Stupid question #158 from me…

Well, I’m going to ask it…

Why don’t they make electric water heaters where both the top and bottom elements can work at the same time? Wouldn’t this be a really high yielding hot water heater? I know that most all homes are not pre-wired for this amount of amps to run at the same time. Maybe it’s because if a 40 amp water heater came on the same time the A/C came on, along with the oven, you would need more then a 200 amp main electric panel.
I’ve just always wondered about this….maybe I just need to get a life…LOL

Thanks,

Mike

heaters

You can order them that way, and I have retrofitted them to do that. Commercial heaters are usually supplied that way. Residential heaters seldom have a need for that much input, and the wiring would be more expensive.

Than

hj said:

You can order them that way, and I have retrofitted them to do that. Commercial heaters are usually supplied that way. Residential heaters seldom have a need for that much input, and the wiring would be more expensive.

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Thanks hj. Good point on residentials heaters seldom have the need. I didn't know that you could order them that way. Now knowing what you've said, I can go get that life...or job...or something...

Thanks,

Mike

The only stupid question is an unasked question that gets you into trouble for not asking.

I replaced the 4500 watt elements with 3000 watt rigs, and in a few moments rewired so that they both came on together. I use this for radiant heating and it really does well. I notice that the elements seem to last forever. I would guess that is because the lower wattage does not "boil" the water at the immediate area of the element - thats the buzz or sound you hear when the high wattage are elements running - now its silent and after years of service the elements dont have calcium build up like the 4500 watters. Calcium- lime whatever builds up on elements and "insulates" them, then they torch themselves. Maybe the MFG prefers that we torch the elements.

You could use 2 - 2500 watt elements and not have to pull new wire.

Wow

Raucina said:

I replaced the 4500 watt elements with 3000 watt rigs, and in a few moments rewired so that they both came on together. I use this for radiant heating and it really does well. I notice that the elements seem to last forever. I would guess that is because the lower wattage does not "boil" the water at the immediate area of the element - thats the buzz or sound you hear when the high wattage are elements running - now its silent and after years of service the elements dont have calcium build up like the 4500 watters. Calcium- lime whatever builds up on elements and "insulates" them, then they torch themselves. Maybe the MFG prefers that we torch the elements.

You could use 2 - 2500 watt elements and not have to pull new wire.

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Hey that’s really a good idea. Did you replace the top thermostat with a “bottom†type thermostat? Unless I’m wrong, (and it does happen every now and then) you should be able to use two 3000 watt elements on and 30 amp, 240 volt circuit, and not have to worry about re-wiring a new circuit. I’ll have to give you a kick back, every time I do a conversion…LOL.

Mike

rewire

What would be the point in rewiring one for two smaller elements? If you do that, you have not increased the efficiency or recovery of the heater, and you DO need to replace the lower thermostat with one that has an ECO device.

I would pull a second feeder to the heater and add the needed breaker, and add the proper disconnects if needed in your city. You would have to label the heater as if it has 2 inputs for power.
As far as how to wire the unit it self. Pull the wires out of the top thermostat and wire nut them off for the bottom. Wire the new wires into the top thermostat.
I would not do this unless it was my own house.

I would run a second water heater in series with the temp turned down lower on the first heater. You could go with a larger commercial unit with the higher recovery rate but you need to do the math on if it supply what is needed. IMO you will get the best recovery rate for the cost with 2 heaters instead of one and gives you the chance to set them up for bypassing so you can work / replace one as needed.

Mikebarone said:

Well, I’m going to ask it…

Why don’t they make electric water heaters where both the top and bottom elements can work at the same time? Wouldn’t this be a really high yielding hot water heater? I know that most all homes are not pre-wired for this amount of amps to run at the same time. Maybe it’s because if a 40 amp water heater came on the same time the A/C came on, along with the oven, you would need more then a 200 amp main electric panel.
I’ve just always wondered about this….maybe I just need to get a life…LOL

Thanks,

Mike

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Because most plumbers know how to size a water heater and you dont need to have both elements on at the same time, if your running out of hot water then you either (A) have the wrong size water heater (B) take very very long showers...

hj said:

What would be the point in rewiring one for two smaller elements?

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Raucina said:

I replaced the 4500 watt elements with 3000 watt rigs, and in a few moments rewired so that they both came on together. I use this for radiant heating and it really does well. I notice that the elements seem to last forever.

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6000 watts would recover faster than 4500, I assume, but maybe the top element does not really do all that much in water that is already hot?

Okay... A dumb question is the one not asked and now we are getting down to the answers. Answers that will prove the engineers at every water heater manufacturer to be out to lunch. Oh Boy!

The question was a good one that essentially asked if the recovery rate on a water heater that had both elements on at the same time would be better than one at a time, and the answer is yes and it is commonly done on commercial electric water heaters. The problem is that if you rewired the water heater to allow both on at the same time with 4500W elements it would draw 37.5 amps... Now you have to rewire the house and install a larger breaker for a project where proper sizing of the water heater would eliminate the added expense.

