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Old 01-06-2015, 04:16 PM   #1
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Heating Hot Water From Engine

I'm attempting to connect my 3208T to a new water heater that has a coil for this. Has anyone had a problem with this and where would you tap off the engine?
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Old 01-06-2015, 04:44 PM   #2
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I did a search on boatdiesel and the attached pic is what I found. I don't know that engine so I can't say if it is right. The supply port should be on the thermostat housing. Don't know where the return is plumbed.

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Old 01-06-2015, 04:54 PM   #3
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It is right under the heat exchanger on the front of my 3208 T/A. Need a pic?
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Old 01-06-2015, 08:15 PM   #4
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I did a search on boatdiesel and the attached pic is what I found. I don't know that engine so I can't say if it is right. The supply port should be on the thermostat housing. Don't know where the return is plumbed.

David
That is where it is on my 3306. Right on the tstat housing. I run mine through a heat exchanger with the hot water heater picking up the heat from the exchanger rather than by circulating engine coolant through the water heater.
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Old 01-07-2015, 06:37 AM   #5
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If you have kids visit, be sure to install an antiscald device in the FW system.

The engine circulates water at 180F+ , and that will be the sink/shower hot water temp after a short while.

OF there is room adding a couple of inches of insulation will keep the water hot for longer after engine shutdown.
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Old 01-07-2015, 09:13 AM   #6
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We have engine coolant heated water on Willy. We only have a 37hp engine and the water gets too hot.
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Old 01-07-2015, 11:38 AM   #7
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Thanks, yes my other concern is hot water tank temp getting 180 degree coolant from the engine, but was thinking of installing a temperature controlled value like a zone valve that would close when the hot water tank reached a certain temp and divert the coolant directly back to the engine. I have a similar temp control switch attached to the inverter that turns on a second cooling fan when the inverter reaches 125 degrees. Its located under a dinette seat and its internal fan needs help
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Old 01-07-2015, 11:46 AM   #8
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Mixing valves are pretty common. Sure Marine, Seattle, sell several different manufacturers.


AM100-1LF - Honeywell-Sparco AM100-1LF - 1/2" NPT Mixing Valve, Lead Free (70&#176F-145&#176F)
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Old 01-07-2015, 12:32 PM   #9
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Make sure you add a shut off valve at the engine so that when you do not need the hot water you can shut off the coolant line to the heater or heat exchanger. A marine engine mechanic asked me one time if the hot water was worth the risk of a failure in the hot water line that might cause the engine to overheat.
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Old 01-07-2015, 12:40 PM   #10
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There are both tempering and anti scald valves,

The difference is the anti scald valve will shut OFF the hot water flow if it can nor control the temperature.

Not a place to cheap out as 180F water can do great damage to skin.
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Old 01-07-2015, 02:39 PM   #11
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Unless you really need the feature of heating hot water with the main engine, I'd avoid doing it. It presents a risk to the engine AND the hot water can be too hot for safety. On small boats where genset use is rare or purposely minimized, ok it can make sense there, but precautions must be taken.

I have seen two engines ruined when coolant was changed for maintenance. An air bubble formed in the water heater loop, then when it got to the engine it air loaded the circulating pump. No flow meant hot coolant did not make it to alarm sensor. By the time operator noticed an issue, engine got hot enough to crack head, manifold and scuff cylinders.

On my personal boat, I do tap off the coolant to run a cabin heater. But the benefits of that massive amount of heat in the cabin tilts the risk/benefit equation. Hot water can be had with a ten minute gennie run, not worth putting my sacred single engine at risk for that.
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Old 01-07-2015, 02:42 PM   #12
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Just installed an Isotemp SPA 40 water heater. The installation instructions did not call for a check valve in the cold water line. Is it OK without a check valve?
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Old 01-07-2015, 03:31 PM   #13
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Unless you really need the feature of heating hot water with the main engine, I'd avoid doing it. It presents a risk to the engine AND the hot water can be too hot for safety. On small boats where genset use is rare or purposely minimized, ok it can make sense there, but precautions must be taken.

I have seen two engines ruined when coolant was changed for maintenance. An air bubble formed in the water heater loop, then when it got to the engine it air loaded the circulating pump. No flow meant hot coolant did not make it to alarm sensor. By the time operator noticed an issue, engine got hot enough to crack head, manifold and scuff cylinders.

On my personal boat, I do tap off the coolant to run a cabin heater. But the benefits of that massive amount of heat in the cabin tilts the risk/benefit equation. Hot water can be had with a ten minute gennie run, not worth putting my sacred single engine at risk for that.
Ski, what about running the coolant through a heat exchanger mounted on the engine? That is my setup and I did it that way to avoid the problem you describe.
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Old 01-07-2015, 03:45 PM   #14
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Just installed an Isotemp SPA 40 water heater. The installation instructions did not call for a check valve in the cold water line. Is it OK without a check valve?
I believe the Isotemp has a built-in check valve. At least the 6 gal. one we put on our sailboat did (along with a tempering valve). Great waterheaters, by the way. We wanted to put on on our tug, but we would have had to relocate or install a smaller heater, which we didn't want to do.
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Old 01-07-2015, 03:46 PM   #15
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our hot water does get very hot. A benefit is that we can get several days of showers while on the hook without turning on the electric heat by mixing in decreasing amounts of cold.. If I were doing it over I would add an anti scald valve at the shower control.
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Old 01-07-2015, 04:21 PM   #16
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Ski, what about running the coolant through a heat exchanger mounted on the engine? That is my setup and I did it that way to avoid the problem you describe.
That's one way to do it, it does reduce the risk to the engine. But does require a pump and head tank.

A normal direct connected loop to the water heater is not that risky at all, its just that it is some risk for little benefit. As long as operator understands the system and pays attention, it is super low risk.
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Old 01-07-2015, 04:50 PM   #17
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Most HWH have a temp vavle in that if the hot water get to a pre-set temp, the the valve closes the hot engine coolant line.....
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Old 01-08-2015, 07:43 AM   #18
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>Most HWH have a temp vavle in that if the hot water get to a pre-set temp, the the valve closes the hot engine coolant line....<

TRUE , which means folks wanting cabin heat from a coolant line will need a second line , or removal of the temp shut off setup on the HW heater .

For loads of heat to a box heater it is sometimes necessary to install a centrifugal pump to assist the coolant water flow.

A 180,000+ BTU box heater needs lots of hot water!

This gives a delight as after shut down that hot 2500lb engine can provide heat to the box heater for a good long while.Almost silent , no truck heater smell.
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Old 01-08-2015, 10:31 AM   #19
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If running at night at slow speed, my box heater can suck out more heat out than the engine is making. I see the coolant temp dropping. And of course I get less heat then, too. Not a problem in daytime as I can pick up the speed a bit.

I would not want to share the loop between a box heater and water heater, the flow would certainly be less. When I want heat, I want as much as I can get. Especially since it is free.. sort of.
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Old 01-08-2015, 09:34 PM   #20
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Pics 3208 TA

Hey Grinder,

I finally got downstairs to take pics of my 3208. The connections are right under the heat exchanger.
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