Welcome back.
 
In this 2nd of three: “Heat Pump Water Heaters”, it’s the author’s hope to explain in simple wordage, what a heat pump water heater is, and how it accomplishes what it does for you. However, first…
 
 
“Location, Location, Location”
 
Pete doesn’t want to pop anyone’s bubble of being able to employ a mass-produced, residential,
heat pump water heater. So, he needs to alert the reader ‘right out’ that these stand-alone* mechanical wonders only operate efficiently in year-round, stable air temperatures. Lower cost models may require between 40-90 degrees F. (4.4-32.2 C.). More expensive units have wider ranges like 37-145 F. AND they require a minimum cubic feet of air space around them. (This figure wavers between individual manufacturers but 1,000 cu. ft. was an accepted standard.)  This could make them a non-choice for some. However, such things as louvered and trimmed (bottoms) doors can ameliorate some concerns for indoor installations. And, engineers design heat pumps providing not only space heat, AC, but hot water also with units remotely installed.  But Pete hopes his article on heat pump water heaters will still prove useful to many readers.
 
 
How It Works
 
With a heat pump (in general) heat is moved from a cold space to a warm space. The author’s plumber friend and mentor Larry Weingarten will tell you: “Think of heat pumps and refrigerators as apparatus that concentrate and move heat from one place to another. A refrigerator extracts heat from its cold interior, making the inside colder yet, and moving that heat into the kitchen.“
 
As the author researched: a heat pump water heater moves heat from ambient air (inside or outside) into the water in its holding tank. Refrigerators depend on compressors and metal tubing to send gases to various places to keep food fresh. Heat pump water heaters also require compressors and tubing to move heat from the ambient air, into the water in the holding tank.
 
In a refrigerated system ambient warm air is ‘pulled’/sent (fan) across refrigerant-filled evaporator coils. These gaseous filled coils ‘pick up’ the heat from the passing air. The slightly heated refrigerant is then ‘sent’ (pumped) via compressor (which raises further the temperature of the refrigerant). This now really hot refrigerant is piped to the outside of the appliance (usually on side or back). The piping here is often ‘finned’ to greatly increase the exposed area. As the refrigerant moves through this exposed tubing, its heat is released back into the ‘air (kitchen).
 
The now much cooler refrigerant, losing more heat, condenses (liquid) and now at a very cold temperature is pumped through the cooling coils surrounding the ‘fridges’ interior, to maintain a cold and/or freeze temperature for the food it houses. As my friend Larry likes to put it: “A refrigerator extracts heat from its cold interior, making the inside colder yet.
 
 
Even Keel
 
As long as these mechanical components behave and stay on the job, our modern-day life ‘leaves a fine wake.”  When the machine (either water heater or refrigerator) stops working for some reason, some of us may actually suffer some levels of agitation. Yours truly, personally, would prefer to lose (for a protracted time) the benefits of his refrigerator than his hot water supply.
 
Unlike the refrigerator, the heat pump water heater is not sending a chilled liquid refrigerant to maintain a ‘cold box’. The heat pump water heater (with its compressor and tubing) moves the heat from surrounding air and infuses it (heat exchange via submerged tubing coils) into the water in its holding tank. Engineers have a term Energy Efficiency. A simplified way of thinking of this is: A process of reducing the amount of energy required to provide products and services*.  The heat pump water heater is providing a service.
 
*In our case it is the producing of convenient hot water. The efficiency of how this is done is referred to as “a co-efficient of performance.”  (COP).  When selecting a heat pump water heater its particular COP is listed. The higher the listed number, the more efficient that appliance is.
 
ENABLERS
 
There are four possible heat source variables a heat pump can operate on. One of them is: air. Most stand-alone residential heat pump water heaters operate on free air. Many homes space-heated and air-conditioned via air heat pumps may also use heat in the ground (geothermal) to accomplish their tasks. Other enablers are water and exhaust gases from various apparatus. These larger units also can add ‘capacity’ in their design to include the serving you of your hot water demands. As you might imagine, these units are complex.   In this article the author is solely concentrating on the residential, air served, stand-alone, electrically powered, holding tank heat pump water heater.  Illus.1.

