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post #1 of 9 Old 05-25-2013 Thread Starter
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Diameter of Diesel Water Exhaust Pipe

Wonder if someone can help me here....

I am connecting up a hot water heater. The current tubing from the diesel for the water exhaust is 3/4". I have a bunch of 1/2" tube lying around to run to the heater's exchanger.

Does it matter to the engine to step down to a smaller size tube, or is it important to keep to the 3/4" (i.e. have to by more tubing).


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post #2 of 9 Old 05-25-2013
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Re: Diameter of Diesel Water Exhaust Pipe

I would stick to the 3/4" to reduce back pressure on your pump. you are adding a longer line with more connection this will add some resistance in and of itself. That said you should be using the coolant side of your engine water not the raw water. Most water heaters are not designed to have raw or salt water in them. It works but you will be replacing the heater every 4-5 years if you do.

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post #3 of 9 Old 05-25-2013
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Re: Diameter of Diesel Water Exhaust Pipe

Actually.. I believe most WHs are 1/2" heat exchanger connections. the "loop" from the engine would be circulation of coolant rather then actually pumping. My boat, the lines are 7/8 ID and reduced to 1/2" and it works too well!

Denise, Bristol PA, Oday 30. On Tidal Delaware River, Anchor Yacht Club.
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post #4 of 9 Old 05-25-2013
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Re: Diameter of Diesel Water Exhaust Pipe

Hello,

I'm confused. Is your engine fresh water cooled (has coolant) or raw / sea water cooled? If it is raw water cooled I don't know if it will get got enough to heat the water tank. Also, if your boat is in salt water i don't believe the water heater is designed for salt water.

If the engine is fresh water cooled then the water heater gets connected to the engine coolant, not the sea water / raw water pump. The connection should be:
engine block water OUTPUT to water heater input, water heater output to engine heat exchanger input, engine heat exchanger output to engine block input.

Good luck,
Barry


Quote:
Originally Posted by vtsailguy View Post
Wonder if someone can help me here....

I am connecting up a hot water heater. The current tubing from the diesel for the water exhaust is 3/4". I have a bunch of 1/2" tube lying around to run to the heater's exchanger.

Does it matter to the engine to step down to a smaller size tube, or is it important to keep to the 3/4" (i.e. have to by more tubing).

Barry Lenoble
Deep Blue C, 2002 C&C 110
Mt. Sinai, NY

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post #5 of 9 Old 05-26-2013
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Re: Diameter of Diesel Water Exhaust Pipe

What's the connection size at the heater? That's the size I'd use, and only make it smaller to connect at the engine. For freshwater cooled (i.e., heat exchanger) engines, the take off for the heaters is usually at/below the thermostat and back to the freshwater coolant pump, and NOT on one of the lines to the HX.

Stu Jackson, C34, 1986, M25 engine, Rocna 10 (22#)
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post #6 of 9 Old 05-26-2013 Thread Starter
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Re: Diameter of Diesel Water Exhaust Pipe

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Originally Posted by BarryL View Post
I'm confused.
Me too

Thanks to all these posts guys, it wasn't occurring to me that the hose I was seeing IS the closed loop for coolent. It's not raw water cooled.

So it sounds like I can just tap into that loop and run to the exchanger on the water heater., with no real issue with 1/2".....


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post #7 of 9 Old 05-26-2013
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Re: Diameter of Diesel Water Exhaust Pipe

As Stu indicated there's a 'standard' tie-in point for HW heater circuits. It would be wise to find out manufacturer's recommendations - you want the loop to be 'driven' not flow neutral.

Ron

1984 Fast/Nicholson 345 "FastForward"

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Re: Diameter of Diesel Water Exhaust Pipe

What engine do you have? Might help us to help you.

Stu Jackson, C34, 1986, M25 engine, Rocna 10 (22#)
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post #9 of 9 Old 05-27-2013 Thread Starter
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Re: Diameter of Diesel Water Exhaust Pipe



Volvo Penta MD2030 29hp


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