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Old 01-16-2015, 05:57 AM   #21
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My install is very similar. My port engine is connected to the water heater and is used as a heat exchanger, like in the picture. I had not thought of a internal failure of the heat exchanger plumbing dumping engine coolant into the water heater and thus disabling the port engine.

So Xsbank, are you suggesting installing 2 ball valves on the hoses from the engine to the water heater, one on the inlet and one on the outlet?
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Old 01-16-2015, 09:07 AM   #22
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i am not sure that having failure of the exchanger will disable the engine. Now i suppose it could water down the antifreeze enough to allow it to freeze, which would be bad. i am not sure the engine cares if it is drinking from a big tank of liquid.

It will contaminate your fresh water system with antifreeze...which in small concentrations you may not notice but could still lead to glycol poisoning.
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Old 01-16-2015, 09:43 AM   #23
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So Xsbank, are you suggesting installing 2 ball valves on the hoses from the engine to the water heater, one on the inlet and one on the outlet?
Valves at the engine take offs are pretty common if not normal in my experience.
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Old 01-16-2015, 10:04 AM   #24
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My Take

First, regarding the fittings. They appear to be Whale brand. This is a VERY common fitting on boats. Whale fittings are sold everywhere marine plumbing is sold.

Second, the wire. The wire could be solid core as mentioned, but it could just as easily be marine two strand wire from the photo. Cant see it from the photo but I'm assuming there's strain relief on the wire inlet.

The pressure valve should go down. Into the bilge is fine, its an emergency only system.

Aside from being a sorta sloppy installation, There is nothing else technically wrong I believe.
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Old 01-16-2015, 10:32 AM   #25
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There is supposed to be a hose on the pressure relief valve leading to the bilge as per ABYC (makes sense if you think about it ). I believe there should be a hose on the drain tap for the same reasons.

Double clamping is not required and is ill advised as the nipples on these water heaters are too short to support a second clamp. A second clamp would just pull the hose off.

There is no air space under the tank. The insulation is fiberglass batting which soaks up any drips, leaks etc. and corrodes the aluminum tank inside the box. This is the major cause of short water heater life.
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Old 01-16-2015, 01:12 PM   #26
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i am not sure that having failure of the exchanger will disable the engine. Now i suppose it could water down the antifreeze enough to allow it to freeze, which would be bad. i am not sure the engine cares if it is drinking from a big tank of liquid.

It will contaminate your fresh water system with antifreeze...which in small concentrations you may not notice but could still lead to glycol poisoning.
I have to agree. An internal leak in the water heater coolant loop would be opposing the internal water pressure of the fresh water system. If the engine is at operating temperature, say 180, the internal coolant pressure will still be relatively low, perhaps even lower than the fresh water pressure. If a hot water tap is full open, I suppose it could draw coolant into the system, but I don't think it would be significant enough to disable the engine. Any leakage would be dangerous for humans though.

Now, if the coolant leak is outside the water heater, the only thing that will save you is cut-off valves on both the inlet and outlet lines from the engine.

Maybe this is another reason to perform a periodic pressure test on the coolant side of the engine. The radiator-cap style of testers are inexpensive and easy to use. Test once with the cut-off valves closed to check the engine side. If OK, then test again with the cut-off valves open, the water pressure pump off and a hot water faucet open. That should let you know if there is an internal leak.

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Old 01-16-2015, 10:33 PM   #27
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You can eliminate the valves if you use a heat exchanger on the engine, then a failure of the coil in the water tank will not put glycol in your hot water, nor will it cause the engine to fail. Valves would require you to spot the failure in a timely manner but an exchanger will not. Valves just make it easier to isolate the heater, should you need to.

Definitely a dog's breakfast.
Well, yes. And no.

A additional heat exchanger is another potential point of failure as well, isn't it?

And whats a dogs breakfast?
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Old 01-16-2015, 10:38 PM   #28
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My Take

First, regarding the fittings. They appear to be Whale brand. This is a VERY common fitting on boats. Whale fittings are sold everywhere marine plumbing is sold.

Whale brand or not, the fittings dont meet my standard and IMO dont belong in an environmentally harsh area (near the hot water heater).
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Old 01-16-2015, 10:42 PM   #29
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There is supposed to be a hose on the pressure relief valve leading to the bilge as per ABYC (makes sense if you think about it ). I believe there should be a hose on the drain tap for the same reasons.

Double clamping is not required and is ill advised as the nipples on these water heaters are too short to support a second clamp. A second clamp would just pull the hose off.

There is no air space under the tank. The insulation is fiberglass batting which soaks up any drips, leaks etc. and corrodes the aluminum tank inside the box. This is the major cause of short water heater life.
Thanks for the tip on the hose clamps.

The T&P currently goes overboard. Isn't that better than in the bilge?

Air space under the tank. Are you saying I should shim up the tank a bit? OR is there space between the outer housing and the tank in which insulation is sandwiched? The insulation is a bit wet at the moment since the 'whale' fittings are leaking.
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Old 01-16-2015, 10:46 PM   #30
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I have to agree. An internal leak in the water heater coolant loop would be opposing the internal water pressure of the fresh water system. If the engine is at operating temperature, say 180, the internal coolant pressure will still be relatively low, perhaps even lower than the fresh water pressure. If a hot water tap is full open, I suppose it could draw coolant into the system, but I don't think it would be significant enough to disable the engine. Any leakage would be dangerous for humans though.