The Energy Department’s Northwest National Laboratory, teaming up with: A. The Bonneville Power Administration, Portland, Ore.; B. General Electric Corp.; and C. 10 other Northwest Utilities, designed and administered a multi-year test comparing the electrical current draw between standard electrical resistance water heaters and heat pump water heaters. This test was performed at a load (demand power) rate of 90%.
 
In comparing the two types of water heaters the engineers discovered that ninety percent of the Evening Peak Load power could be reduced by eliminating standard electrical resistance water heaters and replacing them with heat pump water heaters. The study included ten weeks of data collected on 250 water heaters. Of these 145 were heat pump water heaters and 86 were standard electrical resistance water heaters. One of the surprising facts that came to light was heat pump water heaters could, on average, operate their water heaters at 60% of what it cost owners of standard electrical resistance water heaters. This is a remarkable cost savings. For the majority of U.S. households heating water is their second most expensive energy expense. Only top loading automatic washing machines use more hot water.
 
Pete the Plumber surmises that the hefty purchase and installation costs of heat pump water heaters are the major cause for the slow growth in popularity (more than the “atmospheric restrictions aforementioned). But it’s not just the upfront costs that are deterrents. Surrounding Space concerns; Size (height of heater); and Noise (of fan/compressor) and Power (electricity supply installed?) are the big factors that must be taken into consideration when weighing the choice of a stand-alone air enabled heat pump water heater.
 
 
Let’s Open the Box
 
In Photo 1 we see a Rheem air heat pump water heater Pete’s contractor friend Eddie M. recently installed on a major remodel. The owners not only wanted major space/architectural modifications but also wanted to ‘get off’ heating water with Natural Gas. So, the heat pump water heater was incorporated into their plan.

If you think the water heater in this picture looks a bit tall compared to the average standard electrical resistance (or gas) it’s not because of choice of camera lens. The heater is 4 to 5 inches taller than the average standard electrical resistance water heater of equivalent holding capacity. (Where an owner can have installed an air heat pump water heater may require some head scratching.)  Luckily those remodeling or creating a new structure encounter far fewer challenges to do so.
 
 The air heat pump water heater Eddie installed was wired for 30 Amperes on 240 Volts. Some makes/models can function on 120 Volts, but recovery times are much longer. Basically, if an owner chose a water heater with a holding tank large enough to provide approximately 16 gallons of desired temp hot water for each inhabitant, in a shower ‘chain’, a longer recovery time might not be as big of an issue.
 
 One factor that does need consideration is the noise associated with operating air heat pump water heaters. (To install one on one side of a not well sound-insulated bedroom wall would not be recommended.)  Builders of additions and new structures can purposely design and create quiet space to moot this concern. A second ‘must remember’ is keeping the air filter (for compressor cooling) clean. (Pet hair to cobwebs to sawdust). (Put up another ‘fridge’ magnet with a reminder?)

In Photo 2 the reader will notice hanging down in the center of the tank is the anode rod. We were introduced to anode rods upstream, in Conundrum. The reader may also recall in Conundrum, Pete the Plumber comparing water heater warranties. One extra anode added 5 years to the warranty. These are important components. (In Larry Weingarten’s book The Water Heater Workbook he shows the reader how to locate, replace and add anode rods to extend the life of installed holding tank water heaters.)  Now look at Photo 2 again. Where is the (single?) anode on this heat pump water heater?  Directly under the compressor!  (Pete would not covet the task of replacing that one.)
 
One worry that owners of standard electrical resistance water heaters and fuel gas water heaters do not have however, is the bother with a condensate drain line.* Heat pump water heaters (via compressor) produce condensation and need to always ‘pipe’ it away using a condensate line (drain line) (most always of easily assembled Schedule 40 PVC pipe and fittings.)  The trick involved with condensate lines is: Always Be Going Down Slope (to a legal final destination). If the plumber cannot arrange this by gravity flow, then a sump and electric pump must be included in a heat pump water heater installation. Don’t panic. There are manufactured such ‘plug-in’ collector/pump combo’s (just for this purpose) available at plumber and or builder suppliers.
 
