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Old 21-09-2010, 13:01   #1
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Instant Gas Water Heaters

I have read some previous threads about heating water aboard and am wondering if there are any new opinions on the heating of water, always on the hook, primarily for showers.
Danger of explosion and water preservation are always issues but I have had a gas stove for decades aboard and have learned to respect it and be careful.
I have seen instant gas heating units online from $199 to $1500 that sound good.
I would rather not spend $1500 but don't want a piece of junk. I do know you get what you pay for, within reason.
Any opinions?
Thanks.
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Old 21-09-2010, 13:46   #2
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Doug, I have a Rinnai on-demand water heater fitted to my cat and have found it be both reliable and efficient. As I understand it, they were fitted to many British boats built in the 90's (mind dates back to 1994) and, unlike my 120Volt/heat exchanger tank unit, it has never required a replacement.

I have seen comparable units at fairly low prices and, while I cannot speak to any of those products, I can note that even the Rinnai does not seem to have been boat specific; certainly, the wall-mount brackets and other hardware are not stainless steel. Regardless, it provides a virtually instant supply (steady after a few seconds) of hot water limited only by one's tankage. The fact that it uses propane is particularly useful underway/at anchor, where the need for 120 volt electricity/heated water from the diesels makes my tank unit rather impractical. For what it is worth, my one propane unit heats water for both the galley sink and a shower that is located about 8 feet away (albeit not the heads in the other hull).

So long as you have ventilation on the cabin roof above where it is mounted and use the same precautions as with any propane stove, it should cause you no problems.

Brad
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Old 21-09-2010, 13:46   #3
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Doug, you might want to specify which gas you're planning to use. I had one on a previous boat that was powered by CNG. Worked great, and yet I would never again have a CNG boat because of the difficulty procuring fuel.
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Old 21-09-2010, 14:38   #4
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Doug I have a CNG fired unit in my boat now but it is not connected as insurance company required it to be removed for non compliance with ABYC. I have looked into this subject some and have found a few things. First off the units that are ABYC compliant are not cheap, prices start around $1000. They cannot operate with with a pilot light so the entire burner must be controlled by a pressure switch that turns on the gas and lights it. This means somewhat more complex circuitry which isnt always the best in a marine environment. Then there are all the precautions that must be taken with the exhaust. Its NOT the same as your stove, its more like adding a cabin heater with fresh air vents and chimmneys etc. More holes in the boat and more opportunity for CO issues. Not impossible to deal with just more work.
One other thing. The instant heat unit in my boat was set up with an exhaust fan to assist in removing the combustion exhaust. This thing is basically a blower fan. Its loud. Maybe not all the new units are loud but its a consideration for sure. Something to ask about.


All in all I am still very find of the concept but in order to do it right it will cost significantly more than a conventional water heater that runs off the engine or AC power. I am opting most likely for an Isotherm conventional unit that will run off the engine or AC power and can also be set up to take excess power from a solar or wind genny and heat the water.
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Old 21-09-2010, 14:45   #5
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G'day, mate. We have an older LPG unit (not sure it is even manufactured any longer). We use it every other day when we don't have to run the genset to get hot water. They are commonly used by Kiwis down here on boats. A couple of hundred bucks equivalent U.S. buys a pretty decent one at the shops. Cheers.
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Old 22-09-2010, 06:03   #6
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Thanks for the responses and good information. I use propane as it is so available. In the head I have an existing overhead vent and an opening port and will try to find one without a standing pilot but with automatic ignition. There should be no trouble running feeding hot water to the galley as well.
Now to find some actual brand names that sailors have experience with.
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Old 22-09-2010, 10:24   #7
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Doug, when you look at flash heaters look at how they have to be vented and whether they have any CO or flame-out detection systems. A friend of mine was nearly killed in the early 90's when one of the early systems filled the head with CO and he passed out. Other crew started to wonder, why his shower was taking so long, and got him out in time.
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Old 22-09-2010, 12:48   #8
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Doug, when you look at flash heaters look at how they have to be vented ...
And choose Direct Vent, Sealed Combustion type.
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Old 22-09-2010, 16:59   #9
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G'Day all,

We've used a simple Paloma brand heater for years, one on each of our cruising boats. On I-2, it is located in the head compartment, and has a 4 inch stack running straight up through the deck to a mushroom vent. We also have a small muffin fan that blows air from the cabin into the head compartment whenever the shower pump is activated. Seems to work just fine for us.

