A dock discussion today failed to reach consensus on how to prolong the life of the water heater. Some folks said they leave it on constantly (while on board) and others argue that it's best to turn it on only when needed. Does anyone know for sure what's best? Don
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Doesn't matter...
The only things that can hurt anything in a water heater are antifreeze, bleach and turning it on with no water in the tank. It doesn't matter whether the water in the tank is hot or cold.
The only things that can hurt anything in a water heater are antifreeze, bleach and turning it on with no water in the tank. It doesn't matter whether the water in the tank is hot or cold.
Hot water heated by motor underway
Perhaps this is a stupid question? Water is heated by the engine while underway. What if you do not fill the water system when you first launch the boat in sppring and motor a number of miles to your yacht club or marina. Is this harmful with little or no water in the hot water tank?
Perhaps this is a stupid question? Water is heated by the engine while underway. What if you do not fill the water system when you first launch the boat in sppring and motor a number of miles to your yacht club or marina. Is this harmful with little or no water in the hot water tank?
10-15 years and it is over.
These water heaters are only going to last so long. I would suggest that you turn it on when you get to the boat and turn it off when you leave. The water is going to corrode the units regardless. We only got about 10-12 years on our unit and it was less than $200 for a new unit. Who really cares, it is a convenience item.
These water heaters are only going to last so long. I would suggest that you turn it on when you get to the boat and turn it off when you leave. The water is going to corrode the units regardless. We only got about 10-12 years on our unit and it was less than $200 for a new unit. Who really cares, it is a convenience item.
Running engine with empty HW tank
The problem with operating any electric hot water tank empty is that the heating element is not immersed in water to dissipate the heat. This will allow it to get much hotter and expand more than it was designed for. Also, since there is no water to conduct heat to the thermostat which normally cycles the element on and off, it may stay on much too long, getting much too hot. IMO this is a design flaw which has existed for decades and continues to exist because it has existed for decades (i.e. because we've ALWAYS done it that way). Any product that is capable of destroying itself is under-engineered. I would like to think that some of the products on the market today have this safety feature built in, but which ones? Anyone? Running the engine simply runs hot coolant through the tank and if there is no water in the tank to dissipate the heat, then it just returns to the engine. No harm done. On the issue of keeping your hot water tank on all the time: Its summer time and many of us have the air conditioner running or at least the hatches open to cool off the boat. Since boat water heaters usually have minimal insulation to keep the size down, why would you want to waste electricity to heat the boat and compete with the A/C or make you less comfortable? Also, most chemical reactions (e.g. corrosion) proceed faster at higher temperature.
The problem with operating any electric hot water tank empty is that the heating element is not immersed in water to dissipate the heat. This will allow it to get much hotter and expand more than it was designed for. Also, since there is no water to conduct heat to the thermostat which normally cycles the element on and off, it may stay on much too long, getting much too hot. IMO this is a design flaw which has existed for decades and continues to exist because it has existed for decades (i.e. because we've ALWAYS done it that way). Any product that is capable of destroying itself is under-engineered. I would like to think that some of the products on the market today have this safety feature built in, but which ones? Anyone? Running the engine simply runs hot coolant through the tank and if there is no water in the tank to dissipate the heat, then it just returns to the engine. No harm done. On the issue of keeping your hot water tank on all the time: Its summer time and many of us have the air conditioner running or at least the hatches open to cool off the boat. Since boat water heaters usually have minimal insulation to keep the size down, why would you want to waste electricity to heat the boat and compete with the A/C or make you less comfortable? Also, most chemical reactions (e.g. corrosion) proceed faster at higher temperature.
Also, which is more efficient?
To leave it on while you're there (a lot for liveaboards) or turn it on only when needed, e.g., for a shower. Some of our electrical gurus outta be able to figure this one out. If you pay your own electricity, it matters. Even if you don't, conservation means something. The power company at my house automatically turns the waterheater off during the day, then back on late evening, so there must be something to it.
To leave it on while you're there (a lot for liveaboards) or turn it on only when needed, e.g., for a shower. Some of our electrical gurus outta be able to figure this one out. If you pay your own electricity, it matters. Even if you don't, conservation means something. The power company at my house automatically turns the waterheater off during the day, then back on late evening, so there must be something to it.
Victor, only a few things wrong with your theory
The heating element IS immersed in water...it has to be to heat the water. And turning on an empty electric water heater destroys the heating element within a minute or two. So it cannot continue to generate any heat. However, it's almost impossible for that to happen once the fresh water tank and water heater have been filled because the water heater cold water inlet is at the bottom and the hot water outlet is at the top. The water heater would have to be deliberately drained via the petcock at the bottom to burn out a heating element. As for expansion, thermostats prevent the water from ever getting that hot. Water heaters are required by law to be equipped with pressure relief valves to relieve any pressure in the event of a thermostat failure...without one, the tank could explode. There's little if any substantive difference in the design of water heaters and the way they work...the only differences between marine and household are size and ignition/spark protection of exposed electrical connections. Raritan is a major mfr of marine water heaters and has excellent drawings on their website of all the wiring and internal parts etc. So you can see how all water heaters are designed by going to http://www.raritaneng.com As for generating heat in the boat, water heaters are a LOT better insulated than you think they are...they have to be or they'd create a fire hazard if anything next to 'em could get hot. Leaving it off when you aren't aboard does make more sense than leaving it on, but only to conserve electricity use.