*This issue of the condensate drain line is really no more fuss than what a conscientious plumber does when installing a gas or standard electrical resistance water heater inside a building:  Install heater in a properly sized drain pan with properly sized drain line, Code sloped to a final 90-degree bend, pointed down, 6 inches above grade (ground).
 
 
A Special Case
 
As mentioned upstream there are atmospheric limitations for air supplied heat pumps in general. It’s no different for heat pump water heaters. More than one manufacturer of air heat pump water heater has ‘the answer’ for the marginally sited: Hybrid air Heat pump water heater. These up-scale models are able to automatically switch back to using the standard electrical resistance heating elements when atmospheric conditions are not co-operating. This may be a game saver for those readers living in Northern latitudes.
 
 
Why?
 
The majority of we Yanks live from paycheck to paycheck. If/when our ‘silent, obedient, hot water servant’ suddenly gives up the ghost, are we going to spend maybe three or more times the money to get our hot water back?  (Even if you’re a Tree Hugger?)  For most of us the answer will be: “No, just don’t have the bucks for a heat pump water heater” (right now). Yours truly believes it will require generous rebates from both manufacturers and Government before we witness significant saturation of this energy saving water heater technology. The author’s upstream stated belief of new construction mandated acceptance will be tested.
 
There’s a hefty haul of information for those who would like to pursue this topic further, on their own. Pete has assembled the following list of inform-able sources on the subject of residential air Heat Pump Water Heaters:  Have fun. Dream.

Further Reading Links:
 
How it Works – Heat Pump Water Heaters:
https://www.energystar.gov/products/water_heaters/high_efficiency_electric_storage_water_heaters/how_it_works
 
The Pros and Cons of Heat Pump Water Heaters:
https://goodbeeplumbinganddrains.com/the-pros-and-cons-of-heat-pump-water-heaters/
 
Living With a Heat Pump Water Heater:
https://www.energyvanguard.com/blog/living-with-a-heat-pump-water-heater/
 
Heat Pump Water Heater Ultimate Guide:
https://sealed.com/resources/heat-pump-water-heater-guide/
 
Heat Pump Water Heaters as Clean-Energy Batteries:
https://www.nrdc.org/bio/pierre-delforge/heat-pump-water-heaters-clean-energy-batteries
 

 Pete will be back sooner than later with the third and final installment in this series. In the meantime, have many readers ‘picked-up’ (media) on major metropolises green lighting the addition of treated sewage water into municipal fresh water supply systems?   That practice might make for some future comments in The Pipe.
 
 
PtP

O.K…the author admits it. He’s been derelict (AWOL) in feeding his article stash. Part of the reason (I know, ‘no excuses soldier!’) was a lull in the author’s topics of interest colliding with his consciousness…, fishing and kayaking suffered not. “A Conundrum”, is this Pipe’s first of 3 installments involving domestic water heaters of/for the future. Your Rip Van Winkle-esk author hopes he can make up for his last spell of laziness? by sparing the reader (in the future) a lot of “head scratching” when ‘must-choosing’ one of 3 sanctioned, electrically powered water heater designs.
 
Why would someone be put in this situation of ‘must choosing a water heater?  Read on…
 
Of late, there was ‘zilch’ in the plumbing realm sufficiently inspiring Pete to nudge you. (He trusts the reader put the same time to good use?)  However/But, the author DID do some wrestling-on-the-couch:  “…..would it behoove the reader to know about some ‘plumbing things’ (politics included) that might prove, in the not-too-distant future, a possible lifestyle ‘upend-er’ for many. This change (the author believes) will involve HOT water. And, how the cold water turns into hot water might interest the reader.
 
Is your fresh water supply heated by using electricity or by burning natural gas or propane?  This question is the seed of Pete’s story. (“Oil-ers’ are excused from class.)
 
Because climate change is forcing human activities to become as *environmentally clean as we can do them, staying clean via hot water (using some form of heat energy) will not escape closer and closer inspection.
 
