hours in our last month of "sailing".

    We have an 80-gallon water tank. We have a 6 (?) gallon water heater tank.

    What I'm thinking of doing is installing a diverter so that we could pump that water back into the main water tanks as we go, to heat up that large volume and not just the water heater tank. The purpose is two-fold; to have warmer water than just plain cold accessible more of the time and possibly also to help heat and dry the cabin itself.

    Thoughts ?
    -Sven
    Couple of thoughts come to mind. If you have a large amount of warm water in your stock plastic rotomolded drinking water tank, you need to check with the tank maker for the thermal limits of calculated strength for that material. It could, after a longish time motoring, get very hot - like 160 degrees.
    Also, if you are not running new clean water through that tank very often, the heat provides an enhanced growth medium for small plants i.e. microorganisms. ( Even at "temperate zone" ambient temps in the summer we have to flush and wipe down our 38 gallon tank interior about once a month if we are not using the boat for a while and cycling lots of new water into it. )

    As for heating the cabin, note that there are well-engineered heater units that run off of the engine coolant lines. We have a Heatercraft fan/radiator unit under one settee. http://www.heatercraft.com/
    (The current model 500-H looks like the one I installed.)
    It's in series with the hose runs that go to the hot water tank coil. It puts out amazing amounts of heat when the engine is under load - way more than we can use. Of course, when you shut down the engine, no more heat from that source.

    If you have a large tank it could indeed act as a mass heat storage, and with a 12 volt pump to circulate the warm water thru a fan/radiator system, it would warm you a little bit, but only for a while.

    Stay warm.

    Loren
    Last edited by Loren Beach; 08-06-2012 at 08:44 AM.
    1988 Olson 34 #8
    Sail # 28400
    Betamarine 25 (new 2018)
    Fresh Air
    Portland, OR USA

  8. #8
    Principal Partner sveinutne's Avatar
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    I needed to cool the hydraulic fluid and the transmission units, and under gentle load it will be about 5 kW of heat that needs to be removed. The water tank is holding about 10 degrees Celsius during the summer, so even after an hour of motoring the water is only between 20-30 degrees. I guess the heat lost to the cabin will increase a lot if the temperature in the water goes up till 40 or 50 degrees, so I do not think it will ever get any higher. The number of hours the water has been above 20 degrees is so few that the growing in the tank should be less then what is normal in most places in the US.
    When I am sailing, there is no heat, so I have been looking for other ways to heat the cabin. If I can wait a year or two, I think some alternatives will come. Cold fusion might be one of them.
    http://www.slideshare.net/tylervan/lenr
    So the future looks bright if we can hang on for a year or two.
    Svein Utne
    Ericson 41 -- Hull # 26
    svein_utne@hotmail.com

  9. #9
    Principal Partner
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    The ubiquitous "bus heater" from RedDot or Heatercraft is the way to go to heat the boat underway. I can't see a reasonable way to control the heating of the water however. The simple way to accomplish what you want. Install a return hose from your hot water output to the storage tank with a three way valve. Flip the valve and run the water system pump. It'll just return the heated water to the main tanks. You could install an independent pump to do this but to see if it works the pump you already own should do it. I wouldn't be too concerned about coolant contamination of the potable system, there is already a coolant loop in the waterheater as it is.

    RT
    Rob Thomas
    Wakefield, RI
    1983 Ericson E38 "Ruby"
    "I purchased a boat because setting fire to $100 bills was not an efficient enough way to dispose of them...."

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