The Offshore Voyaging Reference Site

A Tale Of Two Water Heaters

Last year our venerable and functional 9 gallon Allcraft water heater (on the right) finally bit the big one after 15 years of faithful service. And, wouldn’t you know it, Allcraft had gone out of business.

So, after some fairly perfunctory research—how big a deal could a water heater be?—we ordered a new stainless steel 10.5 gallon water heater from Atwood Mobile Products (now Dometic). Sadly it has turned out to be a disappointment and near useless to us for the following reasons:

  1. The thermostat can not be adjusted and is set way too cool. (We have an automatic temperature constant mixing faucet in the shower, so there is no danger of anyone getting burned if we set the thermostat a bit higher.)
  2. The minute that you use any of the hot water and it is replaced by cold water, the remaining water in the tank becomes barely warm. We think this is due to the heater’s squat square shape that brings the inlet and outlet too close together so that the incoming cold water mixes with the remaining warm water, instead of staying at the bottom of the tank, like it did in the old heater.
  3. Even after running the main engine for an hour and thereby causing 180 degree F (80 C) water to flow through the heater’s exchanger, the water in the heater is barely warm. (We know that hot water from the engine jacket is flowing through the water heater because the Webasco heat exchanger cabin heater plumbed in parallel still works fine and puts out as it always has.)

The result of the above is that we can barely get two showers out of the new heater before the water goes cold. And this “intrepid Arctic sailor” is a real wimp about cold showers. That’s why Phyllis, who is made of sterner stuff, always gets the second shower these days.

Contrast this with the old Allcraft that would after just 30 minutes of engine run time, easily do two hot showers, (indicating an efficient heat exchanger) and then provide plenty of hot water for the dinner dishes a couple of hours later. Even after all that, the water would still be warm in the morning!

So, three issues:

  1. In our opinion, and from our experience, the Atwood heater is pretty much useless in a boat installation, although I guess it would be OK if you were plugged in at a marina most of the time.
  2. Can anybody recommend a water heater that actually works in the real world of live-aboard offshore voyaging in which shore power is a rare luxury that happens maybe 10-20 nights a year? It would be really nice, although not vital, if it was fabricated out of stainless steel too, like our old Allcraft. If so, please leave a comment.
  3. Does anyone want to buy a slightly used Atwood water heater? Oh well, I guess not. Me and my big mouth.

As usual with this type of post we will contact Atwood to see if they would like to comment.

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I can’t yet offer you the benefit of any direct experience, but I can tell you where my research took me. The water heater I selected for the voyaging boat I am building is the Superstor SS012m. In its favor is a 316L stainless steel liner, relatively compact space requirements for its 12 gallon size, and a respectable 1/2° F per hour heat loss rating. I’ve also had passing conversations with a couple of users who are very satisfied with their purchase. I tripped into the one I purchased on Craigslist for a very satisfying price (in Maine nonetheless—timing is everything!). The best retail price I was able to find was through Defender. You can learn more at:


I have to ask, are you happy with your Superstor?

Brian Lockett

We’ve had good luck with Isotemp, good temp adjustment, all stainless, two useful configurations. Mfg by Indel Marine.

David H

Here in the UK a good calorifier can be obtained from Surecal. I have experience of two of their calorific heaters. Both are fully heated after approx 20 minutes of engine running. They feature a well insulated jacket which after 12 hours still retains reasonable heat. A pressure relief valve protects the system, and the in-built immersion heater (1kw; 240volt in our case) warms the tank quickly. A good feature is the balance valve that allows hot/cold mixing directly from the tank, thus preserving more of the heated water. An expansion device is crucial. A real bonus is they are really good value! Hope this helps?

Wayne Lukas


Allcraft was sold, the new owners will build water heaters on order. I recently purchased a 12 gal vertical heater from the original owner who has a few models stored in his garage after selling the business.

if you are still interested in purchasing an Allcraft heater, e-mail me and I will get you contact with the original owner as well as the new owners.

Wayne lukas

Doug M

Hi Wayne,

I have an H-9 (9 gallon) Allcraft heater which has served us pretty well for the last 7 years but has died (I beleive it is the element) and would like to get their information if I could. I know this forum is old but still hoping…

Cheers, Doug


You can get the element at Knox Supply in Chattanooga TN


I would be interested in contacting the new owners as I need a temperature sensor for my old Allcraft. It works fine except the sensor has gone bad.



