Electric water heater -- non-simultaneous?

Had a bad lower element in my water heater and noticed that the diagram indicated "non-simultaneous" operation. I'm just a little curious about this scheme. Seems odd to me because the hot water is going to rise to the top of the tank either way, right?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Yes, but you want the water at the top to have the first priority when it comes to being turned on, because that's the water that's going to go out of the tank first. Once that's up to temp, then in non- simultaneous operation, the uppers shuts off and the lower turns on.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Hi Dave:
Yes hot water rises. But the way I understand, see a recent post about this same subject; the top heater under the control of the upper thermostat heats the upper part of the tank first.
When temp. there reaches the preset the upper thermostat operates and flips the connection over to the bottom heater under control of its thermostat.
Heating of the lower water then continues until the whole tank is full of hot water. The lower thermostat then opens and heating stops. This is sometimes referred to as 'Flip-flop' operation. Or, in other words the top thermostat is a 'changeover' type while the bottom is 'on/ off', type. Note 1.
The design principle being that the two heaters are not on simultaneously. Also that even if there is fairly heavy usage of hot water at least the top half of the tank is recovering its temperature before trying to heat the whole tank again!
Notes: From the various (North American 230 volt style) tanks seen and numerous repairs, mainly to 40 US gallon style tanks performed here; 1) It would be possible to use an upper style (changeover type) thermostat as an on/off type in the lower position 'in an emergency. 2) It is possible (by moving one wire) for both heaters to come on each under control of its own thermostat; BUT that doubles the amount of electric current flowing during the heating period, so the wiring and circuit breaker or fuses must safely sized. The 'total' amount of electrcity used, to heat up the same mass of water, will be the same. The advantage being that the tank will 'recover' to preset temperature more quickly.
BTW with your bottom element burnt out; you will only have roughly half the amount (the upper half ) of hot water ready for use. Are you sure it was the lower element? Although it is more usually one of the heaters, not the thermostats, But a dud thermostat can also result in no current reaching the heating element; especially if something under that cover has got wet!
Any help? Cheers.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Thanks for the replies. The "quick recovery" idea makes sense.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
stan wrote:

So that is why the bottom element works harder than the top one. In a low use situation the water at the top of the tank may never cool down and only the bottom element need run.
--
<<//--------------------\>>
Van Chocstraw
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Nope. Bottom goes on first.
Turn on hot water. Hot water exits from the top. Cold water enters bottom. Bottom cools faster. Bottom element comes on. If demand is high and top of tank cools beyond upper thermo min level,     upper element kicks on. When upper element is on, lower gets shut off. When top is satisfied, lower kicks back on until lower thermo is satisfied. Lower and upper then are both off.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Site Timeline

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.