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Old 29-09-2010, 04:31   #16
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Originally Posted by Jim Cate View Post
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

Jim,

I'm a licensed plumber/gas-fitter. The reason that a gas range is considered "safe" in comparison is that the relatively small burners on the range (less than 5,000 to 10,000 BTU's) burn highly efficiently - somewhere around 95% to 97%. There is less oxygen depletion and less CO produced. Plus - as someone (Gord?) mentioned, most people usually have fans running and/or ports/hatches open when cooking just because of the heat generated.

These tankless water heaters are typically in the range of 100,000 to 200,000 BTU's and burn somewhere in the neighborhood of 87% efficiency. That can fill a small space with CO awfully quickly.

Some companies also make units that can be mounted outdoors - not that you'd want to on your boat, but I'm thinking in terms of having a unit that might stand up to a damp marine environment a little better. Some manufacturers I know of, and have installed (in homes): Rinnai, Bosch, Takagi, Noritz - they've all been pretty good...no complaints or callbacks on any of them.
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Old 29-09-2010, 12:53   #17
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Still waiting to hear the logic behind the ABYC pilot light issue myself, I see no difference between an oven with a thermostat/thermocouple that gets left on for hours to bake. The oven burner kicks on brings the temp back up to the requested setting then shuts off. On, off, on, off all day long while baking. If no flame is present the thermocouple shuts off the gas. Same as on my hotwater heater. Why does ABYC like my oven but not my water heater?

Do these things really put out 100-200k BTU? Wow. This one I believe meets the ABYC requirements and is only 55k BTU. Precision Temp Boat Tankless Hot Water Heater. Gas Marine Water Heaters. Propane Boat Hot Water Heater

and its $1500. Like I said earlier I think you will be hard pressed to find one that meets ABYC for a few hundred bucks.
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Old 29-09-2010, 16:08   #18
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I can't really speak to the ABYC, since my boating experience is limited, and I'm really drawing on my practical experience in residential construction. As was stated earlier, I really think much of it has to do with the fact that - and correct me if I'm wrong - even if you're cooking in the dead of winter, you're likely to have hatches open simply because of the intense heat that would build up in the cabin. With a water heater, most of that unwanted heat goes out the flue. So not only are you burning more gas less efficiently with the water heater, you're doing it in a closed/unventilated space.

As someone else mentioned earlier, sealed-combustion, direct-vent units are the way to go. Again...in residential construction, my state (Massachusetts) gas code dictates a minimum of 4 feet clearance for the vent terminal to any windows (ports) or doors (hatches) on a non-direct vent appliance - good luck getting that on a boat! Direct-vent vent terminations can be as close as 1 foot. This is probably another reason the older models w/standing pilot are verboten.

We also have a section that says "Gas utilization equipment shall not be installed so its combustion ventilation and dilution air are obtained only from a bathroom or bedroom unless the bathroom or bedroom has [adequate volume according to another section of the code]". A direct-vent unit negates all that since it draws its combustion, ventilation and dilution air from outside the room.
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Old 29-09-2010, 16:38   #19
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Death and hot water...

This is not really boat related but in my youth we rented a big old Victorian house with a huge ancient instant hot water unit.

There was a minor problem with it and the agent sent round an old plumber.

I can still see him sitting on the bath with it running explaining very gently that it was producing enough CO to easily kill me.

The previous owner of the house was an old lady who had died slowly over a number of years (she left behind the weighing machine tickets to keep us cheerful).
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Old 29-09-2010, 17:13   #20
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This is what we use:
1.6 gpm LPG VENT FREE tankless gas water heater

If you go this way, get the one with the battery for the ignition not the turbine(high maintenance).
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Old 29-09-2010, 18:15   #21
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Quote:
Originally Posted by Ishmael View Post
Jim,

I'm a licensed plumber/gas-fitter. The reason that a gas range is considered "safe" in comparison is that the relatively small burners on the range (less than 5,000 to 10,000 BTU's) burn highly efficiently - somewhere around 95% to 97%. There is less oxygen depletion and less CO produced. Plus - as someone (Gord?) mentioned, most people usually have fans running and/or ports/hatches open when cooking just because of the heat generated.

These tankless water heaters are typically in the range of 100,000 to 200,000 BTU's and burn somewhere in the neighborhood of 87% efficiency. That can fill a small space with CO awfully quickly.

