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Old 02-13-2014, 07:34 AM   #21
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They do sell home type water heaters with heat exchanges for homes with solar systems....

but I think you will find the sizes and prices to not be advantageous.
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Old 02-13-2014, 08:37 AM   #22
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If I had 24 years of service with a marine water heater, I think I would replace it with the same make and model. Most likely, you won't still have the boat 24 years from now so let someone else worry about it. Also, replacing the heater with the same make and model is far simpler than rerouting or extending water and electric lines.

I think it would be a big mistake to use a non-marine water heater on a gasoline powered boat and it would be a big mistake to use a water heater without the heat echanger feature if you plan to anchor out or use hot water underway without running a genset.

After a day's travel, I still have hot water the next morning because of the heat exchanger in my water heater.
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Old 02-13-2014, 08:46 AM   #23
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The Atwood website says their marine units are ignition protected. The instruction manual says to "locate the switch in an area where ignition protection is not required."

Ours is installed in the engine room (diesel boat), and the controlling breaker is on the AC/DC distribution panel in the saloon. There is no other "switch" on the unit, so I'm guessing (hoping) this installation suffices.

I know the boat manufacturer moved the unit out of the engine room in later models, but was told that was at least partly for space concerns, so they could also install a slightly larger generator (ours is just adjacent to the HWH).

I'm satisfied enough with our unit, but if I were replacing and wanted to use an Atwood model, I think I'd have a conversation with them about that "switch vs. ignition protection" thing anyway, just to understand better what they think they mean.

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Old 02-13-2014, 09:01 AM   #24
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Ignition protection is as simple as a screen...like on alternators or back-fire flame arrestor on carbs..nothing magical...

Not sure what would be required to "ignition safe" a water heater but it wouldn't be much I'm sure....but I know the "sea lawyers" will wince at the suggestion and worry about voiding their insurance.

The OP has a 44 Sea Ray...can't be sure but it may be a diesel anyway.
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Old 02-13-2014, 02:49 PM   #25
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I have a 11 gallon Attwood that is 27 years old the only part I've had to replace is the safety pop off valve, if I ever have to replace it the same thing will go back in.
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Old 02-13-2014, 02:56 PM   #26
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You wouldn't
Easily done and inexpensive as well:

B3 12A 10 Plate Heat Exchanger 7 5" x 2 9" w Studs Stainless Steel Copper Brazed | eBay
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Old 02-13-2014, 03:01 PM   #27
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And that is going to heat the tank how? Add a circ pump, design a thermal siphon??
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Old 02-13-2014, 03:36 PM   #28
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That'll work. Or just put it on the cold water inlet
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Old 02-13-2014, 05:52 PM   #29
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Seaward Aluminum Tank

This tank was 13 years old when it failed. Seaward sold me a replacement tank and suggested I include a anode which would in their opinion prevented this rupture. They were prompt and friendly.

I currently have glass lined residential 20 gal which provides me with hot water at least 24 hrs without power. I run the generator to recharge my battery bank first thing in the morning. Cooking is electric as well as heat, or cooling so we try to time power usage while charging the batteries. Plenty of hot water for showers or laundry if needed. I haven't missed using engine coolant to make hot water. Or for that mater the scalding from super heated hot water. The engines do run at about 180 deg.
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Old 02-14-2014, 05:47 AM   #30
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One concept to avoiding a ruptured tank might be to use a FW pump that has much lower pressure.
And cycle the overpressure valve on the heater tank more often.

Might make the dishwasher or washing machine unhappy but normal living should never notice.

The larger the supply tubing , the easier it is to live with 20 - 30 PSI instead if 55psi.

Be sure to use a rebuildable and adjustable pressure regulator if you run dock side water aboard to the boats FW system.
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Old 02-14-2014, 08:05 AM   #31
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Ignition protection in an electric water heater would be the thermostat. The thermostat would have to be designed to be ignition protected i.e. designed either to not produce a spark or to isolate any spark from potentially explosive vapors.

When thinking of things like ignition protection, I am not concerned with insurance (which would be in force regardless), but with the safety of myself and my family.

