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Old 11-09-2013, 08:33 AM   #1
gar
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Is 'free' hot water worth it?

Hi All, Heading south on the icw, had an issue with my hot water heater. My fresh water pump started to run a few seconds at a time. Thinking I had a pipe or fitting leaking, I lifted the engine hatch. We had been docked for over a day. I found hot water & antifreeze gushing out of the plastic engine expansion tank. Cut off the engine valves to & from the hot water heater & all stopped. I guess the internal exchanger in the hot water heater developed a leak. Needless to say, I have to replace the 6 gal water heater-it's 14 years old. I am thinking of doing away with the engine exchanger, as if this had happened while underway, antifreeze could have gotten into the water system? I don't have much call for hot water underway, but it is an nice feature. Any input is appreciated.
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Old 11-09-2013, 08:52 AM   #2
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Do you anchor out. If not the hot water underway is not a big deal. If you anchor out then the hot water when you get to your anchorage is important.

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Old 11-09-2013, 09:24 AM   #3
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I'd buy a good quality potable hot water heater with heat exchanger and be done with it.

Stuff fails on boats. Your Hot water heater sounds like it worked fine for a decade and a half. Thats a pretty long time.

Water heaters with heat exchangers are in almost every boat I've ever seen. Reported failures of the heat exchanger are not very common.
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Old 11-09-2013, 10:59 AM   #4
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My last 3 boats did NOT have a water heater "loop". If you want hot water at the anchorage, fire up the generator 30 minutes before you get there. Those hot water heaters work quickly. And if you're scared to fire up the generator(like some people appear to be), then uninstall that thing while you are at it...
I had a Beneteau sailboat with a water heater loop. I am trying to remember what happened it has been so long ago. But something in the loop got clogged. And there was a bypass. But it stunted the flow of coolant enough to cause the engine to overheat at anything other than idle power. I chased my tail for a week trying to figure out what was causing the overheat. I then bypassed the loop and everything worked great. Not that the tank or loop did not rupture. So the water heater remained to work on AC power only.
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Old 11-09-2013, 01:52 PM   #5
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I'll tell you what. . . those heat exchanger water heaters can be dangerous!! I Took a shower after a long day of fishing and just about lost all the skin off my feet before I could get the hot water shut off.

180 degree water verses 100 degree water is a lesson I won't soon forget!!

All kidding aside. . . if you have small children on board, their parents need to be aware of this and monitor their bath time!!
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Old 11-09-2013, 01:59 PM   #6
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The way I view a water loop to the water heater is that it in effect acts as a hybrid device of sorts. You can heat as the previous post suggest with the genset but the heat is free from the main engine(s). Why burn additional diesel and add time to the genset when it is already there?

I can see some would freak at the thought of glycol in their water heater.. but do you use hot water to drink from the boat? As the water pressure in the fw side of the system is at 30+- lbs will the engine glycol actually make it to the fresh side.. unless the water pressure side is off?

The other way to view it is that most boats are plumbed this way... how many of you have had the exchanger fail.. most times the water heater tank fails first.
I feel the O.P. got great life from the water heater.. replace the water heater in the current configuration and go boating
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Old 11-09-2013, 02:03 PM   #7
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I'll tell you what. . . those heat exchanger water heaters can be dangerous!! I Took a shower after a long day of fishing and just about lost all the skin off my feet before I could get the hot water shut off.

180 degree water verses 100 degree water is a lesson I won't soon forget!!

All kidding aside. . . if you have small children on board, their parents need to be aware of this and monitor their bath time!!
Add a mixing valve to the system and never worry again..
I know there is a formula to figure it but the little 6gal water heaters with 180 deg. water in them mixed down to 105 or so give out a lot of hot water from a small footprint
Mixing valves are cheap

Honeywell Thermostatic Mixing Valve-AM101C-US-1 at The Home Depot

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Old 11-09-2013, 02:13 PM   #8
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hot water free from the engine can be really nice as my girlfriend loves to shower about an hour before pulling into port and having it to do dishes and wash hands all day is really nice.

for those concerned about high temps...there are mixing valves that regulate the hot water tanks temp.

I just added a bus heater system and was worried that it increased the possibility of a coolant leak and affecting my single engine. So I bought a little solar system pump and heat exchanger for around $300 including all the hose and fittings and simplified the old system so the chances of a leak into my coolant or coolant into my fresh water is somewhat reduced.
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Old 11-09-2013, 02:53 PM   #9
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One of the often overlooked delights of a marine HW heater compared to home cheapo is the marine unit has a sensor that will pop if the unit is turned on with a dry tank.

Reset is a quick push of a button.

Stuff happens , when it does its nice for it to be a non event.

