DIY on-demand water heater

Concerning the high cost and complexity of the instant hot water heaters...
About 20 years ago I made one out of parts that can be pretty
easily bought for around fifty dollars and it is still going strong...
Essentially it is made out of 1 inch galvanized pipe and T-fittings..
The T fittings allow you to screw in the 1" threaded screw-in type heating
elements into the heater...  On mine I put in a flow switch (that I
got from a surplus place but that could be bought from a plumbing
supplier)  I wired that to a 240 volt contactor large enough to handle
the flow of electricity...  (I got mine out of a junked large air
compressor)...  and I screwed in two heating elements in series into
the one inch pipe... (that added up to give me the wattage that I needed)..
All sort of hard to explain...  but you get the picture I hope..  It doesn't take
up much room and remarkably it is still working well years later..  I had
commercial bought ones before and got tired of replacing expensive little parts
in them (like their heating elements that would burn up if some air got in the line) or
their electronics which seemed to be damaged easily by power surges...  etc..
This thing I have now just won't quit and when it does I can just get
the parts to repair it easily and cheaply...  I don't have the luxury of a really
steaming shower (especially in the winter when the incoming water is
colder) but my power bills for a 3 person household are under
$25/month so I can live with it..

Sounds interesting David;  
I'm not a fan of electric heating but if it works well for you than its a winner!
I have lived with on demand Propane hot water for over 40 years.
Paloma hot water heaters are outstanding! My first lasted 20 years before I replaced it with a larger Paloma (Got Married)
I sold my old smaller one to a fellow in Hawaii for almost what it cost me! He was ecstatic, as the smaller model was no longer made.
That larger Paloma model ph-12 is still on the job. No electricity needed, only maintenance is blowing the dust off the burners once a year and because I have gravity water , a quick clean of the water inlet screen is it!  They just don't have many parts to fail.  
Now the new on demand heaters are a nightmare!  Noisy , need electric power, and have all sorts of electronic parts to fail.  

I thought that was pretty neat too David.

I heard too the new On Demand Electric systems are a nightmare because they draw so much electricity. Some people have older homes only too find out they are drawing 80 amps of their 100 amp service which does not exactly work.

If I am reading it right, you got around that by using regular hot water heater elements, which would have some sacrifice, in that your system would not have super hot, on-demand hot water. The only concerns I would have is it failing provide hot enough water for proper hygiene on washing dishes. If a person hand-washes dishes then they would want it pretty hot to kill bacteria, but a dish washer requires pretty hot water too. In my tiny house I ran into this problem. At first I thought it was because my run from my hot water heater, to my dish washer was too far, but then I tried bumping the heat up on the hot water heater, and it worked as it was supposed too.

I need to make a homemade version of a BoilerMate on my main house, but I was not sure how to wire it in to the PLC of my heating system. I have a Relay Control with Priority so I know it should come out of that of course, but how would that work? Do I need an aquastat, or is a temp sensor enough to get the relay to fire the boiler and circulator? I was never sure, so I never bought a BoilerMate, nor built a homemade version either.

David,  Any chance you could give us a diagram or picture of your system? It sounds quite interesting that I may want to implement. I maintain like 10 electric hot water heater tanks and each time one gets replaced, I scrounge all the working components before recycling the tank. Needless to say over the years, I have lots of used parts that are just collecting dust and would be nice to use them. Thanks!

Here hopefully is a picture of the materials that I bought to make another of my water heaters.  Unfortunately I haven't wired it up yet but here are the parts in the picture to give you a better idea.  The paddle type flow switch will go into another T that I will plumb into the water line and then it will be wired to the contactor which in turn will send power to the two 1" screw-in type heating elements (I will wire them in in parallel instead of in series)...  To my surprise the galvanized 1" pipe and fittings were bought at Rural King for virtually half of what Lowes wanted for them.    The elements are regular screw in type water heater elements.  In my case I use 4500/3380W ones...  As with all on-demand systems the less the flow throught them the hotter the water gets,.. Also the temperature of the water going into them greatly affects the resulting water temperature coming out.  During winter time my showers are not full blast but they are adequate for me.   The long and the short of it is that I have hot water in my bathroom and kitchen and my monthly electric bill is $35 and $20 of it is a "customer charge"...  My water heater has been working fine for over 20 years now.  The parts I bought were to make one for a friend...

Hi David, Thank you again for the description and picture. It looks like a very easy setup. Would also like to see a follow up photo(s) of it installed if you can. 🤩

I don't see a  pressure relief valve any where in the set up? Is one being used? I have an oil fired Toyo instant household hot water heater and have been impressed with its performance.

Hi Travis, I wanted to point out on your comment about water being hot enough to kill bacteria- years ago I was involved in a study for anti-bacterial soap testing, and the research at that time stated that bacteria needed exposure to 120F+ water for 20+ minutes to properly kill. It's why the dishwasher sanitize option heats the hot water even more. So in most cases it seems the only benefit of warm/hot water when washing is to help dissolve grease so it comes off. So I personally wouldn't be too concerned about the water being hot enough for cleaning, just hot enough to dissolve grease or for bathing/shower comfort.

David,  unless I'm calculating incorrectly, two elements at 4800W using 240V would be using 20A each element, yes?  When wiring in parallel, do you just use a single 50A breaker?  Would it work to wire each element separately using 2 circuits each with a 30A breaker?  All of this assuming the correct sizing of the wiring, etc.  

Wow...just...COOL!....(or 'hot', which ever way you want to look at it.).

Edited with the picture below added---it seems like one could mix and match pipe size and elements.  The element below is 24" long and 6000W.  Don't know if a longer element would provide any advantage in this water heating configuration..?

I'm gonna need to build one.

