On-Demand Hot Water Heaters

O

Overextended

Member
Feb 13, 2007
307
chesapeake
Boat Info
36
Engines
cummins
Does anyone have any experience with the few electrical powered on-demand hot water heaters that are sold for boats (like the eemax tankless water heater)?

Looks like they run about $400, they appear easy to install, the question is do they work.

On the 36 Sedan there is a 6 gallon hot water heater; same as our old 320. On our old 320 all three of us could take a shower and still have hot water, on this boat my wife barely got done before it got cold. So either the flow rate on the shower head that they installed is too high vs the old one in the 320, or maybe the hotwater heater isn't heating the water hot enough for a lower mix of hot vs cold water which would extend the time available in the shower. Shower ran for four minutes before there was no hot water left on the boat.

Right now the dealer/Sea Ray is looking into whether the hot water heater is doing what it should, but I guess I might be interested in adding something that could potentially give us unlimited hot water...again if they work.

Any experience here?
 
Check the power demands. They draw two to three times the power.
 
I can't imagine your current hot water heater is working correctly. There are 6 of us on our boat and everyone takes a shower in the morning (2 showers running) and we have never run out of hot water... plus my boys like to stay in the shower way too long but we won't go there... I'm not sure how the heater keeps up but it must have the ability to almost heat the water on demand as it is. I would assume your boat has a similar or better system that my old archaic boat.
 
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The way instantaneous water heaters work is decreased flow rate + increased wattage. Better check the current draw from the manufacturer if you plan on using it with your generator, especially if other loads like the AC are on.
 
I'd replace the 6 with a 10 gallon unit. The advantage to the tank units is their ability to use engine coolant to heat the water. Hottest shower in you life is the one you take just after a trip. With a tank one you'd have to run the genset or use shore power. If you're on shore power then the marina's bath house would have lots of hot water. I've not seen any setups looping the genset coolant through the hot water heater so it just ends up being even more wasted fuel.
 
gary,
We run out of hot water all the time. ( two girls ) The instant hot water draws 20 amps.... rated on certain temp rise.... soit will only raise the water temp a set amount. ( i think is 30 or 40 degrees ) based on what i read in worst marine catalog. I also was looking for more hot water....

Rob
 
I would agree with Gary. It doesn't sound like the heater is performing as it should. If your damand for hot water is higher than others I would also look in to option suggested by wkearney99. I'm not familiar with tankless units on boats, but my friend did intensive research on them for his house and the reality shows that it more of an illusion than something that really works. There were cases when new communities were built with these units. A short while later all of them had to be replaced in every house due to major complaints from owners.

So for the house I'd say forget it. For the boat I would still think twice. Since we know one technology that works fine, why change it. Just get a unit that would be large enough.

Hope this helps.
Alex.
 
I don't know... maybe the 480 DB has a bigger tank... I know I've not run out and I'm usually the last guy in every morning.
 
You can turn the water heater thermostat up to a much higher setting. When mixed with cold water, it will last longer. The downside is that the hot water might be too hot. You can use a thermostatic mixing valve on the heater's output to bring the temp from 180 or so to 120, which is safer.

Best regards,
Frank C
 
Great feedback all. First I am going to try to up the preset temp on the current hot water heater, but it is currently working and making hot water.

Gary - it is only a 6 gallon, on your boat you have a much larger one...the 36 Sedan is the only Sport Yacht that they used a 6 gallon in, the other Sport Yachts per customer service get a bigger heater, Yachts get an even larger unit.

WKearny - My hot water heater is not hooked up for engine heating, just AC.

Rob - My hot and cold distribution mainfold for the boats systems is under my galley steps where the beam vacuum is located (I could splice into that and get the correct power 20Amps -- as long as I turned the hot water heater off before using the vacuum.

