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Old 02-15-2013, 07:32 PM   #1
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On demand water

Before I start I would like to preface that I know I could blow up using propane on the boat. Now, I would like to build an enclosure on my roof that would hold two 20# bottles and on the outside mount a 5gal/min on demand water heater. It will be on the roof that if the gas leaks it will go over the side. I would pipe down to the galley on the outside and stub into a stove. Maybe pipe down to the aft for a grill. The hot water would go down the wall and be distributed to a shower and sinks. Does anyone have any experience with doing this or experience at a dirt house on how much fuel will be used? Thanks Paul
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Old 02-15-2013, 07:47 PM   #2
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Before I start I would like to preface that I know I could blow up using propane on the boat. Now, I would like to build an enclosure on my roof that would hold two 20# bottles and on the outside mount a 5gal/min on demand water heater. It will be on the roof that if the gas leaks it will go over the side. I would pipe down to the galley on the outside and stub into a stove. Maybe pipe down to the aft for a grill. The hot water would go down the wall and be distributed to a shower and sinks. Does anyone have any experience with doing this or experience at a dirt house on how much fuel will be used? Thanks Paul
Wouldn't the documentation on the water heater tell you how much fuel it would use?

Of course, fuel use depends on how much water you want to heat and from what low temperature to what hot temperature.
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Old 02-15-2013, 07:53 PM   #3
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Condensing Tankless - Water Heaters Residential by A. O. Smith

Something like this will give you good service life without blowing up your boat

Plumb it by "Da Book" that comes in the box and enjoy. 40 lbs of propane should keep folks hot and soapy till the fresh water tank goes dry no problem.

Hmmm. 300 lb ice maker and tankless water heater??? Who do I contact to book a fishing trip on the Rose?
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Old 02-15-2013, 09:46 PM   #4
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Our Webasto can heat just the domestic hot water only in the summer. So migjt look at a small diesel boiler.
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Old 02-15-2013, 10:36 PM   #5
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Ron, the paperwork that I have says using lp it burns 120,000-20,000 BTUH. I don't really know what that means. I googled 20# tank holds 366000BTUs. So at an average I will get 3-18.3 hours of water 45 degree warmer than what's in the tank. A shower uses about 2gallons/minute so 120 gallons per hour thus I can heat my entire 1000 gallons of fresh water on less than half of a 20# bottle.
Man the math doesn't seem right.
39 watts electrical consumption
Unit is a Noritz Residential $497.44
Its in the concept phase now, but the biggest grip I hear is the bottles. I have a dingy lift that can easily lift from box lower onto wheelborrow and back again. Maybe I should put my 8d's up there too.
It seams that all these unit raise the water 45 degrees. just more consumption for the bigger models. I guess that's all it does.
I'm digging it.
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Old 02-16-2013, 06:35 AM   #6
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The hassle with Demand stile HW heaters is there is a certain minimum required flow to cause the unit to turn on.

In the galley this is OK as rinsing dishes can be done with HW by using a pitcher.

The hassle comes with taking a shower.

Either the water running with heater on the entire time ,

or if you take a "sailors shower" wet down , soap up, scrub with the water OFF ,

then rinse off the rinse off water will be cold for a while as the heater has shut down from no flow.

My solution is to install a house style shower/ bathtub control valve.

When HW is not required simply select TUB and pipe the heated water back to the FW tank.

This will cost a bit of propane , but no water .

The other style of propane HW hearer is the RV style , which simply keeps a box of water hot just like a house system.

An advantage is that a 12V , 24V or 120V or 240V heater element can heat the water from engine alternator time , solar excess power or simply plugging into the power pole.

The RV is not as "efficient" as HW is on tap 24/7 , but the ease with which Other sources of power can do the heating can make up for this.

The RV works just great if HW hours are kept , and the unit not propane fired 24/7.
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Old 02-16-2013, 08:43 AM   #7
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Fred the paper says .5 gallon/minute minimum. I just don't know what I use when I shower. I guess I need to shower in a bucket and see what I use normally. How do most people take a shower on a boat? At home its full blast all the time. Rv its full blast/off/soap up/rinse. RV tank is about 40 or 50 gallons where boat is 1k gallons. I'm thinking full blast all the time in the boat too.
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Old 02-16-2013, 09:22 AM   #8
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When we use the electric water heater 12 gallon the water is heated for two hours twice a day. Its on a timer. But of course in the winter we use the webasto and/or we do not have dock power. If just water a small boiler would do as you already have the diesel.
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Old 02-16-2013, 09:59 AM   #9
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Ron, the paperwork that I have says using lp it burns 120,000-20,000 BTUH. I don't really know what that means. I googled 20# tank holds 366000BTUs. So at an average I will get 3-18.3 hours of water 45 degree warmer than what's in the tank. A shower uses about 2gallons/minute so 120 gallons per hour thus I can heat my entire 1000 gallons of fresh water on less than half of a 20# bottle.
Man the math doesn't seem right.
39 watts electrical consumption
Unit is a Noritz Residential $497.44
Its in the concept phase now, but the biggest grip I hear is the bottles. I have a dingy lift that can easily lift from box lower onto wheelborrow and back again. Maybe I should put my 8d's up there too.
It seams that all these unit raise the water 45 degrees. just more consumption for the bigger models. I guess that's all it does.
I'm digging it.
Call them up and ask them about the consumption. That will give you an idea about the quality of their customer service as well.