Some companies also make units that can be mounted outdoors - not that you'd want to on your boat, but I'm thinking in terms of having a unit that might stand up to a damp marine environment a little better. Some manufacturers I know of, and have installed (in homes): Rinnai, Bosch, Takagi, Noritz - they've all been pretty good...no complaints or callbacks on any of them.
G'DAy Ishmael,

Thanks for trying to introduce some data into this discussion.

I had a look at the specs for my Paloma gas water heater, and found that its burner is rated at 38,100 BTU/Hr on LPG. My Mariner LPG stove does not bother to include such data, but the physical dimensions and number of jets in the oven burner appear to be roughly half that of the Paloma, for whatever that's worth. The oven vents directly into the galley, while the Paloma has a 4 inch stack, about a foot long, that vents on deck. To me, that seems to offer less of a hazard than the oven.

The arguments about having ports open, etc are specious... when making a safety analysis one can't postulate such things. When in Tasmania, we often use the oven without opening any ports... enjoying the extra warmth! However, few yachts are very air-tight even "closed up".

And I again point out that while the oven is used for long periods, the Paloma is used for showers, and they are of short duration.

And, while I don't dispute your expert knowledge, why should stove burners be so much more efficient than water heater burners? And what does this "efficiency" really mean?

Lastly, this non-marine device is now around 15 years old and shows little degredation in appearance... can't speak to its efficiency, but the shower is still hot!

Anyway, I'm not advocating that anyone else use such a device, but I am not convinced that either CO or oxygen depletion are serious hazards in an installation like ours.

YMMV.

Cheers, and thanks again.

Jim and Ann s.v Insatiable II lying Michaelmas Cay, Qld, Oz
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Old 29-09-2010, 18:35   #22
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Ours is an older Bosch ventless heater. It has an ODS (Oxygen Depletion Sensor) shut off if the supply if the CO rises too high. You could add a detector if you want to be sure. The unit sits inside the shower. I always crack open the port in the head when we use it. It's 19 years old and seems to work fine. The waste heat does a nice job drying out the shower. I also have a solar vent in the head too. Dealing with the vent or the waste heat and CO is the issue you need to address some how. It is nice to be 2 days on the hook and able to make hot water. We don't have a large water tank so it seems to work fine. After two days I need the engine run and so it fills the gap nice. I don't have a hot water tank and the Bosch takes less room than a hot water tank. Hot water tanks with shore power heat cost more for 7 gallons.

I light the pilot each time we use it and shut it off when we don't I really don't see the need to have the pilot always lit. The three stage interlock will kill the main if the pilot goes out. It has a sparker built in to make it easy for even the Admiral to light it. There is also a flow rate so you can have deadly hot or just pretty hot water coming out. Extra hot for dishes and low for showers.
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Old 29-09-2010, 19:26   #23
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We rebuilt tankless water heaters for recirculating applications and use them in our floating hot tubs. You can purchase tankless water heaters with heating capacities from 25,000 BTU's on up. Many of the less expensive ones use two 1.5 volt batteries, and have an automatic piezoelectric ignition switch that is turned on with a pressure switch.
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Old 29-09-2010, 20:14   #24
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Originally Posted by Jim Cate View Post
G'DAy Ishmael,

Thanks for trying to introduce some data into this discussion.

I had a look at the specs for my Paloma gas water heater, and found that its burner is rated at 38,100 BTU/Hr on LPG. My Mariner LPG stove does not bother to include such data, but the physical dimensions and number of jets in the oven burner appear to be roughly half that of the Paloma, for whatever that's worth. The oven vents directly into the galley, while the Paloma has a 4 inch stack, about a foot long, that vents on deck. To me, that seems to offer less of a hazard than the oven.

The arguments about having ports open, etc are specious... when making a safety analysis one can't postulate such things. When in Tasmania, we often use the oven without opening any ports... enjoying the extra warmth! However, few yachts are very air-tight even "closed up".

And I again point out that while the oven is used for long periods, the Paloma is used for showers, and they are of short duration.

And, while I don't dispute your expert knowledge, why should stove burners be so much more efficient than water heater burners? And what does this "efficiency" really mean?

Lastly, this non-marine device is now around 15 years old and shows little degredation in appearance... can't speak to its efficiency, but the shower is still hot!

Anyway, I'm not advocating that anyone else use such a device, but I am not convinced that either CO or oxygen depletion are serious hazards in an installation like ours.

YMMV.

Cheers, and thanks again.