 
The Big 3
 
Today, three concerns of geo conservationists are causing elected officials to fret over continued use of fuel gas (Natural Gas and Liquid Petroleum Gas (Propane) to fuel stoves. Concern 1. Radiation in Natural Gas includes uranium and thorium.  2. Stanford University researchers discovered using gas stoves raises indoor levels of the carcinogen benzene to higher levels than secondhand tobacco smoke.
3. Global Warming concerns include methane (mother of natural gas) leakage in the oil & gas exploration and production. And, additional concerns involve air-pollution, possible asphyxiation and fires.
 
Presently gas stoves are the ‘hot’ target. (Yes. That was a pun.). But, the author thinks gas water heaters and furnaces won’t be that far behind. He expects only a grace period (once stoves have been banned) before we see legislation aimed at them.
 
 
Hot Nuts and Bolts
 
Because the topic of hot water heaters can encompass so many technical aspects, the author wants to narrow his focus to the why of this article: There’s a chance that in the future, in enough parts of the Country, Natural Gas (due to health concerns) (and a little politics) will be phased out and *electricity will be tasked with making/facilitating all the domestic hot water. Those readers presently being served hot water made with electricity will not be affected. Those making hot water by Natural Gas/Propane will have to purchase a new, electric water heater.  Of course those readers who use oil/kerosene will not be affected.
 
*Suburban dwellers relying on well pumps still need electricity (whether it be by solar or Utility), to live ‘on solar’.
 
Dive In
 
Pete the Plumber would now (in 3 Installments) like to describe and illustrate 3 popular designs of electric holding tank water heaters on the American market, today, and tell you their advantages and shortcomings. The author did not include “tankless” water heaters in this discussion because he admit-tingly has a bias, born of decades of experience. He is not a fan.
 
 
The Line-Up
 
Pete perceives 3 possible/probable ‘camps’ of questioning among the readership for this article on holding tank electric water heaters.
Camp 1. Bored-to-curious. Moot.
Camp 2. Individuals needing to replace an existing mass-produced water heater. (This could mean replacing a simple electric heater with another like it, OR replacing a gas water heater with an electric one.)
Camp 3. Individuals interested in 2 higher technological choices for a holding tank electric water heater either for replacement or new construction. *
 
*Pete thinks this new construction will be the arena where the political battles of banning the use of gas home appliances will find eventual traction.
 
 
You’re Busted
 
O.K. Assuming the worst. Let’s say (in the future) one or more of my readers were informed that they need a new water heater. And…the County has successfully banned all new gas appliances. What would then go into the decision to choose an electric water heater?
 
Those readers presently served by an electrically heated hot water appliance wouldn’t feel the crush like the ‘gas-ers’ will, when/whenever fossil fuel hook-ups are banned for all new construction. And with a possible quick sunset on existing installations. Today’s basic tech level, mass produced holding tank electric water heaters could simply replace a worn out one. For an unfortunate “gas’er” how and what their choices are, are thoroughly discussed in the trio.
 
 
Confession
 
Yours truly was raised in homes with natural gas stoves and furnaces. He and wife, Katherine, also raised four children in a house with a gas stove and gas furnace. As a result, the author prefers gas cooking appliances over electric ones but understands the rationale for retiring the ‘blue flame’.  
 
In some parts of the Country (especially mountainous and/or remote), fuel oil/kerosene can figure into the equation. Which energy gives the reader hot water?  Yours truly has loved ones living in the ‘far flung’ whose homes and fresh water are heated by appliances burning fuel oil. This article will not discuss the merits or de-merits of fuel oil.
  
For all dwellers presently living in communities served by NG gas, with a future total ban successfully implemented, those hot showers the reader is presently enjoying are going to have to originate in an electrical or solar water heating appliance. This spells considerable expense, and the author hopes this article will aid them in choosing the ‘right’ hot water servant for their needs and budget.
 
 
Factoids
 
The number of ‘gas’ holding tank water heaters versus the number of electric holding tank water heaters manufactured today (2023) is approximately 50/50.
 
