On demand hot water?

The co generation concept , the engine or noisemaker is on for its purpose , so capturing waste heat is a no brainier for efficiency.

The danger to the engine is very minor , I have never seen or heard of it happening in 55 years , so far.

The DANGER of a leak of the engine coolant into the fresh water , which could poison the FW does in theory exist.

The solution is a double wall heating element , common in house alt energy setups , probably too expensive for most boaters.

Simple , if you TASTE anti-freez , dont drink the water.

WesK said:

That water heater needs a lot of electrical power. You would need a bilge full of batteries and a humongous inverter to power it and the engine's alternator would take many hours to recharge the batteries. It's simply not practical on most boats unless you have a genset.

There is nothing wrong with heating water using engine coolant and it's "free".

Look around at other boats, especially production boats. These people have figured out what works and what doesn't. They have already considered what you are proposing and figured out that it's not the best solution.

Click to expand...

to reiterate, in your case it's all about the Inverter, as no many how batteries you have, the Inverter will have to transform that power.

Also, having lived in Germany with an on demand water heater for 4 years, it would be about my last solution, but never on a boat in any case.

My Marine water heater will keep the water hot for more than a day, even turned off.

Good question though.

MC Escher, I don't know why you took my post as being hostile. You posted your opinion, I posted mine. I don't think it is "physics", it's opinion. I stand by mine.

My Marine water heater will keep the water hot for more than a day, even turned off.

The Rheem claims to loose 5 deg per 24 hours , starting with the usual 180F coolant heated water it should be good until its slowly filled with cold water from use.

The Takagi TK3 on-demand water heater is quite efficient . It is rated at 3 amps. Therefore you would Not need a " bilge full of batteries" to operate it, as WesK thinks in post #11.

My old Irish grandfather always told me it's best to know what one is talking about before going off half cocked.

BobH, in post #14, Sorry about your luck with your propane water heater.

Did you install it yourself? or did you have a Professional install it?

Wxx3 said:

to reiterate, in your case it's all about the Inverter, as no many how batteries you have, the Inverter will have to transform that power.

Also, having lived in Germany with an on demand water heater for 4 years, it would be about my last solution, but never on a boat in any case.

My Marine water heater will keep the water hot for more than a day, even turned off.

Good question though.

Click to expand...

Mr. Wxx, could you elaborate on why? I've never used the on demand except for a very small and cheep unit that was electric and mounted under the sink. I wasn't very impressed with the output but I assumed a gas whole house unit would have the kinks worked out. I can assume things all day but I sure don't want to install something that is going to have to be pulled out after a couple of uses...

FF said:

The DANGER of a leak of the engine coolant into the fresh water , which could poison the FW does in theory exist.

Click to expand...

Pretty slim chance considering the potable water pressure is generally around 2 to 3 times the maximum engine coolant pressure.

Just an aside, but maybe a cheap fix for your overheating concerns.
Why not install an alarm? When the engine heat reaches a certain point, the alarm sounds. You shut her down to find the problem?
Free hot water and peace of mind all at the same time

I'm one of those anti-propane types.
My home grill is charcoal, my house runs off of electricity.

Personally, I don't want much more than the little bottle one uses for the rod holder mounted grill, on board my boat. Just my personal paranoia

OD

Capt Nemo said:

The Takagi TK3 on-demand water heater is quite efficient . It is rated at 3 amps. Therefore you would Not need a " bilge full of batteries" to operate it, as WesK thinks in post #11.

My old Irish grandfather always told me it's best to know what one is talking about before going off half cocked.

Click to expand...

Seriously, 3 amps? Post a link.

And take a nice pill first.

WesK said:

Seriously, 3 amps? Post a link.

And take a nice pill first.

Click to expand...

Ask and ye shall receive:

http://www.takagi.com/download/product_manuals/T-K3.pdf

Another consideration is failure based on complexity. While I have never dissected an on demand hot water heater, clearly there is some complexity (read potential failure points) with a control system that senses water flow or temperature drop, maintains a standing pilot light or has electronic ignition, and an automatic burner control. As already mentioned, none of these units are constructed for the corrosive marine environment. The 20+ gallon HW heater on my boat has a tube (heat exchanger) that goes in and out of the side of the tank. Pretty low on the complexity failure point scale. I'm considering a 2 heat exchanger unit when it comes time to replace this one. Would like to use the free waste heat to make HW twice a day when I run the generator to charge the batteries and take care of the heavy amp 120 ac chores (like cooking).

Ted

3 amp circuit protection...but I didn't see a duty cycle....

of course it's a LP/Nat Gas heaters so I think there's a few apples and oranges in the "3 amp" war.....

Wxx3 said:

Also, having lived in Germany with an on demand water heater for 4 years, it would be about my last solution, but never on a boat in any case.

Click to expand...

I live part time in Thailand, and our 2 units work flawlessly.