The heating element IS immersed in water...it has to be to heat the water. And turning on an empty electric water heater destroys the heating element within a minute or two. So it cannot continue to generate any heat. However, it's almost impossible for that to happen once the fresh water tank and water heater have been filled because the water heater cold water inlet is at the bottom and the hot water outlet is at the top. The water heater would have to be deliberately drained via the petcock at the bottom to burn out a heating element. As for expansion, thermostats prevent the water from ever getting that hot. Water heaters are required by law to be equipped with pressure relief valves to relieve any pressure in the event of a thermostat failure...without one, the tank could explode. There's little if any substantive difference in the design of water heaters and the way they work...the only differences between marine and household are size and ignition/spark protection of exposed electrical connections. Raritan is a major mfr of marine water heaters and has excellent drawings on their website of all the wiring and internal parts etc. So you can see how all water heaters are designed by going to http://www.raritaneng.com As for generating heat in the boat, water heaters are a LOT better insulated than you think they are...they have to be or they'd create a fire hazard if anything next to 'em could get hot. Leaving it off when you aren't aboard does make more sense than leaving it on, but only to conserve electricity use.
I burned my element out
Due to water tank was ran low and element was left on when water pressure was turned off. water boiled and evaporated then burned element. That is my theory anyway, I could be wrong. Tim Welsh H34 AKA Cabo Wabo
Due to water tank was ran low and element was left on when water pressure was turned off. water boiled and evaporated then burned element. That is my theory anyway, I could be wrong. Tim Welsh H34 AKA Cabo Wabo
Can't happen that way, Tim...unless
The plumbing from your water tank to the water heater is uphill all the way and the water in the water heater ran back down into the tank when the pump ceased to keep the system pressurized. Unless your water heater is leaking, that's the only thing that would allow all the water to drain out of the water heater, even if the water tank is empty...'cuz the inlet from the water tank is at the bottom. Nor could the water have boiled--the thermostat prevents that...and if the thermostat fails, the water in the water heater wouldn't evaporate, it would be forced out the pressure relief valve as steam. I think you'd know it if that had happened. My guess: your water heater either leaks, or the drain petcock was (is?) either open enough--or needs a new gasket--to allow a drip slow enough that you wouldn't notice it. Most heating element failures occur in the spring...the water heater has been bypassed to winterize the fresh water system and somebody turns on the water heater breaker before it's reconnected.
The plumbing from your water tank to the water heater is uphill all the way and the water in the water heater ran back down into the tank when the pump ceased to keep the system pressurized. Unless your water heater is leaking, that's the only thing that would allow all the water to drain out of the water heater, even if the water tank is empty...'cuz the inlet from the water tank is at the bottom. Nor could the water have boiled--the thermostat prevents that...and if the thermostat fails, the water in the water heater wouldn't evaporate, it would be forced out the pressure relief valve as steam. I think you'd know it if that had happened. My guess: your water heater either leaks, or the drain petcock was (is?) either open enough--or needs a new gasket--to allow a drip slow enough that you wouldn't notice it. Most heating element failures occur in the spring...the water heater has been bypassed to winterize the fresh water system and somebody turns on the water heater breaker before it's reconnected.
Peggie's right again
It doesn't matter, it's simply a matter of heat transfer from the electric element to the water. Heat six gallons takes X amount of watts. Doesn't matter whether it's one gallon per hour over six hours or six gallons in one hour. Same amount of energy. Do you always want hot water when you're there? Then leave it on. It's only 6 or 11 gallons anyway. Ours heats up the hot water in 15 minutes. I turn it off when the water's hot, the insulation in the tank keeps it warm for awhile. If you assume the thermostat works, then it'll turn itself off. This is the electric part. As far as empty when running the engine, it doesn't matter. The engine hot water goes through the HX inside the water heater. If it has nothing to heat, it just keeps going and recirculates. It doesn't matter. Just don't leave it on electric when you're not there. Stu
It doesn't matter, it's simply a matter of heat transfer from the electric element to the water. Heat six gallons takes X amount of watts. Doesn't matter whether it's one gallon per hour over six hours or six gallons in one hour. Same amount of energy. Do you always want hot water when you're there? Then leave it on. It's only 6 or 11 gallons anyway. Ours heats up the hot water in 15 minutes. I turn it off when the water's hot, the insulation in the tank keeps it warm for awhile. If you assume the thermostat works, then it'll turn itself off. This is the electric part. As far as empty when running the engine, it doesn't matter. The engine hot water goes through the HX inside the water heater. If it has nothing to heat, it just keeps going and recirculates. It doesn't matter. Just don't leave it on electric when you're not there. Stu
Peggy, Bad day at the office ???
