Water heater questions

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K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
After reading some questions about premature element failure I came up with some questions about water heater design.

Are the elements in a wet or dry well? That is, do they come in direct contact with the water, or do they go in a tube instead?

I have read about 'anode rods' and how they should be checked and/or replaced. I have never heard of that before. Is that for gas or electric heaters or both?

Thanks!
 

kwired

Electron manager
Location
NE Nebraska
Heating element is in direct contact with water, but the outer surface does have an insulating layer between it and the current carrying component. If there is a breakdown in this insulating layer you usually have pretty rapid progression toward fatal failure of the effectiveness of the element.

Many spa heaters will have a minor enough insulation breakdown that is not really visibly noticeable but will leak enough current to trip the GFCI protecting the spa circuit.

Range top elements are similar in construction, if you placed a metal cooking pan directly on the current carrying portion of the element, you would electrically bridge segments of the element and probably have a lot of "fireworks" when using it.

I don't know what they use for the insulating material, would think it has to be something with good thermal properties - which is not so easy to come by with electrical insulating materials, so there is still likely some significant heat transfer resistance in there.
 

growler

Senior Member
Location
Atlanta,GA
Are the elements in a wet or dry well? That is, do they come in direct contact with the water, or do they go in a tube instead?

A bit of trivia....A normal modern water heater will have an element that comes in contact with the water but they did make a version where the element was in a dry tube ( looked like a regular heater element). I replaced one at one time for a neighbor, I was surprised to find a replacement part. The one I saw was only about 10 gallons and was under a sink but they may have made larger units.
 

jumper

Senior Member
A bit of trivia....A normal modern water heater will have an element that comes in contact with the water but they did make a version where the element was in a dry tube ( looked like a regular heater element). I replaced one at one time for a neighbor, I was surprised to find a replacement part. The one I saw was only about 10 gallons and was under a sink but they may have made larger units.

That type of set up would make changing the element easier since you would not have to drain the tank, but I wonder if it would be as efficient as a WH with elements that are in direct contact with the water. IDK.
 

jbelectric777

Senior Member
Location
NJ/PA
The biggest problem with open elements or premature open elements is non experienced persons installing or replacing an electric hot water heater by turning the circuit on before the elements are submerged. Those that know how they work also understand the concept that only one 5KW element is energized at a time. Heat rises, so the bottom element energizes first, when that thermostat is satisfied one leg (on the bottom stat) is energized to the top and so the cycle goes.
 

growler

Senior Member
Location
Atlanta,GA
That type of set up would make changing the element easier since you would not have to drain the tank, but I wonder if it would be as efficient as a WH with elements that are in direct contact with the water. IDK.

I doubt that the heat transfer is very good and probably takes longer to heat a tank of water. I was also surprised the heater element didn't burn out so I don't think it was getting all that hot and was only 120V.

I think this one was used before the tankless heater to have a small heater right at the point of use. Back years ago you would see this sort of thing in Europe, a small water heater at the kitchen sink and another in the bathroom. I have seen some where you would only run the amount of water to be heated 2-3-4 gallon ( or X liters ) into the heater and then push the start button and only heat that amount.

It's hard to beat the efficiency of a moderm water heater if you properly insulated the pipes.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Ooops. Screwed that one up. I should have stuck with element.:slaphead:

I wonder what it actually does. Diagram I pulled up labeled it as "sacrificial anode rod."
The purpose is similar to cathodic protection on boats and buried pipes.
It is there so that stray currents and chemical action from the water will be less likely to corrode through the steel tank (if there is also a break in the glass liner of lined tanks.)
The sacrificial anode will be corroded away slowly instead of the same reaction happening in the tank wall.
Once the anode is consumed, the tank is next in line, but very few people regularly pull out the anode for inspection and replacement if necessary.
 

GoldDigger

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Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Depending where the water heater is located, quick hands and a shop vac can eliminate the necessity of draining the tank!! :p

It is, however, best to turn off the cold water feed so that you are not trying to insert the new element against full line pressure.

(I once had a novice gas tech try to lubricate the main shutoff valve at my house (before the pressure regulator) while the valve was under pressure. The core popped out and he could not get it back in again.
Four hours of repair by a five man PG&E crew who had to dig up the main on the other side of the street and insert a new feeder tap with a valve to replace the line that they had to pinch off to stop the gas flow. )
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
It is, however, best to turn off the cold water feed so that you are not trying to insert the new element against full line pressure.

(I once had a novice gas tech try to lubricate the main shutoff valve at my house (before the pressure regulator) while the valve was under pressure. The core popped out and he could not get it back in again.
Four hours of repair by a five man PG&E crew who had to dig up the main on the other side of the street and insert a new feeder tap with a valve to replace the line that they had to pinch off to stop the gas flow. )

That's a lotta omph! on the street side. What is the typical street side pressure?
 

Frank DuVal

Senior Member
Location
Fredericksburg, VA 21 Hours from Winged Horses wi
Occupation
Electrical Contractor, Electrical Engineer
Anode rod is to be the sacrificial part to be eaten by the mineral hungry water instead of the steel tank. Yes, when the anode rod goes away, the tank follows quickly with holes. So an anode rod is in most every water heater, not just electric models.

In a quick recovery electric water heater, the one with two elements, the Upper one comes on first, as since hot water rises, it is closer to the hot water exit on top of the tank. After the top element thermostat is satisfied with hot water, the Lower element comes on and finishes heating the rest of the water in the tank.

To illustrate, you take a long shower. Suppose the tank is full of hot water, as no one has used it in a while. As the hot water is used and cold water enters the tank, at the bottom, the bottom element turns on. If your shower continues and you use so much water the top element thermostat gets cool, it turns on the upper element. Now this top element can heat the smaller quantity of water at the top of the tank quicker than the bottom element can heat all of the water in the tank. So you still get some hot (warm) water to finish your shower. As the upper thermostat is satisfied, it turns off and turns on the circuit to the bottom thermostat. When the lower thermostat is satisfied, all the water in the tank should be hot (set temperature).

Frank DuVal
 

GoldDigger

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Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
An excellent summary of the process. You just left out that the bottom thermostat will come on first when you take a shower. When the cold water gets near the top the top thermostat steals the power away from the bottom element and sends it to the top instead.
In the good old days the bottom element only was often on a timer with a separate meter to heat the rest of the tank with lower cost off-peak power.
 

mike_kilroy

Senior Member
Location
United States
We and others pull out our anode rods and discard them.

We use that top hole then to build a double wall recirculating heating element to bottom drain with a tee to heat our tank with ok our outside wood boiler furnaces

No anode rod now 20yrs and still same tank. Today's glass lined tanks dont need it Anymore.
 
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