WE have one and love it as well as a box heater to steal heat in cooler weather underway.
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Old 11-09-2013, 03:03 PM   #10
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One of the often overlooked delights of a marine HW heater compared to home cheapo is the marine unit has a sensor that will pop if the unit is turned on with a dry tank.
How's that work? Got a part number or dataplate info on that sensor?
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Old 11-09-2013, 03:30 PM   #11
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One of the often overlooked delights of a marine HW heater compared to home cheapo is the marine unit has a sensor that will pop if the unit is turned on with a dry tank.
I didn't know this either. I replaced my tank 2 years ago with a Raritan marine unit and this was not mentioned in the manual that I remember.
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Old 11-09-2013, 03:36 PM   #12
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Hi All, Heading south on the icw, had an issue with my hot water heater. My fresh water pump started to run a few seconds at a time. Thinking I had a pipe or fitting leaking, I lifted the engine hatch. We had been docked for over a day. I found hot water & antifreeze gushing out of the plastic engine expansion tank. Cut off the engine valves to & from the hot water heater & all stopped. I guess the internal exchanger in the hot water heater developed a leak. Needless to say, I have to replace the 6 gal water heater-it's 14 years old. I am thinking of doing away with the engine exchanger, as if this had happened while underway, antifreeze could have gotten into the water system? I don't have much call for hot water underway, but it is an nice feature. Any input is appreciated.
It's not up to you, ask your wife
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Old 11-09-2013, 03:57 PM   #13
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My new tank does this too. I haven't really checked it out, but I'm assuming it is an overtemp sensor to protect the element. When it pops it stops a melt down, but probably not something you want to do on a regular basis. It's only happened to me once.

Your Atwood electric water heater is equipped with a high quality 120 volt/1400 watt Incaloy® heating element designed to withstand accidental operation in an empty tank. An optional 220 volt/1500 watt version is also available. The electrical system is ignition protected and meets UL specifications and is UL Marine approved.
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Old 11-09-2013, 09:13 PM   #14
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If your alternator and inverter are up to the task then a 110V WH without the loop will work fine to get you good toasty water while underway. We often use the 110v side as the heat exchanger in our old WH is not up to the task. That said we have two 108a alts.
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Old 11-10-2013, 05:40 AM   #15
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My new tank does this too. I haven't really checked it out, but I'm assuming it is an overtemp sensor to protect the element. When it pops it stops a melt down, but probably not something you want to do on a regular basis. It's only happened to me once.
That red button is the reset on an overtemp switch set to open if the water reaches around 170F which can happen if the thermostat sticks closed.

It senses the water temperature by "feeling" the metal tank wall. It doesn't have a clue what's happening to the element, or if the tank is cool because it is empty.
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Old 11-10-2013, 06:36 AM   #16
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Just a curious "rookie" questions, but what about solar to heat the water during the day? I realize there could be some drawbacks, but just wondering if that's at all feasible?

OD
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Old 11-10-2013, 07:01 AM   #17
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Just a curious "rookie" questions, but what about solar to heat the water during the day? I realize there could be some drawbacks, but just wondering if that's at all feasible?

OD
For many years sailors have used "solar shower" bags to do just that...I/we used them in Ft Lauderdale for a year till our "pirate" marina installed a curb throwaway makeshift hot water heater/shower in the mangroves.

My guess is that it's running the plumbing topside that deters people then it's the weight and looks of collectors that again deters them.

I just bought a pump thet's advertised for solar systems that is 12V, uses 10W of energy and is marketed to be run off a solar panel to pomp when collectors are heating. If I was going to swing on the hook for long periods, I might build a removable parabolic collector (much smaller) and add it to my hydronic loop with quick disconnects.
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Old 11-10-2013, 07:04 AM   #18
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Solar can work , but the surface area of the heating tank is large.

To use excess solar power from a panel could be done as 12v and 24v heating elements are made. Most are only 50Watt , so not strong.

Backwoods Solar has them.
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Old 11-10-2013, 07:25 AM   #19
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I wonder just how big a collector really has to be. Consider how hot the water in a garden hose gets in a very short period in the Sun.

I use some black 3/4 tubing as part of a drip irrigation system mainline and several times have had it fail from high temperature when pressurized with no flow. It would be interesting to install a temporary loop of that stuff (it's dirt cheap) on the upper deck and circulate water from the heater just to measure the heat gain.
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Old 11-10-2013, 07:51 AM   #20
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I wonder just how big a collector really has to be. Consider how hot the water in a garden hose gets in a very short period in the Sun.

I use some black 3/4 tubing as part of a drip irrigation system mainline and several times have had it fail from high temperature when pressurized with no flow. It would be interesting to install a temporary loop of that stuff (it's dirt cheap) on the upper deck and circulate water from the heater just to measure the heat gain.
What???? No formula?????

I remember making the parabolic heaters in Boy Scouts and cooking hot dogs...further reading lead me to a site that discussed how a 3-4 foot parabolic reflector about 18 inches high could get water near boiling if slowly passed through it.,,but that was back when we would be feeding the world through fish farms by the year 2000 so while I'm dying to experiment with one...it's not very high on my project priority list.

The black hose around the deck would probably work great on really sunny days like the solar showers....and you can't any simpler...I think the trick with solar anything is how to enhance it for most days, even the overcast ones (the rest of the days are better for staying in bed or watching the rain from a Tiki bar )
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