# Hot Water Tank - Questions I've been asked



## Franklingower (Oct 12, 2010)

Electric Hot Water Tank.

Holiday cottage

When you leave your cottage in the fall, most people turn off the power, shut off the water and open a tap.
Returning in the spring, some will turn on the power, turn off the tap and turn on the water. 
3 seconds after turning on the power, the top element burns out because the element must be immersed in water at all times and the top of the tank is air. Get all the air out of the pipes before turning on the power. 

Heating power in the Tank

Each standard residential electric water tank has two 3000 watt at 240V elements installed on a flip flop basis, only one will heat at a time. This will produce a flow of 12.5 amp. The resistance in the element is 240/12.5 or 19.2 Ohms.
With a constant resistance of 19.2 Ohms, If the voltage is 250 this will produce 3,255 Watts. 

Voltage in a home is dependent on the distance from the transformer on the pole to the home and the number of residences on that transformer. The voltage can fluctuate from a high of 255 to a low of 220.
Light bulbs will burn out faster at the high voltage but motors will run at a lower amperage.

1000 watts (1Kw) = 3412 BTU's So a tank with 240 Volt supply and a 3Kw element, will put out 3412 X 3.0Kw = 10,236 BTU's 

Note: An electric water tank is 100% efficient. All of the heat goes into the water. Any gas water tank has some of the heat going up the chimney. 

Amperage of the standard 19.2 Ohm element with varying voltages.

120 Volts = 750 Watts 6.2A Wire with #14 (white) wire & Single 15 amp breaker
208 Volts = 2253 Watts 10.8A Wire with #14 (white) wire & Double 15 amp breaker
240 Volts = 3000 Watts 12.5A Wire with #12 (yellow) wire & Double 20 amp breaker
250 Volts = 3250 Watts 13.0A Wire with #12 (yellow) wire & Double 20 amp breaker

I've often wired a standard water tank with 120 volt supply to cut the amperage down. This will give you the storage capacity of the tank, but slow recovery. 


If you want more hot water than the standard tank with a flip flop thermostat will put out, you can have both elements come on at the same time by replacing the top thermostat and the over temp cutout with a larger wattage cutout and a thermostat that allows separation of the top and bottom element. With this arrangement both elements can operate at the same time giving a total wattage of 6 Kw. and 20,472 BTU (at 240 Volts).
Amperage is 25. Wire with 2#10 (Orange) and 2Pole 30 amp breaker.
Older tanks had an over temp cutout that would handle the wattage and the top thermostat could be rewired to accommodate separate control. 
Contact the tank manufacture for correct parts and approval

If your tank has lasted a long time but an element has burned out. Scratch the tank with a knife. You just may have one of the rare bronze tanks made by Elco in the 60's. Replace the element. Don't throw out the tank.

Water pumped into a storage tank

Water weights 62.4 lbs per cubic foot. Their are 1728 cubic inches in a cubic foot. If you pumped water from a well and wanted about 60 PSI from a water tank on a stand, then the tank would have to be 1728 inches off the ground (144 feet).

BTU's

One pound of water will increase in temperature 1 deg in one hour for every BTU.
One Kw will produce 3412 BTU's 
A full 40 US Gal water tank weighs 334 lbs (if converted to metric, it still weighs 334 lbs).
Raising the temperature from 50 deg to 120 deg will require – 

with 750 watts 9.13 hours
with 2250 watts 3.04 hours
with 3000 watts 2.28 hours
with 3250 watts 2.10 hours
with 6000 watts 1.14 hours.


Water Expansion.

Water expands at the rate of .000214 for each degree Fahrenheit.
If the cold water coming into the tank is at 50 deg. And is heated to 150 degrees. The added expansion is 100 X .000214 or 0.0214. 
For a 40 gallon tank this means that 40 X .0214 or .856 of a gallon is added.
Unless you leave the cold tap dribbling or have an expansion tank, the water tank will expand to accommodate the added volume. The pressure relief valve will spring open and you could have water on the floor. If you do this often, the tank will fail or you may have a washing machine hose burst.
Pressure does not go back to the street due to the Pressure Reducing Valve (PRV). Water flows through a PRV in one direction only.