Can someone explain to me why these systems are considered so dangerous? Their burners are similar to the oven burner in our stove, which is vented directly into the galley. I suspect that this is true on nearly every cruisingboat with LPG cooking. The oven is often on for hours, while the water heater runs for a few minutes at most.
I suppose that the relatively small volume of the shower/head compartment may be part of the picture, but is there something I'm missing?

Cheers,

Jim and Ann s/v Insatiable II lying Cairns, Qld, Oz
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Old 28-09-2010, 11:50   #10
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I was told by my surveyor that the unit I had and many of the older units use a pilot light and that was the big issue. I have never understood the logic of ABYC having a problem with the units myself especially when compared to using an oven with a thermocouple to regulate the oven temp. I see no difference. You light the pilot light, water pressure ignites the burner, you have hot water. When done you turn the water heater off like any other gas appliance. Thermocouple shuts off gas if there is no heat (ie pilot light when out).

Im certain more astute forum members can expound on the logic here.
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Old 28-09-2010, 12:27   #11
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I believe cooktops are intended to be attended whilst in use (ovens, perhaps not so much, in practice), whereas heaters (space or water) are intended to operate safely unattended.
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Old 28-09-2010, 13:43   #12
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Jim, maybe because a stove gives off so much more heat, there's an expectation that you'll have some ventilation or be paying some attention to it? As opposed to the flash heater being ignored in a small head compartment, while someone is getting lazy in warm water and high humidity. Better conditions to quietly pass out in?

Or maybe, stoves are being ignored because they were around so long before anyone bothered paying attention to CO poisoning?
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Old 28-09-2010, 21:58   #13
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I believe cooktops are intended to be attended whilst in use (ovens, perhaps not so much, in practice), whereas heaters (space or water) are intended to operate safely unattended.
G'DAy Gordy,

Ok, I can agree about the attendance issue, but how does that affect the CO hazard?

Our oven is often on for hours at a time. It's attended in the sense that we're on the boat, savouring the aromas of baking bread, but how does our presence remove the danger?

The water heater is only lit for those times we are showering. During the shower period, the burner is off more than it is on (water misers we are!). The pilot light has a thermcouple safety, which also disables the main burner should the pilot go out. I just don't see that it is a great hazard to our well being, but I'm willing to be educated.

Cheers,

Jim and Ann s/v Insatiable II lying Michaelmas Cay, Qld Oz
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Old 28-09-2010, 22:42   #14
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I have installed one in our boat without it being vented to the outside. I reasoned, as others have spoke to, that the emissions from the unit do not exceed my stove. I also have seen production boats with these installed with no outside ventilation. Most of what I have seen, they place the unit on a wall in the galley. Mine is in a cupboard. I have installed a short section of metal ducting to dissipate the heat only. I can hold my hand over the end of the ducting and experience no heat of consequence. My unit also has a safety for the pilot flame which shuts off after 20 minutes of no use. However, we use a solenoid at tank to shut off after use. Don't "T" into the main propane line with one shut off solenoid. Instead, "T" into the propane so that the unit has it's own solenoid. Otherwise, you might find the water heater "bleeds" the propane out of the stove line, which requires a few seconds or more for the stove to light.
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Old 28-09-2010, 23:49   #15
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I have had instant gas hot water heater on two boats, worked great. The first one used a pilot light and the latest one uses a small battery to light the gas when you turn on the hot water tap.

I bought mine on ebay for $200.00 but apparantly the gas industry in Australia is tightly controlled. When I got a licensed gas fitter to install it, he took one look at my ebay special and said "I can't install that, it is not Australian standard approved" I said what is wrong with it, he said "nothing, they work great" but the LAW says you must use an Australian approved one, there is only one brand available and it costs $1,000.

Anyway, after a carton of beer, he installed an attachment that could be used to supply gas to a barbecue or something else and when he was gone I could change it over. Australia????
I have it installed on the back deck and it is vented to the outside
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