Of course I'm always amazed that I failed to convince my Thai wife to mount the water tank up higher than ground level (like on the second floor), and OUT IN THE SUN (metal tank)...free hot water.

Anybody who installed that Takagi on a boat would soon throw it overboard. Most of your generators are quieter than that thing. 3/4" gas hose on your boat? 4" exhaust vents? Really??

Sorry, just reading the manual... And have installed dozens of them.

Capt Nemo said:

BobH, in post #14, Sorry about your luck with your propane water heater.

Did you install it yourself? or did you have a Professional install it?

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Not sure I understand the question. You hook up the propane and water lines, what more could a professional do? The boat originally came with a propane on demand water heater which the PO had discarded. After I installed another one I understood why.

Bob

I wonder why the love/hate relationship with them? Some swear by them and others not...is it install issues? If you meet the install specs can you expect the same performance so personal preference is just that?

Off Duty said:

Ask and ye shall receive:

http://www.takagi.com/download/product_manuals/T-K3.pdf

Click to expand...

Thar's a gas water heater, not electric so the 3 amps is only for the controls and such. It's not making hot water with electricity so your clain of efficiency is not valid.

It's going to be pretty difficult to operate a gas water heter on a boat.

The Precision Temp ShowerMate propane marine water heater with patented VariFlame controls delivers an endless flow of hot water for the ultimate shower. It is perfect for boaters who don't want to leave the comforts of home behind while on the high seas.

It’s lightweight, compact, efficient and installs almost anywhere. In fact, the typical boat owner can expect to use very little propane for all this comfort; estimated 920 gallons of shower temperature water* per 20 pounds of propane.


Precision Temp Boat Tankless Hot Water Heater. Gas Marine Water Heaters. Propane Boat Hot Water Heater

If it really varies the flame then that may be a way to go. The one we had only had on and off so if the shower was too hot and you turned the hot water down, the flame would shot off and then you would get cold water.

Bob

psneeld said:

The Precision Temp ShowerMate propane marine water heater with patented VariFlame controls delivers an endless flow of hot water for the ultimate shower. It is perfect for boaters who don't want to leave the comforts of home behind while on the high seas.

It’s lightweight, compact, efficient and installs almost anywhere. In fact, the typical boat owner can expect to use very little propane for all this comfort; estimated 920 gallons of shower temperature water* per 20 pounds of propane.


Precision Temp Boat Tankless Hot Water Heater. Gas Marine Water Heaters. Propane Boat Hot Water Heater

Click to expand...

Hmm......


[FONT=arial,helvetica,verdana]"Mounting flanges included. Must be mounted in accordance with any applicable Coast Guard and ABYC recommendations.[/FONT]"


Short of mounting it on the deck or on top of the house, it would be interesting to see what you would have to do as far as installation to meet those standards and satisfy an insurance underwriter.

Ted

O C Diver said:

Hmm......


[FONT=arial,helvetica,verdana]"Mounting flanges included. Must be mounted in accordance with any applicable Coast Guard and ABYC recommendations.[/FONT]"


Short of mounting it on the deck or on top of the house, it would be interesting to see what you would have to do as far as installation to meet those standards and satisfy an insurance underwriter.

Ted

Click to expand...

Not sure why...other than recommendations for hoses and shutoff...propane isn't all that complicated if everything is outside but the device.

Mainly posted to show there are propane devices sold for boats as well as numerous installs by others of non-marine tankless heaters. Can't remember which brand of sailboat but one was offering I think Poloma ones for awhile.

psneeld said:

Not sure why...other than recommendations for hoses and shutoff...propane isn't all that complicated if everything is outside but the device.

Click to expand...

My understanding (I could be wrong) was that propane appliances such as refrigerators, required sealed combustion chambers with intake and exhaust gas plumbed to outside the boat to meet code and insurance requirements. This unit didn't look to be so equipped. Maybe if you are going to plumb a fuel shutoff valve at the propane tank and turn it on and off each time you use it (like a stove), those requirements might not apply. Probably not going to be able to mount it below deck (engine room) to your insurance companies satisfaction.

Ted

WesK said:

Thar's a gas water heater, not electric so the 3 amps is only for the controls and such. It's not making hot water with electricity so your clain of efficiency is not valid.

It's going to be pretty difficult to operate a gas water heter on a boat.

Click to expand...

Do you always have to be so damned argumentative? You asked for a LINK, not a recommendation

Personally, I wouldn't have it on a boat of mine either, but that's just me and my preferences.

I gave you what you asked for. Draw your own conclusions.

OD

O C Diver said:

My understanding (I could be wrong) was that propane appliances such as refrigerators, required sealed combustion chambers with intake and exhaust gas plumbed to outside the boat to meet code and insurance requirements. This unit didn't look to be so equipped. Maybe if you are going to plumb a fuel shutoff valve at the propane tank and turn it on and off each time you use it (like a stove), those requirements might not apply. Probably not going to be able to mount it below deck (engine room) to your insurance companies satisfaction.

