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Old 05-06-2011, 08:03   #1
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On Demand Hot Water - Gas or Diesel

Hello,
My wife and I are new to cruising and have just purchased a 45 foot catamaran. It only has water heating from running the engine. We will be living on board for a while and would appreciate the recommendations of other liveaboard cruisers in regard to on demand hot water systems.
We are familiar with the Gas unit that was on a Seawind 1000XL that we had. This seemed to work well. I have seen some diesel units advertised.

Which would you recommend with regard to:
safety
reliability
running cost
purchase cost
installation cost
delay time before the water is hot for shower or galley sink.

Some many criterial! Sorry it is the engineer in me leaking out. If we add this unit, we may as well do it right the first time.


Great forums, I think we need to add a couple of extra solar panels to power the laptop, so we can read all the fantastic information in this forum.
Thanks in advance.
Ian
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Old 06-06-2011, 07:00   #2
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Re: On Demand Hot water - Gas or Diesel

First of all, welcome to the forum kiwi-ian. I have a Rinnai (ph.) on-demand propane water heater (in addition to the standard heat exchanger unit) and it works perfectly. Indeed, mine is the original from 1994 so I think that speaks to reliability/durability.

I have no experience with diesel on-demand water heaters, but a few thoughts come to mind:

1. Diesel burns at a lower temperature than propane, so I suspect it would be less efficient.
2. Having had a diesel stove on a previous boat (and having replaced it with propane). they do tend to produce some soot.
3. Diesel stove burners needed to be pre-heated with alcohol - I am again unsure what they have done with the water heaters, but wonder if they must be left on once up an running.
4. Diesel fuel does produce an odour and it can be problematic if there area any spills .
5. I know some will express concern about propane leaks, but really, it is no different than a propane stove. I would have copper tubing installed at the time of manufacture (as on my boat) with a gas sniffer and then wouldn't worry about it.
6. The diesel units will obviously require a pump to run the fuel up to the heater; apart from being something else to go wrong, I wonder about air locks. Lets face it, bleeding a diesel engine is no fun and I suspect that, depending upon where the unit is mounted, the results of the inevitable spills will be much worse.

Anyway, just some thoughts. Llet us know what you decide.

Cheers!

Brad
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Old 06-06-2011, 07:23   #3
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Re: On Demand Hot water - Gas or Diesel

Small on demand hotwater heaters require a few seconds warm up time, EVERY time you turn them on. Then they only maintain a steady temperature if you leave the water on. They are NOT appropriate to saving water by getting wet, turning it off, soaping up, and then rinsing. I don't consider them a good cruising alternative.

For marinas, you could have a very small, (5 gal) standard home unit. Then, when cruising, use a solar heated, 2.5 gallon black plastic garden sprayer with a thumb actuated dish washing nozzel on the hose. We get two nice showers with ours, including washing hair. It really limits water waste.

In moderate climates, we let it sit in the sun a few hours in the afternoon, and this provides shower water at a perfect temperature around sundown. In cooler climates or cloudy days, we spray a tea kettle full and heat it on the stove until it almost whistles.

After poring it back in the sprayer, it is the perfect ratio of hot to cold to make a nice warm shower.

We shower in the cockpit, and this keeps the residual moisture out from down below, where we don't want it.

It is simple, cheep, last decades, and a really nice shower...

M.

BTW, We can collect rainwater in the dinghy, jug it, and later use THAT water in the sprayer for showers, or otherwise washing clothes. This would be water that is OK for this, but you would not want in your tanks.
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Old 06-06-2011, 07:26   #4
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Re: On Demand Hot water - Gas or Diesel

I would personaly favour the diesel system for a few reasons.

Diesel will be more universally available.
Diesel is safer than gas
a Diesel system is easier to understand and service for a layperson
Its likely you will already have a diesel tank aboard so storeage is more efficient, ie, one fuel for 2 uses.
An Eberspacher water heater will fire up from cold and doesnt need preheating
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Old 06-06-2011, 07:39   #5
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Re: On Demand Hot water - Gas or Diesel

I have just installed an ITR Hurricane combination water heater/hydronic system. Only been in 2 days - still evaluating...
Depending on your needs I would say diesel can, and is carried in greater quantities and easier refills than propane refills.
But you need to evaluate fuel consumption...
Diesel is used in most/many New York heating systems(it gets cold here).
Many are upgraded to propane. Propane is definitely an easier, cleaner system and is then piped in and cheaper than "trucked" in diesel to tanks.
But I think this is the opposite on a boat. And "we" need to know how to maintain and repair diesel systems...

n.b. I use "propane" as the generic term for "gas" (not petroleum)...
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Old 06-06-2011, 07:53   #6
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Re: On Demand Hot water - Gas or Diesel

I am assuming that he will be fitting a propane stove and hence, there would be no need for a separate fuel system; if he has concerns about the availability of propane, then he had better also specify a diesel stove. Regarding servicing, I say, my 16 year old Rinnai heater has never needed servicing so I suspect that if and when it fails, it would be easy (and cheap) to simply buy and install a replacement unit.

Mark of course is right - the water is only hot after running for a few seconds; mind you, the same is true of water from any water heater as there is a run of pipe or hose from the heater to the outlet (and often further than from an on-demand heater, that really should be installed very close to the outlets).

Mine is plumbed into only the galley sink and an essentially adjoining shower compartment; I do not expect it to heat water in the other hull.

Brad
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Old 06-06-2011, 08:03   #7
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Re: On Demand Hot water - Gas or Diesel

diesel actually gives you more BTUs than propane, gallon for gallon about twice as much.
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Old 06-06-2011, 13:54   #8
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You might also look into the Whisper Generator that will heat water when it generates electricity.
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Old 06-06-2011, 14:11   #9
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I've had great service out of a Rinnai gas (I think called propane in other places) heater. If you're using gas for cooking there is no downside to using it for heating water. I believe that the greatest risk for gas is on monohulls that have a gimbaled stove and therefore require highly flexible piping. On a Cat you don't need flexible piping for the stove and neither types need it for the water heater. The closer you have the water heater to where you use the hot water the less you'll waste.
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Old 11-06-2011, 23:44   #10
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Re: On Demand Hot water - Gas or Diesel

Wow! Thanks for all the great responses. I have learnt a lot, and been encouraged by the great support provided, especially to someone new to cruising. What a great community. Regards Ian
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Old 12-06-2011, 01:38   #11
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Quote:
Originally Posted by Safari38LH
You might also look into the Whisper Generator that will heat water when it generates electricity.
Not made anymore since the factory was demolished in the recent NZ earthquake.

I have ebespacher diesel heating , it works well, it takes about 30 minutes to get hot water. It's not a system you would install just for water, more a complete boat heating system.

If you are liveaboard surely you have shorepower, why not use it.

Dave
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Old 16-06-2011, 02:40   #12
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Re: On Demand Hot water - Gas or Diesel

I just joined, but my project is a still-in-progress houseboat. Check out the pics: Pictures by projecthouseboat - Photobucket
I just did a search on propane hot water heaters which has been occupying my thoughts for some time now. My idea is this: http://i1216.photobucket.com/albums/...t/f557792d.jpg Note that the water heater/burner is to OUTSIDE of the superstructure--just outside from the shower area...such a short distance from burner to shower head should give a short water heat up time...right?
Aside from all the other protections (cut-off selenoid co sensor etc) a future surveyor
remark could be how any fumes could waft into the cabin like in this rendering:
http://i1216.photobucket.com/albums/...t/99d98a56.jpg
Other forums are downplaying this idea, but I haven't ruled it out yet...what do you think?
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