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Old 28-04-2018, 08:34   #1
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Hot Water Heater Longevity

A cruising friend told me that he leaves his hot water heater on all the time, even when they are not on the boat because keeping hot water in the tank prevents it from rusting inside the tank.

Has anyone else heard of this theory, or have any thoughts on its validity?

Thanks

Glenn Tuttle
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Punta Gorda, FL
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Old 28-04-2018, 08:54   #2
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Re: Hot Water Heater Longevity

Quote:
Originally Posted by Parrothedd View Post
A cruising friend told me that he leaves his hot water heater on all the time, even when they are not on the boat because keeping hot water in the tank prevents it from rusting inside the tank.

Has anyone else heard of this theory, or have any thoughts on its validity?

Thanks

Glenn Tuttle
GB-46
Tothill
Punta Gorda, FL
As far as I know water heaters are either stainless steel or porcelain coated on the inside. I think constantly cycling on and off cooling and heating might be slightly worse than keeping the shell hot all the time. No scientific evidence to either prove or disprove this theory. I just changed out the heating element in mine. It was starting to leak. P.I.T.A.
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Old 28-04-2018, 09:23   #3
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Re: Hot Water Heater Longevity

My home hot water is on all the time and they apparently rust readily. I doubt there is much difference really, but if you have a SS one I suppose the elevated temp could actually make it corrode faster.....?
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Old 28-04-2018, 09:40   #4
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Re: Hot Water Heater Longevity

I see this more of an issue on a cast iron boiler (for home) than a water heater. The real damage is done when fittings and connections repeatedly shrink and expand. With better materials and fewer connections on a water heater, and their already-short lifespan, it probably won't make any noticeable difference.

PS: Someone is bound to mention that you don't need to heat water if it's already hot. Thus "hot water heater" would be redundant. There, got that out of the way!
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Old 28-04-2018, 09:45   #5
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Re: Hot Water Heater Longevity

Quote:
Originally Posted by Parrothedd View Post
A cruising friend told me that he leaves his hot water heater on all the time, even when they are not on the boat because keeping hot water in the tank prevents it from rusting inside the tank.

Has anyone else heard of this theory, or have any thoughts on its validity?

Thanks

Glenn Tuttle
GB-46
Tothill
Punta Gorda, FL
That's crazy. As an ex water treatment corrosion control guy, corrosion rates double of roughly every 10 degrees higher temperature. But whether a hot water heater lasts 10 years or 12 years matters little probably.

But, the boat hot water heater is small and if you want hot water when you show up uo leave it on.
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Old 28-04-2018, 09:50   #6
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Re: Hot Water Heater Longevity

A lot, likely most water heaters have aluminum tanks.
Better ones donít. As a comparison, I replaced my 30 yr old aluminum tanked water heater when I had to remove it to replace my chainplates. It hadnít failed, or leaked, but I couldnít bring myself to reinstall a 30 yr old water heater.
It spent the vast majority of its life off.
Bad idea to leave on one while your gone in my opinion as it could start to leak, eventually it will be empty and then the heater will burn out, hopefully not catching fire when it does.
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Old 28-04-2018, 09:58   #7
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Re: Hot Water Heater Longevity

I have always had big boats and normally use house or commercial building water heaters. Since I live aboard, they are always on and last as long as they do on land. Just like in a house, the tank should be drained occasionally to remove sediment that can react with the tank coating. The only problem I've had is an older water heater in heavy seas and pounding conditions will sometimes break the electric elements. But they're easy to change and the cost savings are worth dealing with this small problem.
I've only had one yacht type water heater and I wasn't happy with the size or performance.
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Old 29-04-2018, 09:02   #8
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Re: Hot Water Heater Longevity

We change our the magnesium anode every few years. This extends the life.

We also added diode isolation to the ground wire on the heater. If you put two diodes in series one direction and two diodes in series in the other direction, the ground wire will be isolated from the water heater ground by ~1.2V. This voltage is greater than the electrolytic potential between say a copper ground wire and the water heater steel. So the diodes block any electrolysis. The water heater will still be grounded when voltages higher than 1.2V are involved. We used diodes purchased from Digikey DSE120-12A-ND. These can take 17A and up to 1.2kV.
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Old 29-04-2018, 09:11   #9
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Re: Hot Water Heater Longevity

No information or opinion on your question. Just one smart a** comment - there is no such thing as a hot water heater. If the water was already hot you wouldn't need to heat it. ��

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Old 29-04-2018, 09:32   #10
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Re: Hot Water Heater Longevity

Quote:
Originally Posted by Diesel Bill View Post
As far as I know water heaters are either stainless steel or porcelain coated on the inside. I think constantly cycling on and off cooling and heating might be slightly worse than keeping the shell hot all the time. No scientific evidence to either prove or disprove this theory. I just changed out the heating element in mine. It was starting to leak. P.I.T.A.
My calorifiers have always been copper.

The first one on my present boat lasted about 11 years before developing pinhole leaks which could be brazed shut (the brazing cracked every time the unit heat cycled). I hated scrapping it -- it was a beautiful and beautifully made device, but I couldn't restore the integrity of it and was tired of jets of boiling water. The second, inferior but serviceable one has been OK for 6 years so far.
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Old 29-04-2018, 18:48   #11
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Re: Hot Water Heater Longevity

Iíam using a 32 year old Atwood 11 gallon water heater. I live aboard 9 months of the year and the unit is on anytime Iíam on shore power or the generator is running.
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Old 29-04-2018, 19:07   #12
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Re: Hot Water Heater Longevity

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there is no such thing as a hot water heater. If the water was already hot you wouldn't need to heat it...
...or to leave a water heater on. However, there are many reasons to heat hot water, including to make it boil, produce steam, and I am sure, others, but on modern boats, as in homes, we generally only heat water in the apparatus, if at all, to a certain temp, well below boiling, mostly for washing and cleaning (ourselves and objects). Full steam ahead.
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Old 30-04-2018, 18:57   #13
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Re: Hot Water Heater Longevity

Quote:
Originally Posted by Parrothedd View Post
A cruising friend told me that he leaves his hot water heater on all the time, even when they are not on the boat because keeping hot water in the tank prevents it from rusting inside the tank.

Has anyone else heard of this theory, or have any thoughts on its validity?

Thanks

Glenn Tuttle
GB-46
Tothill
Punta Gorda, FL
Not sure about the rusting, but a friend of mine now that he exhausted the heating elements prematurely and had to replace them disconnects the power, whenever he can.
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Old 01-05-2018, 05:26   #14
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Re: Hot Water Heater Longevity

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My calorifiers have always been.

I learned the hard way with my house that copper is not forever. I thought it was. Lasted 25 years or so and then I had the house replumbed with Pex.
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Old 01-05-2018, 05:37   #15
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Re: Hot Water Heater Longevity

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A lot, likely most water heaters have aluminum tanks.
Better ones donít. As a comparison, I replaced my 30 yr old aluminum tanked water heater when I had to remove it to replace my chainplates. It hadnít failed, or leaked, but I couldnít bring myself to reinstall a 30 yr old water heater.
It spent the vast majority of its life off.
Bad idea to leave on one while your gone in my opinion as it could start to leak, eventually it will be empty and then the heater will burn out, hopefully not catching fire when it does.
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