One thought on getting hotter water is to increase the size of the pipe around the heater elements slightly to provide more "dwell" time of the water as it passes the elements. I wish I had time to test that theory. Also, do you insulate the pipes at all? I wonder if you lose much heat that way.

I never put a temperature and pressure relief valve into this setup but agree that in the interest of safety perhaps I should have.  With that in mind it could probably be added easily into the bottom of the system by replacing that 90 degree elbow with a 1" TEE and putting it there.  I have however wired an indicator light into my system so that a light in a receptacle in my bathroom turns on and shines when the heater is on.  This is sort of superfluous in that I can sort of hear the heater's contactor hum (beneath the countertop in the adjoining kitchen) when it is on.  As for a breaker in the system I use a double pole 40 amp 240 volt one and some heavy duty (I think #8 wire to put it all together...
    And to change the subject to perhaps another topic...  My next attempt to simplify my water heating system is to try those on-demand shower heads that are much in use in South America. (go to Ebay and search for "instant, heater, shower head") for examples...   I am considering trying one in a motor home I am fixing for someone...  Should be even cheaper and simpler than the water heater I have described making above.

Thank you for the update David. The place where I'm thinking of trying it first is under the sink in our kitchen that usually takes over a minute to even start to get warm water out of the tap. So instead of it replacing our electric hot water heater, it would supplement it to save on water waste into the septic system.
I've drawn a picture of what you've shown in your photo but also added where a possible second element and flow switch would be located. Is this correct?

Earlier you said " The paddle type flow switch will go into another T that I will plumb into the water line and then it will be wired to the contactor which in turn will send power to the two 1" screw-in type heating elements (I will wire them in in parallel instead of in series)"
Not sure what the "contactor" is? Do you mean the flow switch? Wondering if you could elaborate with a simple wiring schematic. Thanks!

EDIT: Thanks Robert...forgot to add that on. Updated picture.

If it were just me perfect and simple. The addition of a pressure relief valve and heat shield/screen for safety of others would be inexpensive additions in version 2.0.

Gerry,..  Your picture is perfect except that the contactor is missing in it and is a very necessary part of this device. It makes the high amperage current available to the heating elements.  The flow switch is relatively delicate and can only switch a minimal amount of electricity (probably just a few amps)....  It would instantly burn up if you tried to put 40 amps through it...  Instead the flow switch sends its current to the contactor which in turn activates an electromagnet inside of it which makes the actual high amperage connection.  These contactors are used commonly in almost every high amperage situation..., AC, compressors, heaters,.. etc., etc.,  and are inexpensive and easily available.  You have to match it to the voltage and amperage you need,..  In this case it probably should be 240 volts and 40 amps,  Contactors and flow switches are available on the internet.  My latest one (in the picture) is a higher quality one than the one that I have used for these many years,...  (I think that I got it from the Surplus Center for $5 back then0...    An important note here regarding flow switches is that they rate them to switch at different  Gallons per Minute.   You want to be sure to get one that activates at very little flow...  probably at 1 GPM or so,..  Otherwise it won't switch on at the low flow rate going through the pipes...

Thank you for the information David. Juggling quite a few things right now but I think I have enough info to order the parts and pick the rest up at the store.

If your still there David, a few more questions:

1) I purchased all the black pipe needed (instead of galvanized pipe which you used as I didn't think galvanization around drinking water was a great idea) but was wondering about how hot water tanks have an anode rod to help keep the tank from corroding prematurely and how this system doesn't. I know the back pipe is going to rust over time and will need cleaning but will electrolysis be even a bigger issue?

2) I know your design uses a flow switch and a contactor but is it possible to use a thermostat from an electric hot water heater instead (as I have oodles of them kicking around)?
I have seen this sort of design here: diy-instant-hot-water-heater-plans
Any thoughts?  

Black iron will rust, rust will accelerate with fresh oxygen, oxygen will be supplied with every flow of water.
Consistent flow will keep the rust flushed out, extended idle time will promote rust accumulation.
Legionnaires disease is killed at 140 degrees Fahrenheit. Legionnaires is a result of water stagnating in pipes, once introduced it will survive until the heat is raised to adequate temperatures or the system is bleached.
If you care about such things this system is illegal in every state, county, and municipality, that has building codes, no matter how many safety features you add to it, every single regulatory code has verbiage to the effect of: "must be U.L. (or National Testing Laboratory!) listed."
On a practical level as illustrated, if your water has any electrolytes then if a element fails, and leaks current to the water, there is no other ground path except the stream of water over your body, hopefully you are not grounded, or a harsh jolt is the best thing that will happen......

Thank you for the warnings Bill. This is mostly an experiment to satisfy my curiosity rather than something I am going to rely on. It is just for my own personal use so nobody else will need to be affected by it if something doesn't work out. The diagram in the link I gave had a grounding wire attached to the body of the pipe so shock hazard should be eliminated.

Gerry I just saw that you had asked me a question regarding the use of galvanized pipe.  I do think that (at least with my water) the inside of pipes and tanks quickly gets covered with a mineral deposit which should probably lessen the danger of the zinc or whatever is in the galvanized coating....  Bear in mind too that galvanizing has been used in plumbing pipe for over a hundred years,...  And as for lacking an anode in the system bear in mind also that the water in the heater is only hot very infrequently when it is being used.  It is not hot constantly as is the case in the common type of tank water heaters.  and as for using a typical water heater thermostat switch to control this on demand heater I don't think it would be reactive quickly enough to be safe.  There is a lot of heat energy being put into very little water at any time ...  If the water stops flowing and the heat is still being applied it could quickly turn into dangerous steam and blow something,...  I do think that attaching a thermostatic switch to the side of it and using it as a backup to the flow switch would indeed be a good idea...