Not too long ago, a boat exploded and burned just after being launched at a local boat ramp. Fortunately, the people were able to get off without injury but it could have ended differently if they had been away from land.
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Old 02-14-2014, 09:24 AM   #32
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The unit you refer to is finned, therefore designed to dissipate heat, not collect it and is most likely too small, the same mfg. does have a $250 exchanger but by the time you build a heat trap box around it and add a pump or engineer and build a heat siphon ... well, like I said... you don't.
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Old 02-14-2014, 09:36 AM   #33
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Ignition protection in an electric water heater would be the thermostat. The thermostat would have to be designed to be ignition protected i.e. designed either to not produce a spark or to isolate any spark from potentially explosive vapors.

When thinking of things like ignition protection, I am not concerned with insurance (which would be in force regardless), but with the safety of myself and my family.

Not too long ago, a boat exploded and burned just after being launched at a local boat ramp. Fortunately, the people were able to get off without injury but it could have ended differently if they had been away from land.
Ignition Protection



ABYC Definition of Ignition Protection




E11.4.15 Ignition protection - the design and construction of a device such that under design operating conditions:

a. it will not ignite a flammable hydrocarbon mixture surrounding the device when an ignition source causes an internal explosion, or

b. it is incapable of relasing sufficient electrical or thermal energy to ignite a hydrocarbon mixture, or

c. the source of ignition is hermetically sealed


What this means
If gasoline vapour is present in a space all of the electrical equipment in the space must be ignition protected to avoid causing a fire. Unless specifically labelled "Ignition Protected" all electical equipment is assumed to be capable of causing small sparks which can start a fire. Even fuses can cause a fire when they blow unless they are specifically designated as ignition protected fuses. The standard also applies to spaces with CNG or propane in specified concentrations. Ignition protected equipment is specially designed to prevent sparks either because the electrical connections are in a hermetically sealed container or because they have been designed to prevent heat transfer to the atmosphere.

Which is nothing more than a metal screen as in a backfire flame arrestor....the engine still backfires but the flame front is dissipated by the screen...as are the screens on many alternators...

How does a Flame Arrestor Work? - Ask.com

How does a Flame Arrestor Work?


Answer

Flame arrestors work by providing enough surface area to extract energy from the front of flame to extinguish it before it exits flame arrestor.




2 Additional Answers


A flame arrester functions by forcing a flame front through channels too narrow to permit the continuance of the flame. Flame arresters are used to stop the spread of an open fire, to protect explosive mixtures from igniting, and to confine fire within an enclosed, controlled, or regulated location.



A mechanical flame arrestor is filled with metal or ceramic and this absorbs heat from a flashback, quenching it to a temperature below what is needed for ignition.
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Old 02-14-2014, 06:01 PM   #34
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The unit you refer to is finned, therefore designed to dissipate heat, not collect it and is most likely too small, the same mfg. does have a $250 exchanger but by the time you build a heat trap box around it and add a pump or engineer and build a heat siphon ... well, like I said... you don't.
Would someone care to explain a plate heat exchanger to a surveyor?
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Old 02-14-2014, 06:42 PM   #35
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One concept to avoiding a ruptured tank might be to use a FW pump that has much lower pressure.
And cycle the overpressure valve on the heater tank more often.

Might make the dishwasher or washing machine unhappy but normal living should never notice.

The larger the supply tubing , the easier it is to live with 20 - 30 PSI instead if 55psi.

