Water Heater replacement

Oct 1, 2008
148
Bavaria 36 Cruiser Nanaimo, BC
My old water heater (actually the fittings entering the tank) have given up the ghost. Due to the age of the tank (16 years old and it is aluminum), I am going to replace the unit and the external fittings. The old tank, and it's replacement (for ease of Hopefully plug and play) are Kuuma 11 gal. rectangular shaped tanks. These tanks have internal 1/2 inch NPT threads for the hot and cold water lines. On my old tank, there were metal "double male" fittings used at the tank (silver coloured) , followed by brass? one way valves, elbows, etc. The double males have rotted away (surprise) where they contacted the other (brass?) fittings. What material should I use for these "double male" fittings on the new install (aluminum, SS, or plastic) remembering that the internal tank is aluminum? The fresh water lines on this boat are Pex.
Also, the heat exchanger lines are attached to the new tank with a hose barb type fitting using hose clamps (appears to be room for only one clamp). Do I need to install any other fittings in the lines (such as one way valves, shutoff valves, etc.)? There is some kind of fitting in the old set up, but the attachment method is different (threaded and it could just be an adapter).
Thanks for the advise,
Tom
 
Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA
Tom.
Can you give us some pictures? Would help us to help you in identifying and resolving the problem.
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
Do I need to install any other fittings in the lines (such as one way valves, shutoff valves, etc.)?
At the cold water intake a check valve is often used. This prevents the HW from expanding back into the cold water lines as the tank heats up.

At the HW outlet a tempering valve is a good idea, this valve mixes cold water with hot water to maintain a constant temperature. It helps to prevent scalding from very hot water and conserves hot water. When the tank is heated while motoring, the water temperature will be roughly equal to the operating temperature of the engine, 180 degrees or there about.

If you winterize the water system adding a by pass and a drain will make the job easier.
 
Feb 6, 1998
11,667
Canadian Sailcraft 36T Casco Bay, ME
"Double Male" fittings are called "nipples"... Because a marine water heater is heated by an engine and can get to 180F or more I prefer to use brass fittings close to the tank. Once beyond the tempering valve and check valve you can convert to PEX. I will often use short SS braided hoses for supply and return line connections, to deal with vibration and then a simple 2" nipple can be used for winter by-pass.
 
Oct 1, 2008
148
Bavaria 36 Cruiser Nanaimo, BC
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Thanks for replying John,
I will try to attach a photo of the partly disassembled old water heater showing the engine loop plumbing and the metal "double male" near the top of the heater. Both "double male" nipples corroded and basically "fell apart" where they connected to the brass check valve or elbow, I am guessing from dissimilar metal corrosion. I will also attach a photo of the new tank.
Thanks,
Tom
 
Oct 1, 2008
148
Bavaria 36 Cruiser Nanaimo, BC
Dave (and all),
I am planning on installing a "heater bypass" for winterizing. Maine, I am most interested in feedback re: issues using dissimilar metals. On my old unit, the "aluminum looking" threaded nipple connectors (visible in the photo) had more or less rotten out and these joints fell apart when I was trying to unscrew them. Therefore, I was hesitant to use brass nipples directly into the aluminum tank for fear of a dissimilar metal corrosion problem?
The items already removed in the photo were on the cold water line: (connected to the aluminum (looking) threaded nipple) a brass one way check valve, a brass 2 way T valve for bypassing, and a brass adapter for changing thread size (listed from the tank outward). On the hot water line: (connected to the aluminum (looking) threaded nipple) a brass 90 degree elbow, a brass one way check valve, and a plastic T for the bypass (listed from the tank outward). The pex plumbing connects to the listed fittings and can be seen in the photo.
I am also wondering about the desirability of installing any fittings in the heat exchanger lines coming from the engine, such as shutoffs, etc.??
Thanks,
Tom
 
Feb 6, 1998
11,667
Canadian Sailcraft 36T Casco Bay, ME
Both "double male" nipples corroded and basically "fell apart" where they connected to the brass check valve or elbow, I am guessing from dissimilar metal corrosion. I will also attach a photo of the new tank.
Thanks,
Tom
It's possible someone used "dielectric nipples" for a land based water heater which are made from galvanized steel with a plastic insert. With aluminum tanks there will always be a risk of corrosion, heck we use aluminum as anodes, but they are cheap to buy on the front end. They just don't last as long as a full SS tank or even glass lined steel tanks, which I am also not a huge fan of.

If you look at your brass nipples for the engine HX, & the old T&P valve, you can see they've lasted 11 years with no visible corrosion... Course 11 years is not very long for a marine water heater..

Pay close attention to the factory installed T&P valve, brass into aluminum..... The plastic boiler drain is just a pathetic cost cutting method, I would suggest replacing it with a quality made brass quarter turn boiler drain drain.
 

bletso

.
Aug 20, 2013
106
Globe 38 PCB
"Double Male" fittings are called "nipples"... Because a marine water heater is heated by an engine and can get to 180F or more I prefer to use brass fittings close to the tank. Once beyond the tempering valve and check valve you can convert to PEX. I will often use short SS braided hoses for supply and return line connections, to deal with vibration and then a simple 2" nipple can be used for winter by-pass.
I like the idea of SS braid. I don't like what I did as Pex straight from WH is a bit stiff.
IMG_0537.JPG
 
Feb 6, 1998
11,667
Canadian Sailcraft 36T Casco Bay, ME
That's why I stop about 12" shy with the PEX and convert to flexible SS. For bypassing the tank in winter you simply unscrew the flexible hoses and put them together with a 2" nipple...
 
Aug 13, 2012
533
Catalina 270 Ottawa
A couple of questions:
- could you point me to a suitable thermostatic valve?
- does it need to be installed right on the heater? or can it be some distance away (I have really restricted space there). I imagine that this should not be an issue, especially, since i don't have a tempering valve in the first place.
- I have a valve in the coolant supply hose just before the W/H. Can it be left closed when the engine is running or is that loop critical for the engine cooling. Engine is Perkins M20. I think that it is just a side path and the coolant is diverted to heat the water. But I wonder if I am correct.
 
Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA
@dziedzicmj It is possible that you are correct, but there is no way for us to give you an educated/informed guess. You need to examine the whole length of hose. A previous owner/dock worker may have altered the hose lines. The factory may have changed the install.

Be sure that the valve does not shut off the coolant to the engine.


What may be happening... and I am just guessing because I have not inspected your boat... is the valve serves as a cut-off should you need to change the water heater, or winterize the water heater. Shut the valve and you do not have to drain the coolant from the engine. But I stress this is just a guess.

If the coolant flows from the engine in only one hose then shutting the valve will stop the coolant from circulating through the WH then onto the heat exchanger then back to the Perkins coolant tank. :yikes: You would put your engine at risk of over heating if the valve is closed and that is the flow plan (most likely in my experience).

Do the inspection and let us know what you find before you close a valve.
 

MitchM

.
Jan 20, 2005
1,011
Nauticat 321 pilothouse 32 Erie PA
what a beautiful job, maine sail. wish I saw that picture of yours before i replaced my isotemp HWH last year. (without the stainless lines that can screw together for a by pass ...)