Hot Water Heater Recommendations Please

[michaeld]

I have spent quite some time Googling for a hot water heater. I'm confused, so I'm hoping collective knowledge/expertise will help point me in the right direction. Assume only two aboard, water conservative showers. Engine heat exchanger and 115VAC required. No more than 5-6 gallon size.

Experience & advice solicited... Make/Model Good/Bad/Ugly

Thanks!

[PippaB]

Out boat came with an Isotemp, I believe the "Spa" series (or its predecessor). Our is 5.5 gallons/25 liters. We have never run it on the electrical circuit, so can't comment on that side of things, but we do have it connected to the engine. Keeps water hot for 24-48 hours in the tropics, warm for another day. 24 hours only in more temperate climes. Easily enough water for two of us to shower without reaching the end of the tank.

With engine heat driving the water temperature to 75-80C the tempering valve is a must. Ours did stop working at 10-12 years old, simply replaced with a standard device from the plumbing store.

If I were installing from scratch I might consider one of the diesel-fired heaters designed for space heating, but we also frequently sail in areas where heat is more necessary than FL.

[rbk]

I’ve been looking as well and isotemp looks good but I’ve been seeing too many horror stories recently and they all seem to be similar stories. They really look like a quality product, good insulation, decent price and mixing valve (most don’t) but rusty failed welds keep popping up in reviews. If isotemp would acknowledge this and correct it I wouldn’t hesitate, until then I’m sceptical. While warranty does seem to be honoured it’s still the inconvenience of replacing seals, or swapping the tank, purging the cooling system etc every year or two.

[Nord Sal]

Why would you need to heat hot water?

[more]

Originally Posted by michaeld

I have spent quite some time Googling for a hot water heater. I'm confused, so I'm hoping collective knowledge/expertise will help point me in the right direction. Assume only two aboard, water conservative showers. Engine heat exchanger and 115VAC required. No more than 5-6 gallon size.

Experience & advice solicited... Make/Model Good/Bad/Ugly

Thanks!

https://www.svb24.com/en/quick-warm-...boiler-b3.html
USA shop
https://www.mauriprosailing.com/us/p...05S000A00.html

https://www.quickusastore.com/boat-s...-water-heater/

this is a working horse 20-30 year usually without problem

[dlj]

I have an Isotemp Slim B 25 liter. It came with the boat and runs very well. Has both heat from engine and electric when I have shore power. I can run it off my inverter but typically don't. Keeps water hot a long time, like a couple days.

dj

[Marathon1150]

I replaced a Raritan 10gal tank that was more than 30 years old and was still working fine, more or less. I replaced it on the advice of Raritan because they could not provide a new thermostat for the tank and in their view, it was time to retire it. Other than the thermostat, the tank had no other issues.

I replaced the above with a new Raritan that was the same physical size but only holds 6 gallons (US). Over the years, Raritan has added a lot of insulation to their tanks. The tank is under the V berth and during the colder months, provided a warm bed. The new tank doesn't leak enough heat to accomplish this desirable outcome but we aren't wasting power either.

Our second boat also has a Raritan tank that is now about 25 years old. Still going strong and no issues during the 3 years that we have owned this boat.

Both are connected to the engine cooling system and both are wired to the 120V panel when we are connected to shore power. I wouldn't hesitate to buy another Raritan despite the price.

[clongcor59]

We Installed an Isotemp Spa 20 (5.3 Gal.) 3 months ago. Very pleased so far. Takes about 1 hour to heat from cold to full temperature (on electric) and water stays hot a long time. The two of us have not yet run out of hot water.

I was not aware of any weld failure history with Isotemp. Guess I will find out first hand.

My opinion is the thermostatic mixing valve is a critical safety item that I would not go without. I have dialed the thermostat way down and the output is still dangerously hot with out it.

[rbk]

Originally Posted by clongcor59

We Installed an Isotemp Spa 20 (5.3 Gal.) 3 months ago. Very pleased so far. Takes about 1 hour to heat from cold to full temperature (on electric) and water stays hot a long time. The two of us have not yet run out of hot water.

I was not aware of any weld failure history with Isotemp. Guess I will find out first hand.

My opinion is the thermostatic mixing valve is a critical safety item that I would not go without. I have dialed the thermostat way down and the output is still dangerously hot with out it.

I really hope you don’t have any issues. I would love to hear that these are one off or limited issues. Love the mixing valve and the price. Would like to hear other positive outcomes from isotemp.

