What are the problems with hacking a water heater to run both 240 volt heater elements at once?
Posted on | December 10, 2011 | 5 Comments
I have a 240 volt water heater, it’s rated 4500 watts total with two heating elements.
It’s a brand new tank that was professionally installed but with 6 people in the house and laundry it was running out too quickly. We don’t have room for a bigger tank, and didn’t want a demand water heater since it wouldn’t keep up with two bathrooms.
Both elements are rated for 4500 watts, but it will not run at the 9000 total possible watts due to the master thermostat that regulates the bottom element and kills the power to it (as it should) when the hot water dwindles.
I wanted to know what the possible problems are with modifying it so that there are 2 separate circuits feeding the water tank. Specifically, I have bypassed the main thermostat for the bottom feed so that there is a proper locking romex 3/8″ wire screw down holding it in and wired directly to the lower thermostat. I have removed the pre-existing wires that went from the top thermostat to the bottom.
Effectively what I have done is make it so that both of the thermostats, top and bottom, are running independent circuits with their own separate 12 gauge, 20 amp, 240 volt circuit.
It cranks out a TON of hot water now and is verified as running at 9kw.
It shuts off when it should, no spillage out the pressure relief valve at the top.
What are the problems with doing this from a safety standpoint? The wiring has been secured properly, I’m really wondering if this would cause some pressure issues with the water tank, or create uneven heating, ?? Why don’t they sell them this way? My 40 gallon water tank can run a faucet at a reasonably warm rate non-stop now which is nice, and exactly what I wanted. It doesn’t have the problems associated with a tankless water heater from what I’ve noticed.
Thank you for your response! Some more info: So far it hasn’t overheated the water at all. Each element is an independent heating source (they are not linked) so the top element isn’t going to “overheat” the top column of the water just because the bottom element is turned on. The top element only comes on once the tank has gotten enough cool water there to reach it. Also, I did turn the tank down to the lowest recommended setting just in case it “over-shot” the heating mark.
These are 4500 watt (factory installed) elements. They are on separate fuses with 0 problems so far. thanks for the background with the restaurant industry.
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Tags: Both > elements > hacking > Heater > once > Problems > volt > Water
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5 Responses to “What are the problems with hacking a water heater to run both 240 volt heater elements at once?”
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December 10th, 2011 @ 9:48 am
The problem you will have is the elements will burn out faster and your electric bill is going to go up. They are designed in stages during the introduction of cold water as you turn on the faucet for hot you are refilling the tank with cold so what you are doing in over heating the already heated water which can cause injury to small children etc. Electric heaters were never designed to do what you are doing so I believe it will not last long. My advice is make some room for another heater or convert to gas and then problem solved. Good Luck and be careful!
December 10th, 2011 @ 10:11 am
One hell of an electric bill
December 10th, 2011 @ 10:40 am
Your idea is not completely new as many businesses have done this for years, especially restaurants that require high amounts of hot water and choose not to invest in a commercial heater. I’m not advocating doing this, I’m only saying that it has been done many times before. The main problem that I can see with your design is that you have utilized a 20 amp circuit for each element. You failed to mention the wattage of the elements. Most home heater elements are 3800 to 4500 watts. If you have 3800 watt elements, you’re only drawing about 16 amps each which is borderline but OK. If you have 4500 watt elements, you’re drawing about 19 amps which is tempting failure soon. You either need to install smaller wattage elements, 30 amp capacity (#10 instead of #12) circuits along with 30 amp breakers or return to the original design.
December 10th, 2011 @ 11:36 am
It is OK to do this…have both elements on at once and the papers that come with wiring diagrams show the 2 different hookups.
They are shipped with 1 element at a time as homes are wired with a 30amp #10 wire to carry the load and if shipped with 2 elements at once the home would have to have a 45 amp #8 wire circuit
What you have done is a bit off as you have 2 240volt circuits with 20amp breakers and as stated in another reply ..you are so close to the circuit limit and they may trip if on for awhile and really are past the approved limit for percentage of load.
Another factor is by having 2 supplies to a single unit ..someone may turn off 1 breaker marked water heater and go to work on it not realizing that some power is still there from a second source…dangerous and usually not allowed. You should have a tag on water heater stating “feed from 2 separate power circuits” 2 breakers have to be turned off.
December 10th, 2011 @ 12:02 pm
To add to SolidAxel and Ralph Z’s answers.
1) you need a 4 pole 30 amp breaker for safety reasons
2) 30 amp wire (as mentioned)
My feeling is that when the top element reaches temp. it will shut off. Period.
If the bottom element cuts in at the same time, all that will happen is the water rising will cause the top elem. shut off “sooner”. But then I’m not a plumber.
But I do think I’ll try it at my house.
Yes, your electric bill will likely be higher. But then if you had installed a larger heater, your bill would have gone up then also.