There are three major American water heater manufacturers: A.O. Smith; Bradford White; and Rheem. Between these majors and a few independents there are hundreds of different brand names on the market. It’s not unlike the food canning business. One cannery might produce the same can of peaches with twenty different labels.
 
 
Hot Oil
 
As mentioned above many readers may be employing “oil” for heating needs, both water and space. The author has a friend, Becky B., living in a mountainous location in his State who cooks with electricity, heats water with an oil-fired water heater and space heats with propane. Sometimes when living in extreme weather locations where electrical utilities routinely suffer outages it can pay not to ‘put all your eggs in one basket’. The author feels that this “out there” group may/should be the last ‘made’ to make ‘changes.’
  
For the rest of us living in gentle climes and hospitable topographies, and perhaps already employing (or with an option to) an electric water heating appliance, and whose life/styles are not at risk of bans, Pete’s piece also has some information you might find of some interest. (And possibly some money saving in the future). For our poor ‘gas-ers’, this article is more focused on your having (at some future date) to choose an electric water heating apparatus.
 
Just for the record, the author resides in a living space surrounded by steep, heavily forested terrain. Because of heavy snowfall and high winds, the electrical utility serving Pete’s abode can be expected to lose power, winter and summer. (And now and then for an extended period). Pete’s neighbors have electric water heaters. Pete has an LPG (propane) fired holding tank water heater. With extended power ‘outs’ the author’s unwavering hot showers are a source of considerable neighborhood want.
 
Pete’s electric water heater ‘stories’ begin with a basic (graphics supported) description of today’s economically priced, electrical element, mass produced, steel holding tank water heater. And how it works. The author reckons this basic, lowest cost (electric) water heater will be around for some time to come. Two other described designs of electric holding tank water heater the author considers advanced and are ‘expensive’, relatively, will also be discussed. But, Pete’s suspicion: at some point in the future, one of the advanced choices, the heat pump hot water heater may become the mandated design in all new construction and replacements where physics and weather allow. Were this to happen (politics) the reader might have no choice but to install the expensive, technologically advanced heat pump water heater. That is why it is included in this Pipe.
 
As was with toilets, when super efficiency models became available many communities’ Water Utilities gave rebates that enabled many customers to afford swapping their old water wasting designs for the new, super low-flow models. Pete believes similar programs will be made available for advanced/more efficient water heaters, when “push comes to shove”)
 
 
An Outlier
 
In the third tale-in-line for this Pipe, the author describes an advanced version of the ‘basic’ holding tank electric water heater with a lifetime warrantee, for those readers who today or in the future will be staying put in their homes for “the duration” and who need or want a new water heater. This heater is the Rheem Marathon, a fiberglass tank version (with no need for dielectric anode rods, as discussed, following). You could bequeath this Rheem water heater to your children.
 
But, before spending time talking the advanced models, let’s dissect, as promised, the ‘long-on-the-job’, basic, 30 to 50 gallon, steel tank, electric, holding-tank, residential water heater.
 
 
Wrapped In Blue
 
Ever wonder what factor most threatens the common ‘holding’, steel tank, water heater?  (Yacht owners already know.)  Aggressive Water is the culprit. When fresh water is heated to high temperatures, it starts behaving badly. (Like it’s meaner sister, salt water.)  It’s molecular ‘arrangements’ play musical chairs, and someone always loses. The water is then ‘hungry’ for molecules it no longer owns. This is now aggressive water. It’s going to fight to get back what it lost.
 
It just so happens that the steel walls of the tank suffice as nutrient for the aggressive water. Over time aggressive hot water can eat all the way through the walls, floor, or the top of the tank. Major Leak time. Catastrophic, National, property damage results annually.
 