Water Temperature

Most electric water tanks come from the factory with the thermostat's set at 150 deg. F.
The temperature is set this high so that lots of cold water must be mixed to get the desired temperature and the hot water in the tank will last a lot longer.
I turn down the temperature to 115 deg so that no cold water need be mixed and the water will not scald anyone. Also the cost of maintaining 115 deg water is considerably less than 150 deg temperature. 
At a lower temperature, expansion of your tank will be reduced increasing it's life.
A standard water tank in my home has lasted for 20 years or more.

Make sure to drain out the silt at the bottom of the tank every year with a garden hose connected to the bottom tap. 

Wiring

Use a piece of 7/16 flex and an angle connector to protect the cable on top of the tank. Use #1 straps to hold it down.


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## PlugsAndLights (Jan 19, 2016)

Thoughts on replacement of anode? Necessary, how often, etc..
P&L


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## MechanicalDVR (Dec 29, 2007)

PlugsAndLights said:


> Thoughts on replacement of anode? Necessary, how often, etc..
> P&L


This all depends on water chemistry. Once you know when the first one is gone you have the time factor that it lasts. 

Sometimes you know it's done when the water smells off.

My favorite is when you go to pull it out and the only thing left is the center rod and all the magnesium is gone.


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## matt1124 (Aug 23, 2011)

A.O. Smith rep told me to use aluminum rods in this area to reduce the slime we were getting in the large 100 gallon commercial ones I changed out the other day. The sacrificial rod will depend on your water chemistry. 

Thanks for the post. I had to read up the other day about flip flop elements, for some reason dual 3500kw elements on #10 coming off the top wasn't registering right in my head!


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## A Little Short (Nov 11, 2010)

One thing I found out was when my water wouldn't stay hot after running for a while. I thought lower element and changed it. That didn't help so I checked everything including both stats. Turns out the fill tube was broken off and allowing cold water to enter the top.

I tried to change it out but it was stuck, couldn't even heat the fitting and get it out. So I had to replace the tank.

Moral of the story, it's not always the elements or thermostat!


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## eddy current (Feb 28, 2009)

When I wrote my licence (was using the 1998 code) I had a question on HWT's that drove me crazy. I contested it (along with 50 other bad questions) and they gave me this code reference 26-750(2). (Old code, not in the new book)

Here was the question.
A home owner asks you to lower the temp in their HWT 20 degrees. What temp do you set it to?

I contested that I am not a plumber and should not be asked this question. Besides, what temp are we starting at?

The answer I got back was that because 26-750(2) says the temp device will regulate the temp not to exceed 90, that is my starting point. The answer was 70 degrees.

WHAT????? What device is this? It comes that way from the factory!!! Stupid C of Q.

Sorry, HWT / C of Q rant over


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## MechanicalDVR (Dec 29, 2007)

eddy current said:


> When I wrote my licence (was using the 1998 code) I had a question on HWT's that drove me crazy. I contested it (along with 50 other bad questions) and they gave me this code reference 26-750(2). (Old code, not in the new book)
> 
> Here was the question.
> A home owner asks you to lower the temp in their HWT 20 degrees. What temp do you set it to?
> ...


LOL 90 barely feels warm!


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## PlugsAndLights (Jan 19, 2016)

eddy current said:


> When I wrote my licence (was using the 1998 code) I had a question on HWT's that drove me crazy. I contested it (along with 50 other bad questions) and they gave me this code reference 26-750(2). (Old code, not in the new book)
> 
> Here was the question.
> A home owner asks you to lower the temp in their HWT 20 degrees. What temp do you set it to?
> ...


 :laughing: Yep, stupid question. :laughing: 

Don't remember any really stupid ones when I wrote in '07. 
P&L


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## emtnut (Mar 1, 2015)

PlugsAndLights said:


> Thoughts on replacement of anode? Necessary, how often, etc..
> P&L


On City water, 2-4 yrs

On well water, depends what's in the water as Mech said.