Rob and all - I think the problem is that they put a shower head with a really high flow rate (water comes screaming out of there) on a boat with a water heater that should be back on my old Sport Boat. With the high flow it tears through the hot water - I have been down to the boat at our dock and turned the water to a good shower temp and timed 4 - 5 minutes of run time before it poops out (that will never cut it). I am contemplating adding the on-demand heater in the compartment where the manifold is (power from Beam circuit - just make sure to switch off the hot water heater before using the beam). I am thinking of running the cold water shower line through the on-demand heater to get a rise in temp of 17 degrees on the cold side. When the warm water coming from the cold side is mixed with the HOT water from the hot side my thought is that I will use much less hot water in the mix and seriously prolong the flow of hot water in just the shower compartment.

Any thoughts on this idea??
 
On the 320DA the HWH to shower is a short run, so part of the problem is the longer the run the more heat you loose through the walls of the plastic tubing.

I have an 11 gal HWH on the 48DA and we run out also, and there are only 2 of us. (never ran out on the 390DA though, go figure) What I found was to turn on the fresh water pump and mix in your on board tank water with the city water from the marina. As the weather gets better, the tank water is warmer then the city water provided by the marina and the hot/cold mix alows you to dial down the hot and still get a great shower. The pump combined with the city water also boosts the pressure at the shower head, so you can also reduce the time you take to wash up.
 
This has been a bit of a mystery to me as well. We moved up this season and went from an 8 gal HWH on the 44 Sundancer to an 11 gal HWH on the 48. Grohe hardware on both boats and the same use habits (we don't let it run continuously) by the two of us. We never ran out of hot water in the shower on the 44 and now always do on the 48! While I haven't measured it, the 48's hot water seems to be much hotter.
 
Guys, Not to change the subject but those 48DA'S are really nice looking boats!!!!!!!!! JC
 
Stan
Come to think of it you're right, the water is hotter on the 48 then I remember on the 390. With that you would think adding more cold to get it right would increase the time it lasted but it just doesn't. I'm the first one up and I can't start the day without a shower so it's first come.....sort of survival of the fastest! lol

JC3 thanks I'm sure from both of us.

I think there are a few more 48DA's on the board. Me, Stan, Missnmountains, and Daniel that I know of, so lets get started on a thread and lets compare options and what works and doesn't.

Rich.
 
OVerextended.
IT should work well.... as long as u follow ur shut off sequence.... I cant get anyone to shut anything off .... we blow breakers all day long....

Back to the shower for a sec... in the am... Wife and i take military showers ... which i hate and still run out of hot water... The thermostat on my heater is fixed. ITs a thermodisk... no adjustment.

Rob
 
OVerextended....
I have the 36 Sedan Bridge, and showers have never been a problem. We have had four back to back showers taken (two women that take long showers as well), and have never run out of hot water in last years 2007 36 sedan bridge, and this years 2008 sedan bridge. Seems like something is not right with the heater, or the faucet. Our faucet as well is high pressure...but stays hot. We did have the valves backwards last year where hot was cold, and cold was hot. I can't imagine that being the problem...but worth checking out.
 
Robski, mine is fixed also, but measured the water coming out right at the heater and it is only 120, manufacturer says should be 140 so a replacement thermostat is on the way. Check your temp also you may have same problem.
 
The thermostat is a fixed temp thermostat and the guys at Attwood said that if we were only getting 120 deg water vs the spec 140 then that would be the thing to replace first. Marine Max has one on order and I hope to have it in and tested before we leave the dock for the next week and a half this weekend. It should fix the problem, if not I might just pull it out and replace it with a 20/or do the on-demand heater on the cold side of the shower...will keep you posted once I get the replacement thermostat under warranty tomorrow..
 
Overextended said:
On the 36 Sedan there is a 6 gallon hot water heater; same as our old 320. On our old 320 all three of us could take a shower and still have hot water, on this boat my wife barely got done before it got cold. So either the flow rate on the shower head that they installed is too high vs the old one in the 320, or maybe the hotwater heater isn't heating the water hot enough for a lower mix of hot vs cold water which would extend the time available in the shower. Shower ran for four minutes before there was no hot water left on the boat.
?
Click to expand...

Don't know what you ever figured out about this, but I did own a boat once where the water heater had been replaced, and the lines were hooked up backwards. So, Coolant in the tank, and fresh water flowing around it. Needless to say, 2 minutes of hot water.
 
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