If you're worried about getting the bottles on the flybridge, they weigh less than 40 lb full. I keep a spare on the flybridge and have no problem carrying it up the ladder.
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Old 02-16-2013, 10:17 AM   #10
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We tried one on our last boat and finally threw it overboard. Almost impossible to maintain constant temp when taking a shower. Unless you set it up as suggested by FF I wouldn't consider one.

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Old 02-16-2013, 11:26 AM   #11
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Fred the paper says .5 gallon/minute minimum. I just don't know what I use when I shower. I guess I need to shower in a bucket and see what I use normally. How do most people take a shower on a boat? At home its full blast all the time. Rv its full blast/off/soap up/rinse. RV tank is about 40 or 50 gallons where boat is 1k gallons. I'm thinking full blast all the time in the boat too.
On my boat we get wet, turn the water off, soap and scrub, then turn the water back on to rinse. Of course, I have 60 gallons not 1,000 gallons.

If we're at a dock with electricity, the electric part of the water heater takes care of the heating. At anchor, if we've run for a couple hours, the engine heat has heated our water. It stays hot enough for several hours.
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Old 02-16-2013, 11:54 AM   #12
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This is a hybrid of FF's idea and a tree huggers idea.
green architecture notes On Demand Retrofit Hot Water Recirculation Systems
Edit: after looking at FF's plan his is much better than this.
Edit 2: after thinking about FF's plan you could use the diverter valve as the hot water valve, the shower head out put would be the hot side of the mixer and the tub part of the diverter would be the loop back to the cold water tank.
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Old 02-16-2013, 12:34 PM   #13
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Why not simplify further and just loop the hot water line through the whole boat back to a tee in the cold water inlet to the water heater with a small circ pump? It'll cost you a few feet of pipe and a couple watts of power. There is zero water loss, minimal power use. You can throttle your shower anyway you wish and never have a temperature variance.

It's simple and done all the time in commercial installations. A check valve is added at the cold water between the tee and shut off valve at the water heater.
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Old 02-16-2013, 12:36 PM   #14
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We have a webasto boiler and everhot tankless heater. It works great - unlimited really hot water. The webasto also heats a loop that goes through the engine heat coil in the electric hot water heater and pre-heats the engines. When the engines are running the engine heat is transferred to the cabin/hot water heating system. Check out Sure Marine they have everything you need and are really helpful! They are in Seattle but will ship anywhere.

Suremarine.com
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Old 02-16-2013, 12:38 PM   #15
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By the way, the Webasto unit burns very little Diesel, super efficient.
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Old 02-16-2013, 12:58 PM   #16
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We had a Webasto on our last boat and loved it, but for heat. We did add a "summer loop" for the added benifit to heat hot water only. But to buy one for only hot water? That's over $3,000 for the cheapest unit with no parts. I'm not sure he needs heat, living on the Gulf.

When we were in NZ, most of the houses had on demand hot water heaters. It seemed a lot of them were made by Bosh. They aren't the cheapest but at a little over $400, that didn't sound to bad.
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Old 02-17-2013, 11:56 AM   #17
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"I'm thinking full blast all the time in the boat too."

Then use the hot circulating water in the noisemaker with a marine heater as you create 1000gal of RO for a shower.

The not required demand heated water is risky to use as a supply as most HW heaters expect cool water , not hot water as their supply.It might just shut down.

Simply plumbing it back into the FW tank , has zero tech risk.
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Old 02-17-2013, 05:37 PM   #18
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I put an ITR Hurricane into Island Eagle. I have not been particularly happy with it. You might want to take a look at the Toyoset:
Toyotomi U.S.A. - Instantaneous Oil Fired Water Heater - OM-148
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Old 02-17-2013, 08:23 PM   #19
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I put an ITR Hurricane into Island Eagle. I have not been particularly happy with it. You might want to take a look at the Toyoset:
Toyotomi U.S.A. - Instantaneous Oil Fired Water Heater - OM-148
IslandEagle, The best info I could find on the hurricane was the max output was 50000btuh, where as the one I looked at was 120k btuh and the toyotomi was 180k btuh, almost 3 times the heating of your unit. Do you know how much the toyotomi unit is? I sure would consider it because it can run off of #2 desiel. Good find
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Old 02-18-2013, 03:22 PM   #20
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IslandEagle, The best info I could find on the hurricane was the max output was 50000btuh, where as the one I looked at was 120k btuh and the toyotomi was 180k btuh, almost 3 times the heating of your unit. Do you know how much the toyotomi unit is? I sure would consider it because it can run off of #2 desiel. Good find
I'm pretty sure the Toyoset price is pretty reasonable. Much better than anything "marine", that's for sure.

Two other comments, now that I see the size of boat it's going into:

1) You should seriously consider some solar heaters up on the cabin roof. In your climate, most days you'll have all the hot water you want, totally free.

2) If you have a good place to put it (outside on the back deck?) you might want to consider a house-style high-efficiency propane hot water heater.

Scott
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