Be sure to use a rebuildable and adjustable pressure regulator if you run dock side water aboard to the boats FW system.
I don't think the water pump was the culprit, The pressure might of come from high pressure from the hot water and pressure relieve valve failing, however it worked. The crack in the tank was well oxidized leading me to think the aluminum had weakened due to the welding of the tank. At any rate Seaward didn't sound surprised and suggested the adding a an anode.
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Old 02-14-2014, 09:32 PM   #36
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The unit you refer to is finned, therefore designed to dissipate heat, not collect it and is most likely too small, the same mfg. does have a $250 exchanger but by the time you build a heat trap box around it and add a pump or engineer and build a heat siphon ... well, like I said... you don't.
That's a plate heat exchanger and is a similar size as the Alfa Laval I have sitting in my shed as a someday boat project. I was going to use it for hydronic heating, but it would work well for hot water too. I like the idea of having a closed circuit on my coolant line as it supplies the turbo jacket.
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Old 02-14-2014, 09:39 PM   #37
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That's a plate heat exchanger and is a similar size as the Alfa Laval I have sitting in my shed as a someday boat project. I was going to use it for hydronic heating, but it would work well for hot water too. I like the idea of having a closed circuit on my coolant line as it supplies the turbo jacket.
I bought one similar to what Rick linked...maybe a higher BTU exchange/better quality (I hope) as it was a bit more expensive.

I was nervous about adding a bus heater along with the existing hot water heater so I looped the two of them and now the engine coolant loop is only 2 feet instead of 20+..makes me feel a bit better but I'm not sure that's the application Rick was posting for...

I'd have to think a bit longer on uhow I would use it on a hot water heater without an internal exchanger...sure I can think of a couple ways...just wonder what would work best.

Take a look at these pumps for when you get around to it...mine works pretty well...$50 or so...

Solar Hot Water Pump Run on 12V Battery or Solar Panel Good to 230į F 145PSI | eBay
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Old 02-15-2014, 06:34 AM   #38
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On most >marine < hot water heaters you can not use a box heater in series with the FW unit.

Many FW heaters attempt to limit the temperature in the water by shutting down the coolant flow.....Much Ungood with an inline heater.

Two parallel circuits is required , an added high volume pump may be required for the box heater as many are 40,000 btu to 120,000btu and need Lots of supply to function .Usually a centrifugal ,as with engine power 10A to move the water is no problem.
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Old 02-15-2014, 08:13 AM   #39
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On most >marine < hot water heaters you can not use a box heater in series with the FW unit.

Many FW heaters attempt to limit the temperature in the water by shutting down the coolant flow.....Much Ungood with an inline heater.

Two parallel circuits is required , an added high volume pump may be required for the box heater as many are 40,000 btu to 120,000btu and need Lots of supply to function .Usually a centrifugal ,as with engine power 10A to move the water is no problem.
Geez, I am shaking my head ...

"Shutting down coolant flow" ... look at the water heater connections on your engine. I believe 99% of you will see that that water is tapped off in a manner which has zero effect on the engine. How do you think a cab heater works in a vehicle which uses the same engine? Your engine probably has shutoff valves in that loop anyway. Are they part of a self-destruct system? I think not.

The link to the plate heat exchangers shows multiple sizes and ratings.

Installing a plate heater on the engine coolant loop is a no brainer. If you already have connections for a water heating loop, it simply replaces that one. A thermosyphon requires nothing more than a connection to the w/h drain fitting to supply cool water to the hx inlet, and a connection at the hot outlet at the top of the tank for the warm water from the outlet

A temperature limiting or blending valve on the heater outlet ensures there are no issues with boiling water. Your hot water system should have one in any event, it is a safety item.

It doesn't get much more simple and foolproof.
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Old 02-15-2014, 08:47 AM   #40
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Would someone care to explain a plate heat exchanger to a surveyor?
The referenced heat exchanger is identical to one on my vessel used for the hydronic heating system. These types of exchangers are and have been used in all sorts of applications for a very long time and conceptually identical to steam radiators used to heat buildings and homes for pushing two centuries,

The heat exchanger is about the size of two packs of cigarettes. It is attached on the engine side "heater" hoses and provides boat heat when cruising with diesel fired boiler off but the hydronic loop pump on..

Interestingly, when at the dock or at anchor and the diesel boiler operating to provide boat boat heat, it will passively heat the shutdown engine quite nicely provided the "heater" valves are open. It could heat a hot water tank the same way, either with the boiler operating or the engine running.

My Torrid hot water tank has the internal engine loop heat exchanger so on that engine I have no need for the plate heat exchanger.
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