Isotemp and Super Stor Earn Best Ratings Among 7 Water Heaters

The Super Stor heated water fastest, and the Isotemp kept it warm longest.


When one compares the list of standard equipment on a boat built in the late 1980s or 90s to a boat built during the 60s or 70s, the differences are striking. Back then, lifelines, stanchions and pulpits often cost extra. But everybody wanted them, so builders moved them from the option list to the standard equipment list. In the category of plumbing, builders now routinely install pressure water systems, shower basins and water heaters. Its a major reason boats cost more today.

Most water heaters installed on 28′ to 50′ boats are of the storage type that operate either by 120-volt AC shore power and a heating element in the tank, or by using hot water from the propulsion engines cooling system circulated through a heat exchanger in the tank.

Occasionally, one sees instantaneous propane water heaters, such as the Paloma, Bosch, Aqua Star or Wolter (bought a few years ago by SPS Systems, now presumed out of business), but the dangers of carbon monoxide poisoning and oxygen depletion have scared many manufacturers away from the marine market. The reason is that boats are more airtight than country cabins. And, of course, owners had their reservations about the dangers, too. While we have lived aboard for many years with a propane water heater without problems, we acknowledge that added caution is required. A carbon monoxide detector is a good idea (see November 15, 1998). We have reported on these heaters in the past and will continue to, if and when developments occur.

In the meantime, we decided to update our March 15, 1991 test of storage-type water heaters. For this report we obtained seven models from Raritan Engineering, Isotemp, Atlantic Marine, Allcraft, Seaward Products and two from Isotemp. We tested 6-gallon models, though all of the companies make larger ones.

In 1991, we tested the heaters only with their 120VAC heating elements. This year, we were prepared to do the same, but in discussions with the various manufacturers, we were told we would find greater differences if tested with the heat exchangers, owing to differing designs.

Circulating engine-temperature water-about 160F to 180F- presented something of a logistical problem. First you have to make hot water, then keep it running through the tank, round and round. Before scratching our heads too long, we figured the easiest way to do this would be to hook each tank up to a real engine. Not easy in a boat. But fortunately, our neighbor in the Ted Hood Marine Complex in Portsmouth, Rhode Island, Kiwi Marine Services, just happened to have a rebuilt Perkins 4.108 sitting on the shop floor. And Dan Kerr, proprietor, still had the diesel fuel and water tanks set up from last years genset test. No problem, he said.

The Test
In Kiwi Marine Services shop, each water tank was set on the floor next to the engine and plumbed, that is, with two hoses from the engines cooling system attached to the heat exchanger fittings on the water heater tank. A sensitive thermometer with a 6″ probe was installed in each tank so that readings could be made without drawing water out of the tank (a practice which on a boat introduces cold freshwater each time and dramatically advances heat loss). Our tests, therefore, created ideal conditions that would probably not be duplicated in real usage.

Then, the tank was filled and all air bled out.

The engine was started and run for 5 minutes at 1,000 rpm, after which time it began to warm as evidenced by the temperature gauge. After 5 minutes, engine speed was advanced to 2,000 rpm. Maximum temperature of the engine cooling water was 165F. The engine was run for 1 hour and shut off. Temperature readings of the tank water were made each 5 minutes while heating up, and at 1 hour intervals cooling down.

The results are shown in the graphs above. Note that all heaters have pressure relief valves so we did not include that information in the Value Guide or in the product descriptions.

Allcraft V5SS
It would be difficult to find a more beautifully made heater than the All-craft. Its case is 304 stainless and the tank is 316. Workmanship is excellent. The inlet and outlet plumbing fixtures are copper. The rugged electrical components are easily accessible behind a hinged cover. It was the only heater that came with wiring pigtails, which should be run to a nearby junction box. The thermostat is adjustable.

The Allcraft has three welded feet or tabs for through-bolt mounting. It should be remembered that when full, these tanks weigh about 75 lbs. For our last report, we were warned by manufacturers that tabs of this type may not be sufficiently strong to secure the tank in rough conditions. As a precaution, it is recommended that the tank be strapped down, much like batteries.

Unlike most of the other heaters, which have pressure relief valves protruding directly into the tank, the Allcrafts valve is plumbed to the hot water outlet. This takes up a bit more space, but eliminates another hole in the tank.

The Allcrafts performance is only average. This may be due to its fiberglass insulation. The V5SS heated to 138F after 1 hour and had cooled to 114F after 8 hours. After 22 hours, it was 78F.

Bottom Line: The Allcraft is possibly the best made tank we tested, but very expensive at $689. For that price, wed like matching performance. The heater comes with a 10-year warranty, best of the group. And it holds more than advertised-5.75 gallons. One tends to trust a company that understates its specifications.

Atlantic Marine R6E
Atlantic Marine is a comparatively new company that makes a wide range of marine water heaters, including square models in stainless steel and fiberglass, and round fiberglass models. We were going to test their top-of-the-line stainless heater until the company told us that the fiberglass models outsell the stainless ones by 10 to 1. They are made in Costa Rica with white gelcoat exteriors.