Cathodic protection really extends the life of the hwt .... unless the rod looks like this :blink:


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## sbrn33 (Mar 15, 2007)

Pretty much every single cold water heater I have ever wired in a resi setting has been 4500 watt elements.
Also if one of my guys wired a 240 volt water heater on 120 he would be fixing it on his own time.


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## emtnut (Mar 1, 2015)

eddy current said:


> When I wrote my licence (was using the 1998 code) I had a question on HWT's that drove me crazy. I contested it (along with 50 other bad questions) and they gave me this code reference 26-750(2). (Old code, not in the new book)
> 
> Here was the question.
> A home owner asks you to lower the temp in their HWT 20 degrees. What temp do you set it to?
> ...


Test writers :no:

Answer would be 20˚ less than it was set at, or 90˚ ... whichever is lower:jester:


**edit** so, you only got 99 on the test then :no:


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## CADPoint (Jul 5, 2007)

Nice essay, I filed it!


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## jbfan (Jan 22, 2007)

MechanicalDVR said:


> LOL 90 barely feels warm!


90 C or F?


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## MechanicalDVR (Dec 29, 2007)

jbfan said:


> 90 C or F?


I'm talking Fahrenheit, 90c would be 194F which would be close to boiling and I've never seen that come out of a water heater. 

That would turn to steam as soon as you opened a tap and dropped the pressure.


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## jbfan (Jan 22, 2007)

MechanicalDVR said:


> I'm talking Fahrenheit, 90c would be 194F which would be close to boiling and I've never seen that come out of a water heater.
> 
> That would turn to steam as soon as you opened a tap and dropped the pressure.


The OP is in Canada, so I assumed C.


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## MechanicalDVR (Dec 29, 2007)

jbfan said:


> The OP is in Canada, so I assumed C.


True, and I would have as well until he said 90deg.


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## Franklingower (Oct 12, 2010)

sbrn33 said:


> Pretty much every single cold water heater I have ever wired in a resi setting has been 4500 watt elements.
> Also if one of my guys wired a 240 volt water heater on 120 he would be fixing it on his own time.
> __________________
> I still can't believe you even posted that trash.
> ...


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## Franklingower (Oct 12, 2010)

Should have mentioned that the bulb was rated at 240 volt that I reduced to 120V, so would get 25W.


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## PlugsAndLights (Jan 19, 2016)

sbrn33 said:


> Pretty much every single cold water heater I have ever wired in a resi setting has been 4500 watt elements.
> Also if one of my guys wired a 240 volt water heater on 120 *he would be fixing it on his own time*.


Maybe we should start a "Why I'd never work for Sabrina" thread. :jester:
P&L


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## sbrn33 (Mar 15, 2007)

PlugsAndLights said:


> Maybe we should start a "Why I'd never work for Sabrina" thread. :jester:
> P&L


Hell, I would fire your ass just for calling it a hot water heater.


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## emtnut (Mar 1, 2015)

You'd NEVER fire me .... You can't afford me :jester:


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## sbrn33 (Mar 15, 2007)

emtnut said:


> You'd NEVER fire me .... You can't afford me :jester:


You don't know that. I pay my helpers very well.


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## PlugsAndLights (Jan 19, 2016)

sbrn33 said:


> Hell, I would fire your ass just for calling it a hot water heater.


Never actually noticed. Reminds me of my grandmother scolding me 
for saying "potato peeler". Fine then; vegetable peeler, sheesh. 
P&L


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## emtnut (Mar 1, 2015)

sbrn33 said:


> You don't know that. I pay my helpers very well.


I pay my subs well  .. Whatchu sayin ? :jester:


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## MechanicalDVR (Dec 29, 2007)

PlugsAndLights said:


> Never actually noticed. Reminds me of my grandmother scolding me
> for saying "potato peeler". *Fine then; vegetable peeler, sheesh*.
> P&L


So you grew up with help in the house?


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