Plumbing in the Home/hot water heater


Hi Cort,
The situation is a residential electric water heater, 50 gallons, General Electric   model SE50m12AAH. To save money I put it on a countdown timer so we only heat the water when we’re going to use it. The settings on the timer in minutes are 10, 20, 30, 60, and hold.

The shower head is 1.6 gallons per minute.

The water is usually running for about 10 to 15 minutes for one shower and the other usually takes 5 to 10 minutes.

M – F there is no problem, the first shower heats for 30 minutes and the second shower heats for 20 minutes about 2 to 3 hours after the first.

On the weekends we are in habit of taking a shower one right after the other without shutting off the water. Logic states 30m plus 20m equals 50 minutes. So we tried the timer on 60m and the second shower ran out of hot water. Then we tried stopping the shower for 5m between showers and that was worse.
Last weekend we tried 60m, then when the first person started the shower we started the timer at 30m and the second shower ran out of hot water.

So, closer to the point, I would like to understand how water flows in an electric hot water tank. Is it first in – cold water, last out – hot water, or is it just a 50gal drum?
I’m trying to find the solution to save money and not run the electric longer than I need to, but also take a comfortable shower without running out of hot water. I’m all for saving money, but not at the expense of comfort.
We live in a cold climate, 4 seasons, but winter’s average is usually below freezing.

Any ideas?
Thank you,

cutaway view Electric Water Heater
cutaway view Electric  
Hi Randy,
You are on the right track and it is all math and compensation for your weather situation…do as much insulating of the lines as you can, both hot and cold at the heater should be insulated … heated water will back up in the cold line at least five feet depending on the pipe layout. Insulate as much as you can is going to help some…
This cut-away view should help. Fortunately you have an upright style heater so you can accomplish what you are attempting. I say upright as compared to the ‘stubby’ style which is only half the height as the upright but much larger circumference and that would make it difficult to get the separation you need between the layers of heated water.

This is the image URL of the cutaway. <a href="">

The cold water inlet has a dip tube (this is the name commonly used ‘dip-tube’)  This tube conveys the cold water entering the tank to the bottom area of the tank; the purpose is to pass through the heated water which will always rise to the top as water becomes less dense as it is heated thus it rises just as hot air rises.

The 50- gallon heater is a bit large for what you are doing but it will work okay as long as you have a good handle on the theory and management. Basically you are not going to use the lower element very often it seems and if only two of you are consuming water a smaller heater might be more practical but that aside you (with the patience and persistence) can achieve what you are wanting…

I assume you are pretty mechanical; to work on the electric elements and thermostats you should be somewhat knowledgeable…BE SURE TO TURN THE POWER OFF WHEN WORKING ON THE WIRING AT ANY TIME…..
You should refer to your heaters wiring diagrams and most electric heaters will heat with the top element only until a set temperature is reached within the tank then the power switches to the bottom element…you may be able to achieve your goal by using a higher wattage element in the top/upper position but that is another calculation you must make…
Use this URL: < href=">

If you do not have all the specifications for your heater…if this is not the correct URL you should be able to find it there…

Just visualize what you are doing and do the math and you can make it happen …one caveat is that these dip tubes are thin plastic and sometimes fail by splitting or breaking off…this causes cold water to enter the upper space of the heater and ruins all efficiency and if that happens you may not get any or at best very little heated water. This condition merely requires a new dip tube and while that is normally an easy fix it can be a problem if there is no head room where your heater is located and in that case you often have to drain the heater in order to replace the dip tube…this is not a real high probability but it does happen…

Good Luck, cort  

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Cortez (cort) Cate


PLEASE read this entire introduction. I have been doing this for a long time and I have come to the conclusion that if you are not willing to take the time to write a detailed question then don't expect a detailed solution! I am getting far to many questions that do not give enough detail to warrant a good solution. I realize it is a little difficult to formulate a good question but if you want a good answer you have to give me good this entire introduction please....remember this website is world wide I have no clue where you live if you don't tell give more detail on the fixture you are having problems with...a one piece eljer 3.5 gallon flush will be totally different than a one-gallon flush toto.....details are important. I can answer most questions related to residential and commercial plumbing for many buildings. I have sufficient knowledge of the UPC and UMC. I will speculate for you if necessary. In those cases I will try to give you some guidance and you should use that to refine the question further and we, together, can seek the answer via a follow up. Plumbing codes and practices vary around the world--If you don't tell me where you live the answer I give may not fit your locality. I am giving my time to you as a way of fulfilling my perceived obligation to share. I am here to try to help you find a solution to your problem. REMEMBER, If you want a good answer you need to ask a detailed question and include where you live, type of pipes, type of building, water pressure if it is a water problem, type of heater, age of appliance & building all these and many more are variables that have an effect on various situations. Detailed information will help produce a better answer.


Since 1972 a California licensed B-1 General Building Contractor, C-36 Plumbing and C-16 Fire Sprinkler Contractor; also installing and servicing Heating, Air Conditioning and Sheet Metal operating as C and C Building and Plumbing, California State License 279516. In 1995 I downsized the company to become semi-retired. Still I remain active in the construction industry. As head of a company I placed personnel and job safety as the number one objective followed closely by training and continuing education. Always seeking to stay informed of leading edge technology in the industry. Also I have spent several years as an Apprenticeship Instructor in the Pipe Trades Unions. Additionally I am a certified OSHA instructor.

United Association of Plumbers and Steamfitters Instruction Training, Ann Arbor, MI Bakersfield College, Bakersfield CA Cal Poly San Luis Obispo, San Luis Obispo, CA Foothill College, Los Altos, CA California Licensed Contractor from 1971

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