On Demand Water Heater

Here is a website that has several models available:

Precision Temp Boat Tankless Hot Water Heater. Gas Marine Water Heaters. Propane Boat Hot Water Heater

Electric or Propane? What size vessel? I retro fitted a 45 meter Benetti with two Titan Stainless steel electric commercial units 220v 3 phase for a hot water deck wash system and learned some valuable lessons. Going into the project I knew that we would have to upgrade the circuit protection and valving.

1. The amperage draw was 15 % more than the manufactures listed figures.

2. On demand hot water units don't function well with long circuit loops even with hot H2/0 circulator pumps involved.

3. After the breaker upgrades @ the switchboard and wire size upgrades (amp draw) at the end of the day it wasnt worth the $$ and effort as we should have just mounted a seperate boiler as we had the space for it but you might not

This being said, If your boat isnt that big and u focus on the electrical upgrade vs space savings it might be a (no pun intended) "a wash"!

Captholli
What!? Are you serious? My grandma could had told you those silly things while your BSing on these yachts....Ha JK!
I am hoping you might explain more why the on demand did not work well with the longer plumbing runs and circ pumps. I have heard countless times people considering on installing them on there boats and always did wonder if it was good idea or bad idea. I also never really knew what activates those units either, flow or psi switch? Something else?

They don't work well IMO. If the water is hard, which it is a lot of times in South Florida. They last less than a year, it zaps the minerals right onto the heating element and they stop working. They also don't maintain and even temperature, especially on a yacht unless you put a water pressure regulator right before them......and they draw a lot of amps when they come on.....Also, if you lose power or are on anchor without AC voltage, you lose hot water instantly......At least with a hot water tank, you can take a couple of showers with hot water......

To answer C4ENG questions about the why's

While the hot water is circulating through the insulated Loop around the vessel when you have flow from the on demand heater you have the problem of flow limiters in the ODH that restricts the output until it comes up to the desired set point. The smallest of these units seem to be around 2-3 Kw with flow rates of 2 gallons per minute and the units I installed were 27 kw with flow rates of around 5 to 6 gals per minute x 2
So we found that when two washdown hoses were going at the same time the hot water output from the ODH wouldnt keep up with demand and we would suffer drastic pressure loss due to the limiters trying to keep up. We defeated this issue by installing themostatic mixer valves down line from the
ODH to allow more water flow from the vessels boilers to make up the difference but in doing so we defeated the whole purpose of having stand alone ODH.
The units operate with flow sensors to activate the electronic power supplies
to energize the heating elements and that being said these electronic power supplies are big power consumers so when you spec a system out for lets say 15 Kw that figure only relates to the element Kw and not the entire system power supply and all.

captbg , I would really do some load calculating on one small unit before taking the plunge as its one thing to place a ODH in a house with a 100 amp service coming off the grid but its another type of animal on a boat. If your really set that you need two units for the flow rate that you desire than you might want too add a second 50 amp shore line and a larger Gen (lol) because these units are huge power hogs!!

Captholli
That was very interesting of what sounds like good theory in concept but is not what is true in real life, and you do not know until you know from experiences or from others sharing what they learned.
Thank you for not taking my off color grandma joke wrong as I promised myself that, while in the safety of my living room, I would not drink and YF, But only when I am in my cabin and in charge of millions of dollars of machinery.
Wait, was that off color again? Dag Nabit!

Just go to Lowe's website or Home Depots, and real ALL of the reviews.....many issues with them......the solenoids inside freeze a lot and they stop working, the water pressure has to be consistent, and a filtration system before them is critical........they're really not worth all of the trouble IMO, except maybe in a few rare cases.

On the other hand, while I don't believe they are practical for most boats, I have had one in my home for around 10 years and have had no problems with it.

It is made by this company: Tankless Water Heaters 1 800 Tankless 800 826 5537 MADE IN USA Residential Commercial hot water heaters