Peggy, Nobody is questioning your knowledge in this area, but please read all the words in my post. As suggested in the title and first sentence, my entire discussion deals with an empty tank. You address the operation of a full tank. I am talking about the expansion of the element, which is what happens when it destroys itself, not the expansion of the tank. A thermal sensor and cut-off would prevent the element from burning out. The tank on my P42 (probably the original) is definitely not as well insulated as a household tank. The outer can on a typical Sears 40 is barely above ambient temperature. My boat tank when heated is uncomfortable to skin contact for more than a few seconds. Its not going to start a fire, but it definitely heats the surrounding air. This is simply a trade off of insulation efficiency vs making it fit in boat size spaces. Thus, one gallon in six hours would take slightly more energy in the real world than six gallons in one hour due to heat loss during the six hours.
Peggy, Nobody is questioning your knowledge in this area, but please read all the words in my post. As suggested in the title and first sentence, my entire discussion deals with an empty tank. You address the operation of a full tank. I am talking about the expansion of the element, which is what happens when it destroys itself, not the expansion of the tank. A thermal sensor and cut-off would prevent the element from burning out. The tank on my P42 (probably the original) is definitely not as well insulated as a household tank. The outer can on a typical Sears 40 is barely above ambient temperature. My boat tank when heated is uncomfortable to skin contact for more than a few seconds. Its not going to start a fire, but it definitely heats the surrounding air. This is simply a trade off of insulation efficiency vs making it fit in boat size spaces. Thus, one gallon in six hours would take slightly more energy in the real world than six gallons in one hour due to heat loss during the six hours.
Hot Water Heater (More)
Peggie forgot to mention that the electrical heating element in a hot water heater is at the bottom of the tank so that as the water is heated it will rise, bringing cold water down to the element. This means that the heating element can't run dry unless the tank is nearly empty.
Peggie forgot to mention that the electrical heating element in a hot water heater is at the bottom of the tank so that as the water is heated it will rise, bringing cold water down to the element. This means that the heating element can't run dry unless the tank is nearly empty.
Um, Victor
Perhaps you could do what you suggest yourself. Your post started out: "Running engine with empty HW tank: The problem with operating any electric hot water tank empty is that the heating element is not immersed in water to dissipate the heat. This will allow it to get much hotter and expand more than it was designed for. Also, since there is no water to conduct heat to the thermostat which normally cycles the element on and off, it may stay on much too long, getting much too hot." Empty with Running engine shifts immediately to electrical. I don't understand. They're two different things, so like you suggested I went back and read them and still don't understand your response to Peggie's post. See my post above. The electrical element is IN the water. What does that have to do with running the engine on empty? There IS NO thermostat on the engine side when it's running. The only thermostat is on the electrical side. A Thermostat is NOT needed on the engine side, since the engine's only running up to 180 (worst case is 200 +), so the heat transfer simply can't heat the water any higher than the engine side water in the internal HX inside the hot water heater. So, theoretically you could get 160 degree water in the water heater IF you ran your engine for many, many hours at a very high operating temperature. That's why you have BOTH hot and cold faucets. Let's get real. What's the design flaw? C'mon, Peggie's covered and answered your questions every which way but Sunday. I'll go back to my office now, I'm having a good day.
Stu
Perhaps you could do what you suggest yourself. Your post started out: "Running engine with empty HW tank: The problem with operating any electric hot water tank empty is that the heating element is not immersed in water to dissipate the heat. This will allow it to get much hotter and expand more than it was designed for. Also, since there is no water to conduct heat to the thermostat which normally cycles the element on and off, it may stay on much too long, getting much too hot." Empty with Running engine shifts immediately to electrical. I don't understand. They're two different things, so like you suggested I went back and read them and still don't understand your response to Peggie's post. See my post above. The electrical element is IN the water. What does that have to do with running the engine on empty? There IS NO thermostat on the engine side when it's running. The only thermostat is on the electrical side. A Thermostat is NOT needed on the engine side, since the engine's only running up to 180 (worst case is 200 +), so the heat transfer simply can't heat the water any higher than the engine side water in the internal HX inside the hot water heater. So, theoretically you could get 160 degree water in the water heater IF you ran your engine for many, many hours at a very high operating temperature. That's why you have BOTH hot and cold faucets. Let's get real. What's the design flaw? C'mon, Peggie's covered and answered your questions every which way but Sunday. I'll go back to my office now, I'm having a good day.
Stu- Status