Now, if the coolant leak is outside the water heater, the only thing that will save you is cut-off valves on both the inlet and outlet lines from the engine.

Maybe this is another reason to perform a periodic pressure test on the coolant side of the engine. The radiator-cap style of testers are inexpensive and easy to use. Test once with the cut-off valves closed to check the engine side. If OK, then test again with the cut-off valves open, the water pressure pump off and a hot water faucet open. That should let you know if there is an internal leak.

Just thinkin'

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Interesting, Larry. Ok so that begs the question as to what pressure the radiator cap will allow pressure to pass through. If the HX fails in the water heater, the fresh water pump could conceivably pump water from the storage tank out through the cap on the coolant reservoir couldn't it? What pressure does an average water pump achieve?
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Old 01-16-2015, 10:50 PM   #31
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Thanks for the tip on the hose clamps.

The T&P currently goes overboard. Isn't that better than in the bilge?

Air space under the tank. Are you saying I should shim up the tank a bit? OR is there space between the outer housing and the tank in which insulation is sandwiched? The insulation is a bit wet at the moment since the 'whale' fittings are leaking.
I agree, overboard is better.
Yes, shim up the tank by putting 1/2" (or so) cleats of non-absorptive (plastic) material under the mounting flanges. The fiberglass insulation acts like a sponge and will hold water against the tank. The water will become stagnant and corrode the aluminum tank. This is much worse in salt water but often leads to leaky tanks in as little as a year or two even in fresh water.
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Old 01-16-2015, 11:37 PM   #32
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Yes, valves. If you take the engine coolant and add more loops you add more points of failure. Also, running coolant through the hot water tank runs the risk of poisoning the water supply.
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Old 01-17-2015, 12:29 AM   #33
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Interesting, Larry. Ok so that begs the question as to what pressure the radiator cap will allow pressure to pass through. If the HX fails in the water heater, the fresh water pump could conceivably pump water from the storage tank out through the cap on the coolant reservoir couldn't it? What pressure does an average water pump achieve?
Bligh,

Most pressure caps are rated at 10-13PSI and vent any cooling system pressure beyond that. I believe most fresh water pumps operate between 25-60PSI, so I think you might be right. The fresh water pressure could conceivably overpower the cap and bypass to the coolant reservoir. That would even happen with the engine turned off.

Who'da thunk that?

I have never heard of this happening though. Come to think of it, I've never heard of coolant in the hot water circuit either.

It pays to keep an eye on the coolant reservoir for a number of reasons.

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Old 01-17-2015, 08:09 AM   #34
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Thanks for the tip on the hose clamps.

The T&P currently goes overboard. Isn't that better than in the bilge?

Air space under the tank. Are you saying I should shim up the tank a bit? OR is there space between the outer housing and the tank in which insulation is sandwiched? The insulation is a bit wet at the moment since the 'whale' fittings are leaking.
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Old 01-17-2015, 08:13 AM   #35
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Yes, valves. If you take the engine coolant and add more loops you add more points of failure. Also, running coolant through the hot water tank runs the risk of poisoning the water supply.

I can see how this might happen. But I have never seen nor heard of it happening to anyone with an engine heated water heater. And they are very common. So I don't think the chances are very high of it being a problem.
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Old 01-17-2015, 09:57 AM   #36
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Old 01-17-2015, 12:53 PM   #37
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My boat had a heat exchanger that allowed me to run my heater (Hurricane - hot water) from the engine. There was also a loop to the hot water tank. The opposite occurred too, when the heater was on it would preheat the engine block and it would heat the hot water too. The builder supplied valves so that if you were at the dock/hook and not planning to run the engine, you could isolate the engine from the water tank and the heater so you would not have to run them so long and heat up a large lump of engine.

You do realize that those hot water tank coils will try to heat the engine block by thermal loop and if you can't isolate the tank with valves it will spend a long time just heating the engine block? Kind of an inefficient hot water tank.

The builder thought that running long loops of engine coolant would provide a point of failure and I agree. That's why the heat exchanger.
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Old 01-17-2015, 01:13 PM   #38
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I agree, overboard is better.
.
I and many others prefer it be routed to a catch pan so you can see if it is blowing off, indicating a problem somewhere. Our catch pan is a very visible drip pan under an engine.
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Old 01-17-2015, 02:20 PM   #39
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I and many others prefer it be routed to a catch pan so you can see if it is blowing off, indicating a problem somewhere. Our catch pan is a very visible drip pan under an engine.
T&P valves on domestic water heaters are to relieve pressure to prevent explosions of the wh. the makers of the t&p valves restrict the # of elbows and length of pipe to keep restriction to a minimum. Over board may not be best option.
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Old 01-17-2015, 09:24 PM   #40
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T&P valves on domestic water heaters are to relieve pressure to prevent explosions of the wh. the makers of the t&p valves restrict the # of elbows and length of pipe to keep restriction to a minimum. Over board may not be best option.
Manufacturers discourage lengths longer than 30 ft and for 90's, but it is not addressed by the UPC. Regardless, i have no 90s and the lenght is about 10 ft tp where it terminates overboard
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