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Old 09-03-2014, 12:27 PM   #21
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....... On all the water heaters I've worked on or replaced, if they had a provision for engine coolant heat transfer it was a simple loop thru the water heater. ............
There are thousands of boats out there with this same installation. I would think that if this was a bad plan, manufacturers would stop making these water heaters and/or installing them.
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Old 09-03-2014, 12:30 PM   #22
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After a few moments of thought, the use of another heat exchanger and a small thermostatically controlled pump could aleviate the dangerously high water temps caused by the engine coolant. Seams to be complicating an otherwise simple system, but I can see the benifits. .....
You can install a tempering valve that mixes the high temperature of the hot water with unheated water to produce a safe temperature. Having very hot water isn't all bad, it effectively increases the amount of hot water available for use.
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Old 09-03-2014, 12:32 PM   #23
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Well, yes. Like this one: SK UNI302631CN Heat Exchanger Universal / Medalist by Seakamp Engineering

As I said, if you are comfortable having a failure in your$500 hot water tank affect the cooling and longevity of your $40,000 diesel, have at it.

Got it straight yet?
I got it. So what kind of pump do you have connected to the water heater loop and how is it controlled?
Also, on my boat I have an additional loop that goes to a fan convector heater. I would guess that this is also a weak point in the cooling system and could also run off that additional heat exchanger. With my limited knowledge of marine engines/systems, I have certainly noted that the hot water loop is a weak point in the cooling system. I was thinking about adding ball valves to that loop at the engine, just in case....
I dont even know where that additional heat exchanger could mount on my 6bta, but I will put some thought into it.

I have also heard of HTP superstor water heaters being used in marine applications as well- and I have never heard of a failure in the heat exchanger in that unit- at least commercially of residentially.
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Old 09-03-2014, 12:36 PM   #24
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I think the main argument for not simply extending the engine coolant directly through the hot water tank is introducing another failure point for an engine critical system.
Technically, adding the other seakamp heat exchanger "is introducing another failure point for an engine critical system", but I do agree that is is more reliable and less prone to failure than a water heater.
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Old 09-03-2014, 12:45 PM   #25
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I have not seen any engine failures due to a faulty water heater, but it "could" happen. I also have never been hit by a meteor, but it could happen. What I wont do is lose any sleep or spend any time or money trying to avoid meteors.
I get it.

Understand it is a personality defect for me. I am an ex-submariner and an industrial maintenance engineer, so I tend to over think and over engineer most of my own stuff. Tinkering and (ideally) improving mechanical things is fun for me.
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Old 09-03-2014, 01:03 PM   #26
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I got it. So what kind of pump do you have connected to the water heater loop and how is it controlled?
Also, on my boat I have an additional loop that goes to a fan convector heater. I would guess that this is also a weak point in the cooling system and could also run off that additional heat exchanger. With my limited knowledge of marine engines/systems, I have certainly noted that the hot water loop is a weak point in the cooling system. I was thinking about adding ball valves to that loop at the engine, just in case....
I dont even know where that additional heat exchanger could mount on my 6bta, but I will put some thought into it.

I have also heard of HTP superstor water heaters being used in marine applications as well- and I have never heard of a failure in the heat exchanger in that unit- at least commercially of residentially.
As noted, I don't think you need a pump. The water will move through the loop from convection, if slowly, but that doesn't matter since you're just transferring engine heat to the fresh water in the tank. The isolation ball valves are a good idea, methinks...

I'll try to get pictures of ours and post it. Mine is just mounted next to the engine, within its footprint, so it doesn't take up much room.
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Old 09-03-2014, 01:07 PM   #27
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Technically, adding the other seakamp heat exchanger "is introducing another failure point for an engine critical system", but I do agree that is is more reliable and less prone to failure than a water heater.
You're right, there is the 2' of hose from the engine to one side of the exchanger and its return, and those could fail. However, it is visible in the ER, which the hoses in my system that run from the heat exchanger to the hot water tank most certainly are not. But that is my system. If everything is in the ER and you use good quality hose no problem. However that still doesn't tell you what's going on where you can't see it, like the exchanger loop inside the water heater. These fail as well, so all in all, I prefer isolation, and if isolated, you need an expansion tank.
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Old 09-03-2014, 01:10 PM   #28
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Isolation ball valves are a good idea. Just be sure it is in a parallel circuit, otherwise you will need a bypass valve too. Believe it or not, the "carolifier" inlet and outlet on my engine feeds the turbo housing.
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Old 09-03-2014, 01:11 PM   #29
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You're right, there is the 2' of hose from the engine to one side of the exchanger and its return, and those could fail. However, it is visible in the ER, which the hoses in my system that run from the heat exchanger to the hot water tank most certainly are not. But that is my system. If everything is in the ER and you use good quality hose no problem. However that still doesn't tell you what's going on where you can't see it, like the exchanger loop inside the water heater. These fail as well, so all in all, I prefer isolation, and if isolated, you need an expansion tank.
So what you're doing is using a heat exchanger to heat water that is then sent to another heat exchanger (in the water heater) to heat potable water?
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Old 09-03-2014, 01:13 PM   #30
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Isolation ball valves are a good idea. Just be sure it is in a parallel circuit, otherwise you will need a bypass valve too. Believe it or not, the "carolifier" inlet and outlet on my engine feeds the turbo housing.
Or, you use the all purpose Vise Grip tool for emergency valving on rubber hose. Been there, done that.
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Old 09-03-2014, 01:15 PM   #31
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Check out Alfa Laval CB series plate heat exchangers. They are small and have a very high U value for their size.