Then we get into the scenario of replacing the elements with 3000W elements and both on at the same time which will draw 25 amps... Well the good news is the most houses will not need rewiring for this but your gain is fairly small with only 1500W of added heating power. Thats about 1 Mr. Coffee worth added oomph! Hardly worth the effort.

The function of the top element is to extend the last bit of hot water available and make a small amount immediately available for use rapidly after depletion. It turns off fairly rapidly and switches over to the bottom element that is the workhorse of any water heater.

Size the water heater right and maintain it. The engineers really did get it right.

Redwood said:

The problem is that if you rewired the water heater to allow both on at the same time with 4500W elements it would draw 37.5 amps... Now you have to rewire the house and install a larger breaker for a project where proper sizing of the water heater would eliminate the added expense.

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Actually you forgot to add 125% to the water heater so the load would actually be 46.8 amps.

Redwood said:

Then we get into the scenario of replacing the elements with 3000W elements and both on at the same time which will draw 25 amps... Well the good news is the most houses will not need rewiring for this but your gain is fairly small with only 1500W of added heating power. Thats about 1 Mr. Coffee worth added oomph! Hardly worth the effort.

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Same as above, 125%, so now you do have to rewire because your at 31.25 amps...

Redwood said:

Size the water heater right and maintain it. The engineers really did get it right.

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I could not agree more...

Same as above, 125%, so now you do have to rewire because your at 31.25 amps...

Why would you make that calculation? 6000 watts of elements is always 6000 watts. In what condition does it draw an added 25%?

The function of the top element is to extend the last bit of hot water available and make a small amount immediately available for use rapidly after depletion

water heated anywhere in the tank immediately rises to the top, so I have always failed to see the logic in that old theory.

What would be the point in rewiring one for two smaller elements? If you do that, you have not increased the efficiency or recovery of the heater, and you DO need to replace the lower thermostat with one that has an ECO device.

Again, I see a big difference of calcium buildup on the lower wattage elements, especially if "low watt density" i.e. longer units. They don't boil water on the element. You DO increase recovery by that 1500 watts, and can control it all from the top thermostat and over temp shutoff.

On the other side of things, I needed a shop water heater, and didnt want to run wire. Used an old dual 4500 watter and simply nutted on a 120 volt power cord and plugged it in the wall. Thats a very slow recovery unit, but does the job. If I recall, I tested the draw at about 8 amps. For low useage areas its a easy and wiring free solution.

The manufacturers want you to buy two units or one 100 gallon rig instead of simply wiring it for 2- 5000w elements, thus saving perhaps 3 to 500 bucks.

Electric water heaters have a lot of options if you have an imagination and abide by a few safety rules.

Thanks

I want to thank everyone, for all of the great feed back on my, “158th.stupid questionâ€. I never thought that I would get this much helpful feed back on this post.
Like it was said before, substituting two 3000 watt elements, for the two 4500 watt elements, and running them together, I realized that it’s not that much of an increase in performance, (the Mr. Coffee increase…loved it), but here in Phoenix where you can almost walk on the water, it so hard, I was excited to hear that the calcium wouldn’t build up, (as much) as on the 4500 watt elements. Everyone knows that hot water tanks should be cleaned out at least once a year but, (as I know too well being a handyman) how often does that really happen?
There are families out there that do use a lot of hot water, (more then normal) and they didn’t get the opportunity to size the water heater on the house they purchased from a prior owner. That is why I thought that a modification of the, “one element at a time†might be beneficial.
Just as a warning…my next dumb questions will be, what does ECO stand for, and why is gas pressure measured in, “water column†and not just straight PSI.

Thanks again all!!!

Mike

Raucina said:

Same as above, 125%, so now you do have to rewire because your at 31.25 amps...

Why would you make that calculation? 6000 watts of elements is always 6000 watts. In what condition does it draw an added 25%?

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NEC Code, but dont worry its over rated anyways...

You aren't supposed to load a circuit to more than 80%, so to find out what 100% is, you have to add 20/80 or 25%.

jadnashua said:

You aren't supposed to load a circuit to more than 80%, so to find out what 100% is, you have to add 20/80 or 25%.

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You got a code section that prevents you from using 100% of a breaker? You can certainly load a breaker to 100%...

The code I am referring to is 422.13 Storage-Type Water Heaters

Here's what I don't understand about electrics:

Assume the bottom element is 4500 watts and does most of the work. It's 100% effecient. 4500W = ~15400 BTU.

A 40 gallon gas heater is what, 36000 BTU? At .6 efficient, we're looking at 21600 BTU, or 40% more heat than an electric.

Are electrics just that small because of difficulty in getting more power draw, or what?

Chris75 said:

You got a code section that prevents you from using 100% of a breaker? You can certainly load a breaker to 100%...

The code I am referring to is 422.13 Storage-Type Water Heaters

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It's late, so I'm going to ask it....are you saying that per the code, “422.13 Storage-Type Water Heaters†you can go up to 100% of the breaker rating?