Ted

Click to expand...

Read through the install manual...didn't seem complicated yet "must be installed in a vented compartment"....well technically that's the engine room on most boats...so I'm not sure and would have to make a few calls.

Also with you on the "can you hook a shutoff solenoid up to the electrical system of the heater?" if not...then I would guess you would have to do it like a stove (what a PIA if that was the only source of hot water....you would need a shutoff at every sink too).

I think if I did one...and at $1500 I doubt it for my size boat...I would do one to feed my hot water tank..that way I could turn it on/off just for the big water uses but not for the hand washing, etc....maybe...I'd really have to think about it as tank hot water heaters seem just fine.

Off duty...

O C Diver said:

Hmm......
[FONT=arial,helvetica,verdana]"Mounting flanges included. Must be mounted in accordance with any applicable Coast Guard and ABYC recommendations.[/FONT]"

Click to expand...

I have never seen an LPG on demand water heater that could be mounted inside a boat and comply with both it's own installation instructions and ABYC.

Finally a topic I am actually an expert on. I have installed and repaired most brands of tankless water heaters out there. I know their strenghts and their weaknesses. I do not believe marine use is a good application for them at this time. Choosing a proper installation method would be critical.
There are a lot of issues to consider when installing a tankless. The first of which is that most if not all portable propane tanks are not rated to deliver that much fuel and the valves and regulators could freeze from the cooling effect of the LP expansion. At a minimum freezing would stop gas flow altogether. Worst case, it would crack the valve or cause a fitting to leak.
Another factor to consider is most tankless units require a minimum of 35-45 psi to operate correctly. If they do not have this water pressure, the water can boil before it leaves the heat exchanger (PV=NRT), resulting in some sort of damage to the heat exchanger and lots of disconcerting noises coming from it.
Another issue is condensation. A condensing unit will need to have its condensation drained somewhere. Non condensing units are not quite as efficient and have copper heat exchangers. These might be susceptable to corrosion from salt air corrosion. If salt water ever got into your intake or exhaust, good luck as corrosion happens quickly! Condensing units are probably the best option as they have both combustion and exhaust venting made of PVC. The venting material will be 3" PVC at a minimum.
Both condensing and non condensing units have a lot of electronics in them along with motorized valves. Repairs to these units, some more than others, are a painful process of locating repair parts. Warranty service for these units can be frustrating, even for a professional. Some companies are better than others. Some dont really have any after purchase support.
Another thing to consider is that most units will require a dedicated 3/4" gas line from the tank to the unit. Larger if the tank and water heater are farther away.
If anyone has any specific questions I can try to answer them here. If you have a lot of questions, send me a PM and I'll send you my telephone number.
If I had to choose one unit (today) to use in a marine environment it would be an Eternal Hybrid water heater. The make a smaller unit about 100,000 BTU that should match water demand on a boat nicely and they have a minimal amount of parts and wiring in them and they actually have enough room in them to get your hands in and work on if you have to. Most of the unit is made of stainless steel, including the cabinet. It has an integral tank that holds about 2 gallons of water in it. When the unit is switched on , it will keep this water hot at all times.
regards,
Scott

Scott,
I'm assuming you have knowledge of both electric ones as well as propane ones?

I seem to remember a posting on this forum (likely another subject thread) that indicated there were a few electric units that might work OK off of inverter power??

brian eiland said:

Scott,
I'm assuming you have knowledge of both electric ones as well as propane ones?

I seem to remember a posting on this forum (likely another subject thread) that indicated there were a few electric units that might work OK off of inverter power??

Click to expand...

Yes there are ones that would work fine assuming your inverter could put out 80-120 AMPs. Seriously, electric 'whole house' tankless are not really worthy of consideration even for your house as most homes would require their electrical service and panel to be upgraded to feed the $700 water heater.

Here is an example that will put out about 3-4 gallons/min

http://s3.pexsupply.com/product_files/EX280T2T-brochure.pdf

bligh said:

Yes there are ones that would work fine assuming your inverter could put out 80-120 AMPs

Click to expand...

Wow,at what voltage is that AMP figure?

Seriously, electric 'whole house' tankless are not really worthy of consideration even for your house as most homes would require their electrical service and panel to be upgraded to feed the $700 water heater.

Click to expand...

Wow, are they that costly? Sure a lot cheaper here in Thailand

And here they work off of 220v, so less amps I'm sure.

Don't most homes have 220V for electric ranges and washer/dryers? Couldn't that 220v supply be fed to the tankless waterheater?

Correct me where I'm wrong, but aren't 2 of the biggest energy consumers in one's home the refrigerator and water heater?...and both are not very well insulated, so that contributes to their loses??