Be sure to upgrade to the needle nose or weld positioning vice grips if you choose that isolation method.
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Old 09-03-2014, 01:22 PM   #32
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Convection will not work. It is a total waste of time and money if there is no way to actively transfer heat. A pump of some sort is required, and not just any pump. I has to be able to handle the 14 psi of your engine cooling system and at least 200 degrees. this would be adding a major failure point, but without it it will not work. You may as well paint your heater black and set it in the sun, at least it would get warm.
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Old 09-03-2014, 01:36 PM   #33
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You're right, there is the 2' of hose from the engine to one side of the exchanger and its return, and those could fail. However, it is visible in the ER, which the hoses in my system that run from the heat exchanger to the hot water tank most certainly are not. But that is my system. If everything is in the ER and you use good quality hose no problem. However that still doesn't tell you what's going on where you can't see it, like the exchanger loop inside the water heater. These fail as well, so all in all, I prefer isolation, and if isolated, you need an expansion tank.
Why use the secondary loop at all? Why not just use a water heater without a heating loop and just pass the hot water through the sekamp heat exchanger? Then you could bypass the secondary glycol loop, expansion tank, etc. You also wouldn't have to worry about pressurizing and purging the secondary loop with glycol at all.
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Old 09-03-2014, 01:55 PM   #34
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Seaward sold me just the tank, which saved quite a bit of money. It was easy to replace.
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Old 09-03-2014, 02:40 PM   #35
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VP recommends adding an expansion tank in the coolant system if a parasitical heating load is placed upon the system. It adds volume to a system that was designed with only the engine cooling requirements.

Houses frequently have a check valve before the HW heater , few are found on boats.

So any water expansion goes to the accumulator already installed.
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Old 09-03-2014, 02:55 PM   #36
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VP recommends adding an expansion tank in the coolant system if a parasitical heating load is placed upon the system.
Who is "VP"?

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Houses frequently have a check valve before the HW heater , few are found on boats.
Occasionally, maybe, but there is no need for one before the water heater.

But my boat has one, it looks rather corroded and I am going to remove it. I suppose without it, heat may migrate out of it a bit into the cold water system. I will take another look at it.
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Old 09-03-2014, 02:57 PM   #37
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Sorry. Volvo-Penta.
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Old 09-03-2014, 03:20 PM   #38
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Convection will not work. It is a total waste of time and money if there is no way to actively transfer heat. A pump of some sort is required, and not just any pump. I has to be able to handle the 14 psi of your engine cooling system and at least 200 degrees. this would be adding a major failure point, but without it it will not work. You may as well paint your heater black and set it in the sun, at least it would get warm.
If the laws of physics have been suspended, yes. Otherwise, and having built miles of this stuff and can tell you that in my neighborhood, those laws still work.
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Old 09-03-2014, 03:37 PM   #39
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If the laws of physics have been suspended, yes. Otherwise, and having built miles of this stuff and can tell you that in my neighborhood, those laws still work.
Dickinson stoves and Trident submarines use convective water heating as well.
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Old 09-03-2014, 03:37 PM   #40
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You wont get enough heat transfer thru the piping to the calorifier to make any significant energy transfer without that medium being moved thru the heat sink. Sure, if you run all day you may have gained enough heat to have a nice shower, but just one. Physics being what they are, heat just wont move that fast thru your stationary coolant. Now, move that same "heated" coolant thru your calorifier, even at a VERY slow rate and you have a functional heat exchange. Otherwise not. Maybe you could move your water heater closer to your engine, it would accomplish the same thing as your non pump heat exchanger. Convection wise.
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