Rheem Marathon Water Heater

[Skag]

My existing residential duty 30-gallon water heater just failed. I've been overwhelmed with the available replacement options and opinions as I surf the web and this forum....

My proposed solution is another residential duty unit that appears to be very well thought out and should never fail. It is a Rheem Marathon 20 gal water heater with a 120V 2KW heater. Has anyone else used one of these? Tank and outer shell are non-metallic and have a lifetime warranty. Thick foam insulation should keep the water hot for days. Not cheap, but neither are the "marine" water heaters that likely wouldn't last nearly as long.

For heating while cruising, I plan to put in an external exchanger (double wall plate type) mounted to create a thermosiphon using the drain and the relief valve connection.

 

[O C Diver]

Non metal water heaters have been around for about 30 years. They were originally designed for areas where water conditions would quickly eat the anode and then the tank liner. There high cost tended to limit their market ability inspite of them lasting several times as long as a normal water heater.

Don't know if the one you're considering requires a check valve to prevent the lining from being pull away from the insulation in vacuum. Basically the original design was designed to withstand the internal water pressure. When the heater was drained, there was the potential to create a vacuum in the tank which could pull the liner away from the insulation which provided the pressure resistant structure. If a check valve is required to vent the tank to outside air to eliminate the vacuum, I'm sure it would be covered in the installation instructions.

Ted

 

[Datenight]

My proposed solution is another residential duty unit that appears to be very well thought out and should never fail. It is a Rheem Marathon 20 gal water heater with a 120V 2KW heater. Has anyone else used one of these? Tank and outer shell are non-metallic and have a lifetime warranty. Thick foam insulation should keep the water hot for days. Not cheap, but neither are the "marine" water heaters that likely wouldn't last nearly as long.

For heating while cruising, I plan to put in an external exchanger (double wall plate type) mounted to create a thermosiphon using the drain and the relief valve connection.

I like this idea! If you go through with it I would love to see how you plumb the heat exchanger. I imagine the relief valve would be remotely mounted?

Following...

Rob

 

[jgwinks]

For heating while cruising, I plan to put in an external exchanger (double wall plate type) mounted to create a thermosiphon using the drain and the relief valve connection.

Be careful with the relief valve. If you use that conection put a tee in it to retain the valve. A slight overheat of the engine could build enough pressure to blow up the tank. It wouldn't have to be above 212 deg for very long. The old Mythbusters show did a couple episodes where they bypassed the relieve valves and thermostats on water heaters, they resulted in some of the most spectacular explosions they ever did. At about 200 psi the heaters exploded and took off like rockets. Of course they were set up for maximum drama, but they did demonstrate the danger.
While using waste engine heat is efficient and convenient, it can bring the water up way beyond the recommended temp for domestic hot water (120 deg?) a serious burn hazard. A tempering valve is recommended. Some marine heaters have tempering valves built in for that reason.

I have a residential heater in my boat too, I'm watching to see how you do that. It would be nice to not have to run the generator just to heat water.

 

[Pete Meisinger]

Go for it!

pete

 

[twistedtree]

Go for it!

pete

I like the idea. I think people typically stay with "marine" units because they typically have a lower profile and include a heat exchanger loop for engine heat. If you can work around those issues, it sounds like a good idea. Definitely keep us posted on how it goes, especially how you do the engine heat.

 

[Portage_Bay]

For heating while cruising, I plan to put in an external exchanger (double wall plate type) mounted to create a thermosiphon using the drain and the relief valve connection.

I haven't had much luck with thermosiphons. The work but can be very slow to get the job done. A low volume pump will help speed the heating process. You'll be running your main engine(s) anyway so the electrical load won't matter.

 

[Lepke]

You need to insulate the lines going to and from the water heater for at least 6' so they don't draw heat out. I have a 50 gallon house water heater sitting on 2" foam and 2" foam all around including the top. Hot lines are insulated and incoming cold for 6'. It retains heat for several days depending on use. MY diesel stove has a water coil that keeps it hot in mild weather.

 

[Turtle Blues]

Have installed several in residential high iron / hard water situations. Desire was the lifetime warranty on the tank knowing that replacement of the standard heater elements was going to be necessary every couple of years. As others have said the proper venting and valving in your piping system in the important issue.

 

[Skag]

Thanks for the reply guys. Some good advice given. Thank you. I placed the order and hope it comes soon as I am living aboard and currently have no hot water......

The advice to keep from pulling a vacuum makes sense. I do plan to maintain the relief valve (might be dual purpose vacuum and pressure) that comes with the tank. If I can't find a suitable low pressure drop exchanger that makes a thermosiphon easy to do, I will go with a 12V pump - as someone wisely stated my 12VDC usage will not matter when using the engine to heat. My current residential heater does not have engine coolant hoses running to it. I'll have to do some research on how to properly hook up to my 3306 Caterpillar.

I will post when I make progress.

Regards,
Craig

 

[Simi 60]

We cruise full time, no marinas 2 on board.
We recently got rid of the power sucking 1.8kw Rheem HWS and replaced it with a 2 4 kw Rheem.
This one was only 25 litres/6 gal.
I leave it on full time, no need to worry about power, it just does it's thing.

One of the best things we have done in 6+ years out here.
Instead of taking hours sucking the batteries/solar/Genset dry it only takes 15 minutes.

And we get a massive amount of extra storage space back
One day I'll think of something to put there.

 

[timb7734]

Sounds too big and heavy, not knowing your boat or cruising style, unless you need/want to sit in cold, remote anchorages for days on end the size of this heater would seem to be a big space/weight compromise. I get by with a 6 of 8 gallon and a brief gen run daily.

 

[Skag]

Thanks timb. Boat is a very heavy (105,000 lbs) 50’ steel trawler. Prior hot water heater was even larger (30 gal). I liveaboard so don’t want to compromise my shower time. Rheem I believe had a smaller one (15 gal?), but the 20 fits perfectly in the space my 30 gal occupied. I hope to not have to run the engine or gen for days when anchored out. The insulation on the Rheem marathon is impressive and the non-metallic tank should outlast me.

 

[Skag]

Well..... 1 month later and I've returned the 20 gallon water heater and purchased the slightly smaller 15 gallon water heater. The 20 was perfect for the space, but I failed to measure the stairway down to the stateroom where it was to be installed. Missed it by 1". I know better.... measure twice, cut once........ I felt like a complete idiot. Had a few beers and moved on. Will post when I'm done. I am still impressed with thermal insulation of these marathon non-metallic water heaters. The pic is of the "smaller" 15 gallon which cleared my stairwell by 1/2" - at 15 gallon it is still a beast at 21 3/4" dia and 35 3/4" high.