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Old 10-11-2014, 01:04 AM   #1
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Water heater recommendations

Our Raritan water heater is about due for replacement. Gotta' say I was a bit overwhelmed by the selection that's available out there nowadays. Wondering what the collected wisdom here would advise. Thinking 8 - 12 gallon capacity with a vertical tank. Recharge time? Insulation? Amperage draw? Corrosion resistance?... Suggestions?
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Old 10-11-2014, 04:44 AM   #2
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Water heater selection is influenced by whether you spend your time in marinas with available shore power and shore water or whether you anchor out. If you anchor out most of the time there is a difference as to whether you are moving from place to place or sitting for days in one anchorage. The size of your generator is also a factor if you regularly anchor out.

The power draw of most North American (110v) units is either 1500 watts or 750 watts. At 1500 watts it may take as much as 15 minutes to heat a 6 gallon (US) tank, whereas it may take 30 minutes for 750 watt 6 gallon unit. A 1500 watt unit, a couple of chargers and normal household draws will load an 8kw generator to the point the hertz will start dropping. In a 60 hertz environment a drop to 57 hertz may or may not be a problem depending on your non-water heater appliances.

For this reason some boaters prefer the 750 watt water heaters.

As to size 6 gallons of fairly hot water is satisfactory to many boaters who anchor out most of the time. At anchor water is heated twice a day when the generator is run.
Others prefer 8 to 12 gallon units and larger. The larger the unit the longer the generator run time to heat up and the more space it takes in the engine room.

Two very good brands are Isotherm and Raritan.
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Old 10-11-2014, 05:52 AM   #3
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Torrid.

With engine heating loop and, if you have it, another loop via your hydronic heating unit. No generator required.
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Old 10-11-2014, 07:05 AM   #4
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Just installed the Iso-temp SPA 30 8 gallon...very pleased.

I think it's the right size for the 750 watt element (you can change or order with the 1500 watt element.

Being foam surrounded and stainless tank gave me a bit more piece of mind than an aluminum tank and glass wool insulation that can get wet and be no insulation or it packs down/falls away after time.

Have let one person take a fairly long hot shower, and still had enough for a second short shower within 15 minutes...haven't run it out yet so hard to say what it's real talent is.

The construction, ease of install were nice and it says horizontal or vertical install.

This is their mid-priced version and seems just fine. (a little less than $500).
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Old 10-11-2014, 08:33 AM   #5
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What about tankless water heaters? They seem small and you always have hot water.
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Old 10-11-2014, 09:01 AM   #6
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The Raritan 1700 series water heaters have a recovery rate of 13 gallons/hours. They are good water heaters so replacement may save some head aches since that is what you have now.

Torrid Marine water heaters are also a good product. These are glass lined and come in horizontal and vertical models.
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Old 10-11-2014, 10:41 AM   #7
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Ours is an Atwood, 11-gallon model. It works. We've never run out of hot water during showers. Can't compare to others, though; no experience...

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Old 10-11-2014, 11:28 AM   #8
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Isotherm has a stainless steel tank and is one of the few or maybe the only marine hot water heater available with two coils to do what Brian suggested: one coil for you engine jacket water system and one for your hydronic heating system.

Whether that helps of course depends on whether you have a hydronic system and if it is cold enough to fire it up.

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Old 10-11-2014, 02:24 PM   #9
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Another vote for the isotemp spa 30. Installed this spring to replace a leaking Raritan unit. Easily supplied enough hot water for the two of us on the hook all summer. We run our 8kw gen for an hour in the a.m. and an hour in the p.m. to charge batteries and heat water. Very easy install, ours is horizontal against the front engine room bulkhead. Defender had a reduced price.
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Old 10-11-2014, 09:02 PM   #10
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Here is the question... In most circumstances when you really need hot water you are at anchor or at the slip hard wired. Should not your loop not be to your main but to your generator thereby cutting generator run time? Just thought.
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Old 10-11-2014, 09:33 PM   #11
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Quote:
Originally Posted by Mule View Post
Here is the question... In most circumstances when you really need hot water you are at anchor or at the slip hard wired. Should not your loop not be to your main but to your generator thereby cutting generator run time? Just thought.
Now that is an interesting question.
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Old 10-12-2014, 12:44 AM   #12
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Quote:
Originally Posted by djmarchand View Post
Isotherm has a stainless steel tank and is one of the few or maybe the only marine hot water heater available with two coils to do what Brian suggested: one coil for you engine jacket water system and one for your hydronic heating system.

