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  #1  
Old 06-27-2010
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Hot Water Heater what size/type?

Currently we have a Gas (LPG) hot water system that is getting very old, am looking at getting away from the gas system, I thought about a 50 litre, what size does everyone else have, also all these are 240 volt/ 750 watt, so do you just run it through an inverter?? would'nt they use a lot of power?
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I'm not aware of anyone that runs a 120v water heater through an inverter, for the reason you mention.

Most boats I've seen have a combination of 120v (for use at the dock) and engine coolant (a hose carries the hot "coolant" from the engine, through a heat exchanger in the heater, and back to the engine) in one unit.

There are also diesel-fired heaters (Webasto, Espar) which, in addition to heating the water, can heat the boat. We have one of those and have found it very handy. Compact, low power draw, and reliable. Some folks just go with a teakettle, or some sort of coil that sits on the stove or diesel heater.

The size you want will depend on your demands, but about 6 gallons seems to be common. With really good insulation you could have a larger tank and heat it up (by running the engine or the diesel heater) every 2nd or 3rd day instead of every day, but of course, that takes more space.
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Old 06-27-2010
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point source water heating

I would recommend looking into a point source water heating either propane or diesel fired.

No hot water tank, all the hot water you can use till your fuel runs out.

Wb
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Old 06-27-2010
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Most on-demand instant water heaters are not marine rated, and many are forbidden by insurance regulations, so you need to check with your insurance company if you want to go that route.

As for regular, tank-based water heaters. The most common size is about 6 gallons. Usually the hot water heater has a hydronic heating coil so that it can be heated using the engine coolant. Most will also have a heating element for when the boat is connected to 110 VAC shore power.

One thing to really watch out for with the hydronic, engine coolant heat exchanger type units is the water temps are often far hotter than you'd find in a domestic water heater and you're likely to scald yourself if you're not extremely careful. I'd recommend adding a tempering valve to keep the water temps in a reasonable range and prevent the risk of scalding.
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Old 07-11-2010
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hello Mjak, It really depends on how you use your boat and what you want hot water for. If you're always at the dock, plugged into shore power, definitely get an electric hot water heater. If you anchor out and run your engine to charge your batteries, then get one with an engine heat exchanger so you get hot water for shower and dishes at the same time you generate power. If you have solar and/or wind generator for generating power, you can still get hot water from engine heat exchange just from the time you're motoring into an anchorage. Make sure you get a marine water heater, such as Raritan (don't know what they have in land of Oz). On our 25-year-old boat the previous owner had installed a cheap Sears electric hot water heater to save money, and it had rotted out in the marine environment. My advice is to get as big a water heater as you have room for. The water will stay relatively hot, especially in warm environments, and make everyone happy to have a bit of hot water for a navy shower, etc. Also, a 20-gallon hot water heater increases your water capacity by 20 gallons....
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Old 07-11-2010
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750 watts is well within the capabilities of a decent size invertor. A large battery bank is a given but many use an invertor for hot water when away from the dock.
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Old 07-12-2010
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Thanks everyone, bought a 24Lt Isotemp Basic, dimension size was the deciding factor, with just the 2 of us most of the time, 24 lt mixed with the warm water out of the tank at say 4:1 will give us plenty, will be quicker to heat up as well. its all stainless as well which I need with my saltwater cooled yanmar 27hp 85' circa. may have to mount it above engine height, read a post somewhere about mounting higher you need a vent or something??? not sure
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Old 07-12-2010
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Quote:
Originally Posted by sailingdog View Post

One thing to really watch out for with the hydronic, engine coolant heat exchanger type units is the water temps are often far hotter than you'd find in a domestic water heater and you're likely to scald yourself if you're not extremely careful. I'd recommend adding a tempering valve to keep the water temps in a reasonable range and prevent the risk of scalding.

This is spot on. I have been working Eric J. of the ABYC now for quite a while to get this addressed. It has supposedly been run up to committee and discussed and I am waiting to hear back from him.

The problem is much bigger than just hot water heaters getting to 180 degrees or higher. There are compounding issues of inadequate PVC hose max rated at 150 degrees being connected to 180 degree+ hot water heaters. When this happens the PVC hose can soften, bubble and burst or soften and deform enough to be blown right off a hose barb. The latter actually happened to us on a BRAND NEW 2005 vessel, in July of 2005, leaving us with no domestic water many miles from any source of it.

Scalding can begin at 140F and actual burns at 190F. An engine with a 180 degree t-stat running a slight restriction can EASILY get over 190F.

On more than one vessel I have seen 210F T&P valves blowing off on temp due to engines running hot doue to a bad t-stat, clogged intakes or restricted flow of raw water!! 210 degree water or an engine running at 210+ are 100% not acceptable and totally unsafe.

Residential plumbing has codes that prevent scalding hot water yet the marine industry has yet to address this when water is heated off an engine, perhaps because the builders don't want to pay an extra $20.00 for a tempering valve.

The water heater the OP bought is one of the few good ones that come standard with a tempering valve to limit scalding..

If you feel as strongly as I do about this dangerous issue, unregulated HOT water that can scald or burn adults or kids, or if you have been personally scalded or burned as I have, please voice your concerns to the ABYC and let them know this should be considered an UNACCEPTABLE practice..

IMO EVERY hot water heater that has the capability to be heated via a marine engine should be MANDATED to be sold with a tempering valve to regulate the hot water output temperature. HOPEFULLY the ABYC and the marine industry do the right thing, and YES I am an ABYC member..

Unregulated engine heated hot water heaters should have been banned LONG ago and SHAME on the companies who don't voluntarily include them as standard equipment as IsoTemp does!!!

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Last edited by Maine Sail; 07-12-2010 at 08:29 AM.
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