Mounting is through holes in the round, molded base flange of the heater. The tank is steel, lined with polyester, protected by a magnesium anode. Insulation is polyurethane foam. The thermostat is fixed; an adjustable version is available.

Measured tank capacity was a gallon less than advertised-5 gallons.

The R6E heated water to 140F after 1 hour, and cooled to 96F after 8 hours, 74F after 22 hours.

Bottom Line: Priced at $244.95 discount through Defender Industries, this, along with the Seaward, was the least expensive unit tested. It was the third slowest to heat and the second fastest to cool. Wed spend an extra $50 for one with better performance.

Isotemp 0221R and 0221M
The Isotemp heaters are made by Thermoprodukter AB in Kalmar, Sweden and distributed in the U.S. by Great Water of Erie, Pennsylvania.

Both models are identical except that the 0221M or Magic unit has a tube in the tank filled with a eutectic solution that is supposed to keep water warmer longer. Presumably, this accounts for its extra weight.

The tanks are 316 stainless steel and surrounded by polyurethane foam with a hardened finish. It is a peach color and is fairly rugged though it can still be dented with an errant blow of a tool. The heater lies horizontally, banded to two chocks that double as mounting feet. This was by far the most robust mounting system of the units tested.

A unique feature of both models is a mixing valve that circulates water from the top to bottom via an external hose. This provides for a more uniform temperature inside the tank.

The two models reached temperatures of 145F and 146F after 1 hour. Only two other heaters reached hotter temperatures (Raritan and Super Stor).

During the heat loss test, the 0221R cooled to 114F after 8 hours-good, but not quite the best. The next morning, 22 hours after the engine had been shut down, its water temperature was a remarkable 102F, making it the only one with water warm enough to shower (though you wouldnt want to mix it with cold water). The Magic model, which should have been even better, cooled at about the same rate as the R model for the first 8 hours, but after 22 hours was considerably colder than the R model. In discussing this with Great Water and Thermoprodukter, the feeling was that the water had not been heated long enough to completely melt the eutectic brine solution. Rather than storing heat, perhaps it drew heat away from the water.

To determine whether the concept indeed works, we retested the 0221M with its 120VAC heating element, allowing it to heat for 24 hours. Maximum temperature was 144F. After shutting off power, water temperature was 110F after 16 hours, and 111F after 22 hours, or 9F hotter than the 0221R heater. We believe the melting of the brine solution did retard cooling, but at $648 compared to $405 for the R model, this performance comes at a premium.

The thermostat cuts out at 167F and the overheat protection trips at 194F. They are not adjustable.

Volume was measured at 5-1/2 gallons.

The four-language manual is poorly done. You get the same one for either R or M model, despite differences in the units.

Bottom Line: The Isotemp heaters, available at discount from Defender, were best at retaining heat. Their peach-colored polyethylene covers show dirt and dings, but then water heaters are tucked away under cockpits and in engine compartments where they are seldom admired. And they are expensive. But if you want to take a hot shower the morning after arriving at an anchorage, without reheating water, these are the only two that will make it a warm one.

The Raritan 1700
Raritan Engineerings water tanks have been one of the most popular brands during the past several decades. They work well and are reasonably priced. A drawback of older models, however, was the painted steel case, that inevitably rusted. That has changed, now that a polymer case is used.

The tank is still glass-lined steel, which is less expensive than stainless steel, and requires an anode to prevent corrosion. Because glass and steel have different coefficients of expansion, it is possible to develop cracks in the glass, allowing water to contact the steel. Raritan still believes this is a better way to make tanks than stainless steel, which also can develop leaks if the welds arent done precisely or the metal properly passivated. Bad welds will be difficult if not impossible to repair.

Raritans plumbing fittings are galvanized. Insulation is a black foam sheet fitted to the tank. Company literature touts it as CFC-free.

The thermostat is adjustable.

The Raritan 1700 heated water quickly, reaching 148F after 1 hour, tied with the Super Stor (actually 149F) for the highest of any heater tested. After 8 hours, water temperature was 108F, but only 74F after 22 hours. It would appear, then, that it could be better insulated.

Bottom Line: At $269.95 discount, the Raritan 1700 series are fairly priced compared to the competition and reflect the use of more economical materials. They heat quickly, but are only average in retaining heat.

Seaward S700
Seaward makes water heaters with both galvanized steel and stainless steel cases. We tested the S700 with a stainless case. The tanks and heat exchangers are aluminum. Because galvanic corrosion is a concern with aluminum the 1-year warranty does not apply unless a galvanic isolator is installed in the ships electrical system.

The stainless case is in several parts and is screwed together. Workmanship is generally neat. Insulation is fiberglass. The heat exchanger tubing is on the backside, but can be special ordered on the front. Hot and cold plumbing fittings are galvanized. Mounting is through welded tabs. As with the Allcraft, additional strapping may be required.

The heater has a high temperature limit switch; the thermostat is not adjustable.