 
Davy Jone’s Salvation
 
For the yachtsman, clamp-on zinc shapes are placed on the hulls underwater metal components, to protect them from ‘being eaten’ (while they are submerged). These added shapes sacrifice themselves to the hungry aggressive water for the sake of the hull. (And need to be replaced cyclically.) To protect the steel tank of the water heater from heated fresh water, its interior is coated with a layer of vitreous (molten) (mucho hot) glass, many times dyed blue,  
 
Somewhat like the saltwater yachtsman protecting their hull with zinc, water heater makers introduce ‘sacrificial’ metal rods (anode’s) into their tanks. These (preferably) magnesium rod forms are replaceable, usually by un-threading them where they were installed. (Sometimes tricky to find where). As the rod is eaten by aggressive water, all’s well. When it’s totally consumed, the aggressive water goes on the warpath and looks at any ‘soft defenses’ in the vitreous tank lining protecting the steel of the tank. The aggressive water likes the steel underneath almost as much as it likes the factory installed magnesium anode rod. As long as the anode is replaced ‘in time’, the heaters life can be extended considerably.
 
Moons ago the advertising of one competing water heater manufacturer claimed it gave their tanks a ‘Second Coat’ of ‘…Glass Lining…’.   When and how (in the manufacturing process) does the steel tank get this glass coating?  The tank was complete when molten glass was ‘sprayed’ through existing threaded holes. If the apparatus that applies the molten glass fails to maintain its precision and ‘misses’ or only ‘lightly’ applies the vitreous in one spot or two, that leaves the tank vulnerable to early failure. So, some savvy manufacturer, in their ads, claimed it performed a ‘second coating’. The most thorough job of applying the glass could mean a longer-lived tank. To this day, when I watch my friend Larry the Plumber (larryweingarten.com) use a sawz-all and perform a water heater autopsy for his plumbing class, the inner tanks are often blue (like us?)
  
Pete’s good friend and mentor, plumber Larry Weingarten, has written a ‘home run’ of a manual showing in easy to understand text and illustrations) how to care for and repair the basic water heaters. His website is: larryweingarten.com. Here you can order a copy, and the curious can also enter Larry’s amazing on-line world of hot water.


Dive In
 
O.K., Illus. 1 is the theoretical, standing -‘half’ of the modern day, residential electric water heater. 

​Steel tanks are made by rolling flat sheets of steel into a desired diameter, forming a tube, and then seam welded. The concave top is a separate piece, stamped or spun, and welded to the tube. On it are threaded openings, usually three or four, depending upon model. #3 The Cold Inlet /dip tube; #1 Hot Outlet tube; #2 the magnesium Anode Rod and possibly a last one for T&P.
 
Our tank (the ‘Yellowstone’) has the T&P on the upper side, left.  #7.  
 
The tank bottom is also a separate part, welded to the tube. Welded to the tank bottom is its base, another separate part.
 
The walls of the tank will host its own share of holes. Two are for the thread in electrodes #4 & 5. Another is for the T&P Valve (temperature and pressure relief device) #7.  #6 Is the threaded hole for the tanks drain valve.
 
Some water heater’s (depending upon the make and model) will have two extra threaded holes on the side of the heater for cold water-in and hot water-out.  This is a tremendous help when the heater needs to be placed in tight quarters. Needless to say, it is a luxury paid for. Equally beneficial is the manufacturer who provides 2 possible locations for the T&P Valve.
 
The fuse protected electrical power cable #9 in our illustration brings 220 Volts and (in our case) 30 amperes of electrical power to the two thermostatic controls, #10 & 11.
 
*Unlike thermostatic controls on gas powered water heaters, with a built-in, multi-inch probe, the thermostatic controls on electric water heaters #10 & 11 are flat and mount to a flattened surface on the tanks outside wall. Electrical wiring connects the two thermostats to the two thread-in electrical resistance heating elements #4 & 5.
 
 
The Ins and Outs
 
Cold water enters the tank through #5 the blue dip-tube. Notice the tube hangs down into the tank a long way. It’s that long because designers of the water heater want incoming cold water introduced near the bottom of the tank. (Cold water is ‘heavier’ than hot water.)  About the upper 1/3rd. of the tank holds the ‘desirable/useable’ amount of heated water in a cycle. It would not be a good idea to let cold water dilute the temperature of the existing hot water. This would happen if not for the cold-water dip tube.
 
