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?

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.

Torrid.

With engine heating loop and, if you have it, another loop via your hydronic heating unit. No generator required.

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).

What about tankless water heaters? They seem small and you always have hot water.

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.

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...

-Chris

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

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.

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.

Mule said:

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.

Click to expand...

Now that is an interesting question.

djmarchand said:

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

Click to expand...

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.

Mule said:

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.

Click to expand...

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.

>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!

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.

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.

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.

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.

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.

Ski in NC said:

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.

Click to expand...

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.

If I need hot water, just run the gen for 20min.

20 min may create hot water but even with a 250A charging system it wont do much for the house batts.

Insequent said:

Torrid.

With engine heating loop and, if you have it, another loop via your hydronic heating unit. No generator required.

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Agreed. With our boat in BC heating via engine loop or genset is all we need. We could if desired hook up the hydronic heater loop. Replaced 20 gallon Seaward (junk construction) with a 17 gallon Torrid.

Boydster said:

Now that is an interesting question.

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The waste heat from a small genset cannot match the main engine waste heat and genset impellers are usually a lower head unit than what one would see on a main engine.

I replaced mine last winter with a 6 gal. Raritan with engine loop. Had a small problem with the 180 engine temp tripping the reset breaker after a run. Raritan was very good with replacement of the breaker AND follow-up after installation. I had a valve installed at the engine to cut off the loop easily, as the 180 water is too hot and the unit recovers in about 15 min. on A/C power. If I had it to do over, I would not have replaced with the heat exchanger option-I only did cause the old unit had it & was already plumbed for it. Could have saved about $100 bucks & I really don't plan on using the loop-only in a pinch. I am very happy with the unit.

>as the 180 water is too hot<

That is why folks install scald prevention devices.

Water Heaters

I installed a Quick Nautic Boiler water heater in my last boat. Stainless tank, urethane insulation, high efficiency heat exchanger. This was a nice unit for a reasonable price. It's worth taking a look to see if it meets your needs.

Interesting item and something to think about.

You Can Make A Difference..... - SailboatOwners.com

This would also allow you to set your t-stat on electric much higher giving you more effective hot water.

I found the unit at Home Depot solid brass and $70.00

3/4 in. Brass Hot Water Extender Tempering Valve - Lead Free-3/4 LF70A at The Home Depot

Torrid! I have a Torrid manufactured 10 gallon water heater on my boat that still cranks out the hot water. According to them the serial number dates to 1985! The only thing I have done is to replace a leaky T&P valve.

There's a UK company which selsl fully insulated double coil copper cylinder calorifiers with 1kw immersion elements in various sizes specifically designed for marine use.
They are asapsupplies.co.uk,
I appreciate there are shipping charges to consider, but when you've just spent zillions on your pride and joy what's a few more bucks in comparison for the comfort ?

They are nice looking units indeed. http://www.asap-supplies.com/marine/boat-hot-water-heaters/supa-hotpot-twin-coil-calorifier-520330