I have a water heater that when I am hooked up to shore power every time I make the breaker to turn it on, I blow the fuse at the outlet on the dock. Any idea what is causing this?

John Haggis

will do, thanks.

Ed finn

The 6 gal Raritan cylindrical unit worked great for me…
It is in my 1985 C&C Since new…
The mounting screws/ flanges were too flimsy, and rusted out. But lots of hot water w/ Engine or electricity
… Still available from West. Marine @ $629.00 # 296394

Anders Juel

The Surecal has good mountings and it is a very, very good heater. Some of the features are mentioned in the mail above. It also has copper inside (never rust), several heating coils for electrical heaters and engine/hot water heaters.
They are available at Marinetec-us in Seattle.

Victor Raymond

I am considering either adding an external heat exchanger (20,000 btu double wall flat plate) to the current 230v hot water heater or a brand new Torrid hot water heater (with replaceable heat exchanger and elements.) Anyone have any experience with either of these two systems would love to hear your thoughts and experiences.
BTW Superstor is no longer producing marine grade HWHs so that option is out.
Thank you

Pat Kelly

Hi Victor, John

I am in the same boat, so to speak – my old 12 gal Allcraft water has bitten the big one. As has been noted here- Allcraft either is no more, or is no longer interested in supplying marine water heaters. In addition, I do not know why yacht designers put important systems in space and build boats around them; never considering that these systems need to be serviced and sometimes replaced. To remove the 12Ga Allcraft that sits under the refrigerator, I need to dismantle the dinette and hope that this will provide enough clearance to get the old Allcraft out and a replacement in. So, I would like some feedback on Torrid Water heaters (one has approximately the same dimensions as the Allcraft) as regards whether or not they are a viable replacement for the Allcraft.

I’d appreciate any thoughts

Best regards

Pat Kelly

Victor Raymond

Hi Pat,
I ended up buying the Isotemp SPA 30 Marine Water Heater since it was available in 230V and plastic rather than stainless (read stain later) insulating jacket. It also comes with a hot water mixer to help avoid hot water burns from excessively hot water (when using engine coolant).
Installation was straightforward.
Good luck

Pat Kelly

Thanks, Victor
That’s a great suggestion. I looked them up on the web and I think that the Isotherm SPA 40L unit would work just fine for my boat – and it’s a hellavalot cheaper! The problem with my old Allcraft (I think) was that they used bronze fittings connecting to stainless steel components. I’ll give this a try! Thnks very much.


Jim R

Do you have a “hot water loop” plumbed to save water? If so, do you have any pointers?
Jim R.

Robert Andrew

Well my Allcraft has (apparently) died as well after 30+ years service (with one factory check up after 15 years). I haven’t pulled it to inspect what’s happening, but assuming it is unrepairable, what is the best option these days?

Rob Gill

We bought an Isotemp as a replacement two years ago and so far we have been pleased with the performance. The coolant water from the engine seems to heat the new cylinder faster than the old one and the electrical heater element draws around 60A which allows us to heat enough water in summer using our inverter and solar in around 45 minutes, without significant battery cycling.

This new cylinder definitely holds the heat better than our last cylinder of the same capacity (20 year old Quick) with often a decent amount of hot water available next morning, but that could be to do with me lagging the new cylinder with an extra thermal blanket and also lagging the HW water system pipes.

Install was straight forward and everything was laid out logically giving good service access. Picture taken just before lagging installed.

IMG_3581 Large.jpeg
Rob Gill

Hi John,

Yes, bit confusing, sorry. The heater element runs on 230V at 750W through the inverter. So on summer days in NZ we typically see a net current draw of around 20A on our BMS display when manually running the water heater using 230V.

With our high solar gain, we often have 40A coming into the charge bus from the two solar controllers (record is 46A so far) from 660W flexible solar panels. We are often at 100% SOC by midday in summertime.

Still cycles the batteries a little, but for us nicer than running the engine at anchor. Our old Quick cylinder was 1200W, which meant we wouldn’t have time to get the benefit of our excess solar generation capacity to heat water.