Jim and Ann s.v Insatiable II lying Michaelmas Cay, Qld, Oz

Yep...whether it's state/national gas codes or ABYC standards, bureaucracies like to state the rules but fail to explain the rationale behind them. And trying to figure it out is often a frustrating exercise in futility.
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Old 03-10-2010, 07:48   #25
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... I had a look at the specs for my Paloma gas water heater, and found that its burner is rated at 38,100 BTU/Hr on LPG. My Mariner LPG stove does not bother to include such data, but the physical dimensions and number of jets in the oven burner appear to be roughly half that of the Paloma, for whatever that's worth ...

FWIW: Typical propane Bar-B-Q burners are usually rated 10,000 BTU/H each. I wouldn't expect stove tops to vary hugely.
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Old 03-10-2010, 10:44   #26
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Gas (propane or otherwise) stove burners commonly range from 5-12,000 BTU and anything rated 10,000 or higher is considered top quality. Expect 6-8,000 from "commodity" brands.

So if a flash water heater is putting out 40,000 BTU...and Bosch makes them near 200,000 BTU capacity to feed two bathrooms at once...

A little quick math says the 40,000 btu heater is putting out 8x as much CO as one cheap stove burner. That will elevate your blood level of CO by 8X and even though you are just using it for a short time, once CO binds to the hemoglobin in the blood it tends to stay there and get out very very slowly. I would expect this means the shorter exposure at higher levels has to be treated as "higher levels period" without much regard for the exposure time.

In the case of a 100,000 btu heater versus a single good stove burner, that's still 10X the exposure and possibly 20x-40x (comparing a 5kbtu burner to a 200kbtu heater).

When you've got fast and loose--but accurate--numbers like that to throw around, there's real risk of someone getting killed. As my friend in the shower found out.

And let's not forget,stoves and bbqs and simple heaters CAN AND DO kill people from CO poisoning every year, even in homes. CO detectors are being required for home installations because of that very problem.

Don't want to buy one? Don't want to worry about it? That's fine with me, I believe in freedom of choice. And good ventilation.
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Old 03-10-2010, 10:49   #27
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Gas (propane or otherwise) stove burners commonly range from 5-12,000 BTU and anything rated 10,000 or higher is considered top quality. Expect 6-8,000 from "commodity" brands...
Thanks for the accurate details!
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Old 08-10-2010, 09:40   #28
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Doug,

Tankless water heaters have been the standard across Europe for decades. I beleive the danger to which several readers refer, is correct - the old fashioned pilot light could blow out and the gas would continue to flow into the room. Today's units have reduced the danger by introducing electronic fail-safes which switch the unit off if the pilot goes out, or when a reduced level of oxygen is detected.

I bought a marine certified CNG unit 20 years ago - the price was outrageous, but it had all the fail-safe electronics, and still is working perfectly. Today I am about to purchase a replacement unit with more flow - but it won't be marine certified (yes - I know that in terms of insurance it is a risk). My decision is strictly price related. I recently mentioned to a friend who is an engineer/manufacturer of one of the major brands in Europe : Hey I see you are now exporting your units to the States, for the marine industry. They are very expensive there. Are they different from the units used for domestic usage ? The answer was similar to Beau's story, above. - the difference is the certification cost, everything else being the same.

Having said all this, you should keep safety in mind - proper venting (even if the unit does not require venting), electric solenoid cut-off, manual cut-off valve, and electric breaker to control on/off.
I keep my unit below decks at the stern, vented to the exterior, mushroom cap vent cover.

Good luck.
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Old 08-10-2010, 15:05   #29
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I believe the danger to which several readers refer, is correct - the old fashioned pilot light could blow out and the gas would continue to flow into the room.
We are talking seriously olden days for this feature. I doubt many members were alive before the thermocouple pilot light became standard on high capacity burners.

It's the source of oxygen that you need to be mindful of. They have not found a way to get around that nor can crew survive long without Oxygen.

There is some degree of Carbon Monoxide danger in any combustion process. The calibration of the burner and the venting will make sure it's safe. You can always add a CO detector. On any boat one of these is a good idea. I found an exhaust leak from the engine from mine. I don't think I would have found it as soon without the detector. They are just too cheap not to have one or more aboard.
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Old 08-10-2010, 16:00   #30
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Paul's note to safety hits the mark.
I installed my unit in the lazarette because I wanted it to be isolated from the living area of the boat, for all the safety reasons Paul raises.
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