[malbert73]

I replaced my 32 year old Raritan as part of “while you’re at it” proactive refit in that part of the boat. So that’s a good endorsement. Also, it really holds heat for a while- over 24 hours later at anchor it’s still hot

[rslifkin]

The original Raritan water heater (12 gallon, no heat exchanger) on my boat made it about 19 years. The replacement (another of the same) is still working fine after another 17. I'm doing some major water system work this year, however, so I'm probably going to replace it. The outside of the tank under the insulation is a bit rusty, and it's just not all that well insulated. So I'm left with the choice of clean up and re-insulate an old water heater or buy a new one.



The replacement for my boat will almost definitely be an Isotemp Spa 40 with the upgraded 1200w heating element. It's got the best insulation out of the box from everything I can find, and I don't want a unit with an aluminum tank. Plus the Isotemp mounting is stronger than the Raritan mounting for the larger sizes, which is a big plus (the Raritan mounting without the optional upper brace has always seemed a bit weak to me).

[malbert73]

Originally Posted by Nord Sal

Why would you need to heat hot water?

Hot showers?

[steve77]

Originally Posted by malbert73

Hot showers?

He's referring to the seemingly redundant term "Hot Water Heater". Some people think it should just be a "Water Heater".

We installed an Isotemp Slimline about 4 years ago and have had absolutely no issues with it. Like others have said, it keeps hot water available for a long time and is easily adequate for two of us on board. We regularly use the unit powered by AC (genset or shore power) as well as from the auxiliary.

We are very happy with the Isotemp. Cheers!

Steve

[alaskanviking]

I have an isotherm 40L. It came with the boat, not sure when it was installed, guessing 15-20 years old

It has always worked well, water stays hot ~24 hours. The 750 watt electrode has generally heated water fast enough. Not sure about the quality of the newer ones.

I will be installing a new one later this year, redoing my water system. I need a dual heat exchanger model so I can heat both with the engine and with a diesel water heater. There is a isotherm 40l dual exchanger model ~$1200, US made stainless tank.

I have also been looking at some of the UK water heaters. Surejust, Surecal and Hotpot are 3 of the brand's. These have copper tanks, dual exchangers, and can choose different electrode elements including a dual 240vac 750w/ 12vdc element that would be easy to tie into your solar. The elements are Titanium which matches high end house hot water heaters in the US. the insulation is the waterproof poured foam type so it will be good even if it gets wet, similar to isotherm. Many US marine water heaters use regular fiberglass insulation and when it gets wet it degrades and won't hold heat.The copper in the tank is supposed to be antibacteria, and in theory will remove the dissimilar metals from your potable water supply if you use copper or plastic fittings. Heat exchangers are also copper so they will transfer heat from the engine more efficiently. The include a antiscald temp mixing valve which appears to only come on the higher end us units. I found these in 30-40l for approx $800 but you need to include shipping, so I've been estimating ~$1000

I have not been able to find a comparison between the UK heaters and us heaters. So it's all guestimate, however I seen canal boats review them well and they appear to hold heat for 24 hours. The copper as an antibacterial, well that is generally true and it makes sense that bacteria and scum doesn't grow on the inside of the tank. not sure if the application here works well for that. I have a 240v system, but they do have 120v electric heating elements, you will have to order it with it or order the extra element and install it yourself later. The dual ac/DC element only comes in 240v/12v however so if you only have 120v that may not work for you. The copper tank can have issues with pressure. The pressure valve is set low on the UK models 3-4 bar. If the water heats up and over pressurises, then cools and contracts repeatedly the copper work hardens and can crack. I'm not sure how or how often this will affect you in reality but something to look into and consider because you more than likely have to upgrade to the 5 bar valve for us systems. I believe the tank fittings are also metric/euro types (not npt) so you will have to get adapters. Size wise they are approximately the same size as the isotherm. So these water heaters are a little bit cheaper but you have to get extra stuff. I have noticed that many of these features (copper tank, and titanium heating elements) are used in high end US house water heaters. So I'm thinking maybe the marine market has not kept up with current trends. Again I haven't seen any comparison so I don't if it's worth while compared to an isotherm

Practical sailor did a water heater teat and isotherm was up at the top.

[Bill O]

We have a Raritan 12 gal. for many years that came with the boat and we just refurbished the element and anode. We added additional f/g insulation around the outside and it holds hot water for more than 24hrs.
While it is a work horse, my main complaint is the steel liner and the need for an anode. When the anode erodes away, the water can get smelly and possibly corrode the liner. With a SS tank, typically no anode to replace.
I was always impressed w/the old orange, pill-type Isotherm water heaters. They were well insulated and had a 750W element that could be run off an inverter to heat the water.

When I quickly looked them and it appears Isotherm and Isotemp may be both manufactured by Webasto. If I were to do a new install, it would be with an Isotherm/Isotemp unit.