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Old 26-06-2010, 23:22   #1
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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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Old 26-06-2010, 23:47   #2
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Originally Posted by ozmike View Post
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?
I have a five gallon WH (19 litres), and it runs on 110V or off the engine. I run it on dock power, or off the engine when anchored or moored.
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Old 27-06-2010, 00:16   #3
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thanks jiffylube, 19 litres is that big enough? I guess the bigger the unit the more power, longer to heat it all, need a size big enough for the 2 of us. Are they like a household unit once hot they hold their heat. I guess if you need to do the dishes can always boil the jug, the good thing about the gas is it is quick, flick it on and you have instant hot water, what was steering me away from gas, is we will be heading off cruising instead of just weekends away, and gas supply could become a problem.
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Old 27-06-2010, 15:17   #4
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thanks jiffylube, 19 litres is that big enough? I guess the bigger the unit the more power, longer to heat it all, need a size big enough for the 2 of us. Are they like a household unit once hot they hold their heat. I guess if you need to do the dishes can always boil the jug, the good thing about the gas is it is quick, flick it on and you have instant hot water, what was steering me away from gas, is we will be heading off cruising instead of just weekends away, and gas supply could become a problem.
19 litres is large enough for two people if you take short showers. The electric unit I have has insulation wrapped around the tank, and it will keep the water reasonably hot for an hour or two after heating. It takes about 20 minutes of engine run time to get the water hot at anchor, but as long as you're motoring it's always hot (radiated heat from the engine). Dock side hooked up to electricity the heating element heats the water up in about the same time, but it will stay hot if you leave the unit running.
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Old 27-06-2010, 18:59   #5
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Size is pretty much determined by the space available for the water heater. Don't forget it must be strapped down or secured so that it cannot "fall off" or move around when you boat is "trashing and bashing" in big seas.
- - If you set the thermostat to a higher setting then you will be using less hot water and mixing more cold water which reduces the need for a large hot water heater. But primary consideration is where you are going to put the thing and how you are going to tie it down.
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Old 27-06-2010, 19:57   #6
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We started out with a 12 gallon heater, heated by dockpower or the engine, and replaced it with a 6 gallon unit, which is still plenty big enough for two people. Remember that you will not be taking long showers when living on the hook, as water is a scarce resource.

The engine heats the water to where we have to mix in cold in about 45 minutes, and the water is still warm enough for a shower 24 hours later.
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Old 30-06-2010, 12:35   #7
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Space is typically the determining factor here. But I can attest to the 6 gallon being large enough. Thats what we had on our last boat and it was fine for two adults and two kids. I can't recall us ever ranning out of hot water, but we try to be conservative with fresh water use in general. We got hot water pretty quickly from the engine running. IIRC you could take a shower after 10-15 mintues of engine use and it would stay warm enough to shower the morning after a decent motor running. Mine did not have any temperature control other than an emergency over pressure valve. It would make extremely hot water after a good bit of motoring such that we added lots of cold water to avoid getting burnt!

My current boat had a CNG fired unit but I have removed it because the insurance company required me to. The unit I had (Aquastar I think?) used a pilot light which is not ABYC friendly. There are newer "on demand" style units that do not use a pilot light which apparently are ABYC compliant if installed correctly with ventilation etc. From what I have heard these units do not use very much gas so I would say stick with the unit you have is gas usage is your only reason to change. The newer units I have heard incoporate more elaborate circuitry which may not be as well suited to a marine environment and these units in general scare me a little with the potential CO issues. They are also very expensive.

I am planning to install an Isotherm unit this winter that will use engine or 110volt to heat. Will probably go with the 6 gallon unit but maybe larger if I can find the room and $$.
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Old 30-06-2010, 12:52   #8
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we cruised with a 6 gallon on both boats for a lot of years and never ran out, but that is for two of us. The size of the crew might make a difference. This is our current set up,
http://tinyurl.com/yjfjt8x
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Old 30-06-2010, 15:27   #9
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We have 50 liters on our boat, and never want for hot water. Four or five people on board all taking hot showers in the morning don't exhaust it.

Proper marine calorifiers heat the water to a much higher temperature than domestic hot water heaters, and mix it with cold water at the tank to bring it down to less dangerous temp. So the relatively small volume (14 gallons or so) seems like much more.
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