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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems > Inverter for hot water tank
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Thread: Inverter for hot water tank Reply to Thread
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Topic Review (Newest First)
05-31-2013 11:17 PM
mitiempo
Re: Inverter for hot water tank

I have been to that link before and it looked to be the best available. But they do not say whether it actually meets ABYC standards, only that it must be installed to those standards. ABYC wants a totally enclosed combustion chamber that is not open in any way to the boat interior. Also pilot lights are not allowed. On the entire site I couldn't find any pictures of the water heater.

If it can meet the standards, possibly by installing it in a vented locker like a propane tank, it might work. I once owned a Rinnai water heater and instant propane water heaters are the most convenient as far as use. You just have to be sure your insurance company is ok with it.

From their website:
05-31-2013 11:09 AM
rmeador
Re: Inverter for hot water tank

I'm not a marine professional and I have not read the ABYC standards, but my understanding is that most vented on-demand propane water heaters will comply if they are installed in accordance to the ABYC standards -- it's less about the heater itself and more about the installation. That could be a load of crap, I don't know, I haven't done a ton of research into it. This was one of the first that my googling turned up, and the specs seem to imply it can be installed according to ABYC standards: ShowerMate M-550 ? Marine Tankless Water Heater - PrecisionTemp

My friend who has one on his boat is away cruising at the moment, so I can't ask him what brand he has.
05-30-2013 11:21 PM
mitiempo
Re: Inverter for hot water tank

Quote:
Originally Posted by rmeador View Post
I'm rather confused... your engine circulates its coolant water through the hot water heater, right? But this isn't hot enough for a shower? I realize that having a raw-water cooled engine will likely make it not as warm as the fresh water circuit on my engine, but even the raw water coming out my exhaust is plenty warm enough to shower with (I'd guess about 90 degrees). This isn't what you see?

I plan on having an on-demand propane hot water heater on my next boat for infinite showers, you might want to consider that. There is at least one model approved for use on boats.
A salt water cooled engine has a 140 degree thermostat. But the raw water used to cool the engine doesn't recirculate as with a closed fresh water/antifreeze system and is brought in cold and sent out the exhaust before it gets hot and especially in a cold water area it may never get very hot. You will get luke warm water after a lot of engine time. With the closed fresh/antifreeze system after running for a very short time the coolant is 180 degrees and will heat a tank quickly.

Which on-demand propane water heater is meets ABYC standards for marine use?
05-30-2013 12:17 PM
rmeador
Re: Inverter for hot water tank

I'm rather confused... your engine circulates its coolant water through the hot water heater, right? But this isn't hot enough for a shower? I realize that having a raw-water cooled engine will likely make it not as warm as the fresh water circuit on my engine, but even the raw water coming out my exhaust is plenty warm enough to shower with (I'd guess about 90 degrees). This isn't what you see?

Others have pretty thoroughly explained the power problems with electrically making hot water while under way, but there's another aspect that hasn't been brought up yet. Even if you did heat your water with electricity, without some plumbing changes, you're still pumping your insufficiently-warm raw water through the hot water heater, which will actually be cooling your hot water!

I plan on having an on-demand propane hot water heater on my next boat for infinite showers, you might want to consider that. There is at least one model approved for use on boats.
05-29-2013 07:13 PM
tibtib
Re: Inverter for hot water tank

Quote:
Originally Posted by JimsCAL View Post
Unfortunately, this doesn't change the amount of energy that a battery can store and how much water it could heat. Those low wattage elements will only increase (signficantly) the time it takes to make hot water.
That's true, but a 200-watt DC element would draw less than 15 amps and would make it possible (but slow) to have hot (at least lukewarm )water while motoring.
05-28-2013 07:59 PM
Bene505
Re: Inverter for hot water tank

You could always use a lower wattage heater element.

Now that I'm use my extra solar power to get the freezer extra cold... (Goal is no battery usage for the freezer at night.) I'm thinking about running my extra solar to an inverter, driving a lower wattage 120v heater element. It's extra energy anyway, so efficiency matters less.

Regards,
Brad
05-28-2013 06:17 PM
JimsCAL
Re: Inverter for hot water tank

Quote:
Originally Posted by tibtib View Post
Another option would be to convert the water heater to 12 volt operation by changing the element. Here's an example 6 Inch 12 Volt DC Submersible Water Heater Element 6 Inch 12 Volt DC Submersible Water Heater Element [430] - $49.98 : Missouri Wind and Solar, DIY Wind and Solar Energy
Unfortunately, this doesn't change the amount of energy that a battery can store and how much water it could heat. Those low wattage elements will only increase (signficantly) the time it takes to make hot water.
05-26-2013 02:17 AM
tibtib
Re: Inverter for hot water tank

Another option would be to convert the water heater to 12 volt operation by changing the element. Here's an example 6 Inch 12 Volt DC Submersible Water Heater Element 6 Inch 12 Volt DC Submersible Water Heater Element [430] - $49.98 : Missouri Wind and Solar, DIY Wind and Solar Energy
05-20-2013 10:44 AM
pdqaltair
Re: Inverter for hot water tank

Another way to look at it:

A typical deep cycle battery can store about 1.800 kw-hr of energy or about 6100 BTUs. However, only 40% of this safely useable, so about 2440 BTUs.
Warming 10 gallons from 65-105F takes about 3300 BTUs.

Thus, each shower would flatten about 1 1/2 batteries. Different showers and different batteries change the calculation.

Batteries just don't store that much energy, not like liquid fuels (130,000 btus/gallon for diesel). Only a fraction of an ounce of fuel per charge cycle, the challenge of electric drive.
05-20-2013 10:16 AM
rikhall
Re: Inverter for hot water tank

Again, Maine Sail to the rescue. Numbers I can understand.

Thanks mate. It just seemed like a good idea at the time.

We go in the water Thursday. Masts go up on Saturday.

Rik
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