Whether that helps of course depends on whether you have a hydronic system and if it is cold enough to fire it up.

David
Install a 'summer loop' into the hydronic system. It bypasses the full hydronic circuit. That way you aren't heating the whole boat if all you want is hot water. Basically gives you hot water on demand, at the dock or at anchor. The Webasto (hydronic) furnace doesn't need to run for long.
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Old 10-12-2014, 05:19 AM   #13
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Quote:
Originally Posted by Mule View Post
Here is the question... In most circumstances when you really need hot water you are at anchor or at the slip hard wired. Should not your loop not be to your main but to your generator thereby cutting generator run time? Just thought.
Have thought of doing this for years, as my generator is run much more often then the main engine. In addition to the question of the plumbing, my current use of the generator for battery charging provides us with plenty of extra power to heat the water. Thus I have never bothered with heating water using the generator's coolant system.
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Old 10-12-2014, 08:00 AM   #14
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>Should not your loop not be to your main but to your generator thereby cutting generator run time?<

Would depend mostly on how over sized the noisemaker is.

If it is operating at minor load another 15A will help with efficiency and engine life.

If it is at 80+ % much of its life , co generation would be a great answer , load free HW!
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Old 10-12-2014, 08:47 AM   #15
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I was thinking more in terms of quick hot water with both the antifreeze loop and the heating element working to heat the water thereby shorting the needed genset run time. In my case I need the run time to produce that 6 gallons an hour my water maker produces.
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Old 10-12-2014, 08:53 AM   #16
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On the hook our gen has to run anyway, so I think in our case wiring is easier and more reliable than a ten foot run of heater hose each way. We also have a plan B for hot water if the gen doesn't start... the Lehman can charge the batteries and heat the water with a bit more noise, but the trip isn't over.
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Old 10-12-2014, 09:26 AM   #17
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I am genset free except for hot water. The air conditioner, TV and microwave. Otherwise w/735 watts solar, 400 wind and 1125 amps battery I need little from genset. That is why I was/am looking for quick hot water.
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Old 10-12-2014, 03:56 PM   #18
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Does anyone know how much time a diesel engine takes to heat a 6 gallon water tank if the coolant loop is connected to the heat exchange in the water heater?

Would be interested to compare the run time with the 15 minutes my 1,500 watt heater element takes.
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Old 10-12-2014, 04:30 PM   #19
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If diesel is already hot, water tank should warm up quick, like 10min or so. If you have to warm up the diesel AND the tank, more like half hour or so.

I just run a small domestic water heater with no loop from engine. Engine is sacred so I don't want to compromise its cooling system with a nicety. If I need hot water, just run the gen for 20min.
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Old 10-13-2014, 05:36 AM   #20
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Quote:
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If diesel is already hot, water tank should warm up quick, like 10min or so. If you have to warm up the diesel AND the tank, more like half hour or so.

I just run a small domestic water heater with no loop from engine. Engine is sacred so I don't want to compromise its cooling system with a nicety. If I need hot water, just run the gen for 20min.
Assuming these run times are reasonably accurate, it confirms my feelings that for those of us who anchor extensively and do not move every couple of days that a small water heater heated by the generator is a good compromise. Running the generator to charge the battery will heat the water. A larger water heater say 20 gallons would take 45 + minutes. In addition to a run time which may or may not be what is needed for the batteries a 45 minute run time means you have to schedule your shower if you haven't run the generator lately.

For us there are times we come back to the boat and need a shower and have one in 15 minutes after heating the water.
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