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Old 17-09-2014, 09:48   #1
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Water Heater Plumbing

About to install a Kuuma 6 gal water heater. The instructions have a schematic showing a bypass hose and valve teed into the engine coolant in and out lines outside of the heater. No explanation on the reason for the bypass. I have never seen this on a heater and the old Raritan didn't have one.

Presumably, opening the bypass valve all the way would reduce coolant flow to the heater by half, and closing it would send 100% flow to the heater. Is this really necessary? If it's a way to regulate temperature it is pretty clunky and inconvenient.

I'm tempted to skip the bypass and just plumb direct in and out lines. Does anyone know if this would cause a problem? The engine is a Universal M25 and the pressure water lines are pex type plastic. Thanks in advance for any suggestions!

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Old 17-09-2014, 09:55   #2
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Re: Water Heater Plumbing

Mine has a bypass, but its to mix the heated and none heated fresh water to prevent scalding. The engine will heat the water way to hot for use.

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Old 17-09-2014, 16:33   #3
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Re: Water Heater Plumbing

May be to bypass the WH all together. The valves direct water flow either thru the WH or thru the bypass valve, not for a combining usage.

This is so when you winterize, you drain the WH and all lines, then position both valves to 'remove' the WH from your plumbing system. Then when you add RV/Marine antifreeze to run thru your plumbing you won't be filling the water heater with AF.
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Old 17-09-2014, 16:40   #4
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Re: Water Heater Plumbing

I would do it the way they recommend. It could be that the flow restriction of the hot loop is too high and the bypass is to reduce that restriction. The temperature will not be affected much by the bypass. Only the time it takes to heat the tank will be affected. If you have a fresh water cooled engine the heater water will reach the engine water temp eventually no matter what you do. And yes, for most diesel engines that means it will get too hot so be careful when using hot water from the tap.
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Old 17-09-2014, 17:21   #5
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Re: Water Heater Plumbing

For an M25 engine, just plumb it straight. The bypass is usually for "separate" winterizing, do it if you feel you need to, it saves a lot of work every year.
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Old 18-09-2014, 04:34   #6
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Re: Water Heater Plumbing

Never seen one plumbed with a bypass on the jacket water line. I wonder if that's only if you actually cut into an existing hose to extend it to the water heater loop. Then you'd want to make sure that loop didn't present a restriction in flow. But every one I've seen adds a NEW loop from, and back to, unused fittings in the engine coolant system. Or, worst case, a "T" fitting. That way even if the water heater loop is 100% blocked, it doesn't affect the normal flow of coolant in the engine.

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