The S700 did not do well in our heat rise and loss tests. Maximum temperature achieved after 1 hour was just 121F, by far the lowest of the group. After 8 hours, it had fallen to 94F and to 75 after 22 hours.

Bottom Line: At $249.99 discount from West Marine, the Seaward S700 is, along with the Atlantic Marine model, the lowest priced heater in our test. For an extra $50, you can get much better performance. Not recommended.

Super Stor
Made by Heat Transfer Products, the Super Stor has a polymer case, polyurethane foam insulation and a 316 stainless steel tank. The heat exchanger is cupro-nickel and the plumbing fixtures are copper. The choice of materials ranks the Super Stor with the Isotemp and Allcraft heaters for overall quality. The mounting tabs, however, are angled pieces of stainless that the installer screws on to the case. We don’t think these are adequate to hold the tank, so recommend additional strapping.

The thermostat is adjustable.

In the tests, the Super Stor was easily the fastest to heat, up to 149 after 55 minutes. Between the 10- and 15-minute mark, it jumped a whopping 30F to 117F, meaning you wont have to run the engine long to get water hot enough for a shower. After 8 hours cooling, the temperature was 122F and after 22 hours it was 86F.

Bottom Line: Priced at $299.95, the Super Stor is our Best Buy. It uses quality materials throughout, heats fast, and retains heat better than all but the two Isotemp heaters.

Our only criticism of it is the flimsy mounting tabs and the absence of packing material in the shipping carton; ours arrived with a bent copper pipe.

If we learned one thing from this test, it is that theres more to marine water heaters than meets the eye. The heaters with polyurethane foam insulation generally held temperatures better than those with fiberglass insulation or other types of foam. The higher cost units have copper plumbing fixtures rather than galvanized steel. Stainless steel cases are pretty to look at, but the new polymer cases eliminate the possibility of corrosion, even if theyre not as robust. Most damage to any heater is likely to occur during installation; after that, the only enemy is corrosion. So, if you don’t care what the heater looks like, you can save money by buying one with a polymer case.

All of the heaters tested come with pressure relief valves either factory installed or easily installed at the time of installation. Attention should be paid to wiring, especially warnings about grounding. One, the Atlantic Marine, warns that because the heat exchanger is single wall for highest efficiency, failure of the exchanger could introduce toxic engine coolant into the drinking water system. With any of these heaters, any taste of coolant in the water should be regarded as a serious danger signal.

The easiest way to damage your heater is to turn on the electrical heating element in an empty tank. Some elements are incolay-sheathed to help protect them from dry-tank burnout.

Among the group of seven heaters, the two Isotemp models represent the most innovative thinking. The mixing valve appears to work well, and despite the appearance of the external foam case, these heaters retained heat better than the other five. The Magic models use of a eutectic solution to retain heat longer seems to work, but not well enough, in our opinion, to justify its $648 price. We think the 0221R model works just fine.

The Super Stor was something of a surprise, heating water as quickly as it did. The companys name, Heat Transfer Products, implies it knows more than a little about the subject of heating water. To save money, wed forego a stainless case for a good polymer case like the Super Stors, and all of its other components are corrosion resistant. Its our Best Buy.

Among the remaining models, the Allcraft is a thing of beauty, but priced too high for most boat owners. If only its performance matched its handsome good looks.

The Raritan is a fairly priced, reasonably performing heater. The Atlantic Marine was a bit of a disappointment, as was the Seaward, the only heater we really can’t recommend. This is unfortunate, as several years ago we gave the Seaward cooking stove top ratings, and have always found the companys customer service to be excellent.

Contacts- Allcraft Corp., 10 Liberty Way, Franklin, MA 02038-2556; 508/541-9133. Atlantic Marine, 8790 Park Central Dr., Richmond, VA 23227; 804/264-1169. Isotemp, Great Water Inc., 3684 1/2 West Lake Rd., Erie, PA 16505; 814/838-0786. Raritan Engineering, 530 Orange St., Millville, NJ 08332; 609/825-4900. Seaward Products, 3721 Capitol Ave., Whittier, CA 90601-1732; 562/699-7997. Super Stor, Heat Transfer Products, 120 Braley Rd., East Freetown, MA 02717; 508/763-3516.

Practical Sailor has been independently testing and reporting on sailboats and sailing gear for more than 45 years. Supported entirely by subscribers, Practical Sailor accepts no advertising. Its independent tests are carried out by experienced sailors and marine industry professionals dedicated to providing objective evaluation and reporting about boats, gear, and the skills techniques required to cross oceans. Practical Sailor is edited by Darrell Nicholson, a long-time liveaboard sailor and trans-Pacific cruiser who has been director of Belvoir Media Group's marine division since 2005. He holds a U.S. Coast Guard 100-ton Master license, has logged tens of thousands of miles in three oceans, and has skippered everything from pilot boats to day charter cats. His weekly blog Inside Practical Sailor offers an inside look at current research and gear tests at Practical Sailor, while his award-winning column,"Rhumb Lines," tracks boating trends and reflects upon the sailing life. He sails a Sparkman & Stephens-designed Yankee 30 out of St. Petersburg, Florida.


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