What else ‘hangs down’ from the top of the tank?  Components #1 & 2.   Number One (Red) is the hot-out tube. Number Two (White-ish) is the magnesium anode rod. *
 
*Pete has a confession. The anode rod as drawn is about one-half the length it would be.
 
The red, hot-outlet tube is much shorter than the blue cold inlet-tube, as one can see. And for a good reason. The longer the tube length is, the cooler the water it will be tapping. Some smart people are the reason lengths are ‘what they be’.
 
 
Recycle
 
The author thinks/hopes the reader is game to witness a full cycle operation of the modern (electric) two electrical element, holding tank water heater. As mentioned upstream about one-half of the water heaters operating in the U.S. are this type.
 
Let’s pretend your domicile makes its hot water with a facsimile of the water heater in Illus. 1. And, it’s early A.M. and you get outta bed and head for the shower. Uh Oh. No hot water!!!!  (Not a good way to start the day). The heater is eventually (hopefully timely) replaced with a new one. And it is filled with COLD water on its first filling. Then the power is turned on. What happens next?  The water heater’s upper e.element (green) #4 is energized. The work performed by the upper e. element heats the water at its level (height) and above, to the set temperature on the thermostat. As the water temperature reaches the setting on the thermostat, power is cut off and it is now sent to the green lower e. element #5.
 
The water at this lower level of the tank is now heated to the temperature set on the lower thermostat. With this accomplished, the water heater is now at rest and waiting to serve.
 
  
Crossed fingers
 
A theoretical Someone (again) takes a shower. (This water heater has resting hot water.)  By opening the hot port of the shower valve, cold water starts entering the heater (through the dip tube) #3 to the bottom of the tank. The lower thermostat feels it and and sends power to the lower e. element, #11. All this while the therapy of enjoying a hot shower is happening. With the shower valve turned off the reader is now energized!
 
O.K./ However, if someone else takes another shower right away, the top thermostat #10 will send power to #4 the upper e.element. ONLY ONE Electrical. ELEMENT IS POWERED AT A TIME.
 
If the water heater’s tank is ‘sized’* correctly, about 90% of the heating will be accomplished by the lower e.element. The Department of Energy has an easy to follow guide to sizing a water heater. You can find it at: https://www.energy.gov/energy saver/sizing-new-water-heater
 
 
A Little, side-History
 
When Pete the Plumber was an apprentice in the late 50’s, water heaters were widely available in four warranties. The first was a 5 yr. warranty with a caveat or two. Next was a 10 yr.  Third choice was a 15-year warranty and 4th and last, you could get a 20 yr. warranty. Today?  No longer.  *caveat
 
*The author does, though, in the 3rd. discussion involving the Marathon water heater, ‘talk’ you through the construction of this Lifetime Warranty electrical, fiberglass holding tank water heater. It’s his choice and he will tell you why.  (Admittedly it is priced for those ‘staying in place’.)
 
Back to the reasons for the discrepancies (then) in the water heater warranties. These included: tank wall thickness; glass glazing: coats/thickness; number of anodes; number of female iron pipe ports; thickness (and type) of thermal insulation and quality level of heat producing/regulating source. Today, because of Larry Weingarten’s book: The Water Heater Workbook, the reader can ‘assemble’ their own 20 yr. (or more) hot water servant. (Every shower thereafter renews your DIY pride.)
 
 
Spit It Out
 
Because the cost of initial purchase and/or replacement of any holding tank water heater is what it is, a sane person would prefer not to be subjected to it for as long as possible. (It’s a shame that all manufacturers (both gas & electric) are guilty of ‘short-circuiting’ your chances of a long-lived water heater by supplying an inferior drain valve (orange) #6. See: The Water Heater Workbook.
 
 
Though this Pipe was intended as a comparative study, repairing water heaters is too large of a topic to include. However, the reader faced with a water heater replacement or repair would be wise to own a copy of Larry’s book.
 
At/with the final word of “Conundrum” a coffee/tea break is recommended. For those who didn’t perish on this rocky word journey, Pete hopes to ‘see’ you jump in, slide, or fall into “Heat Pump Water Heater’s”, following.