Comments on: Convert your gas hot water tank to electric

By: Rob

Rob — Fri, 30 Sep 2011 07:36:44 +0000

Hi Tallystick,
That should work, but depending on the toaster oven it may not actually have a thermostat. Some simply turn the element on and off at a variable duty cycle which would have essentially the same effect as plugging the element into a timer and running for a fixed amount of time each day. The best solution is to use a programmable thermostat designed for baseboard heaters. They are about $40 and you have to replace the thermistor to get to the right temperature range for hot water. I did this but haven’t posted the instructions yet… so many projects… so little time.

By: Tallystick

Tallystick — Tue, 20 Sep 2011 03:03:36 +0000

Hi Rob, what about using a toaster oven element, along with it’s temperature control? Seems like that could give you temperature regulation fairly easily by reusing the toaster’s thermostat, and the temperature knob.

By: Rob

Rob — Wed, 29 Jun 2011 06:24:45 +0000

Hi Jeff,
Actually, a “proper immersion heater” would not be any more efficient. Whether you heat the air column or heat the water directly, all the energy you put into the element is transferred into the water. It has nowhere else to go. All that changes is the thermal resistance between the element and the water. That means that for a given power input, say 100W, an element in the air column will run hotter than an element in the water. But in either case, putting 100W of electrical power into the element will put 100W of heat into the water so the efficiency is exactly the same.

The main advantage of immersion heating elements is that they can be much smaller to transfer the same power without overheating and melting.

By: Jeff

Jeff — Sat, 02 Apr 2011 01:27:54 +0000

OK thanks Rob.
Just lately I have been able to get some better elements that I don’t need to join.
Your earlier tip about finding elements in dishwashers was a good one, since I had a useless old dishwasher in the shed.
Also got some oven elements, which may be good since less bending is required to straighten them.
(I hope to use them straight with just one bend at one end)
But I have also been able to scrounge a small electric water tank heater.
I will plumb this in a different location, and bulk insulate as you have suggested on this website.
Then I will have a emergency backup tank.
I guess a proper immersion heater would be slightly more efficient, than having the heating element in the air (in the centre column of a gas tank).
Jeff

By: Rob

Rob — Fri, 25 Mar 2011 17:44:21 +0000

Hi Jeff,
Power = voltage*current and with twice the resistance you will get half the current and thus half the power output. So yes, having two elements in series is a good way to reduce the power output, but as you say, it may be a challenge to connect the two elements and insulate the connection. Good luck, and be careful.

By: Rob

Rob — Fri, 25 Mar 2011 17:37:35 +0000

Hi dave,

Most stoves do not actually have a thermostat (they don’t measure element temperature). They just turn the element on and off at a fixed duty cycle. The result is that the element puts out relatively constant power at a particular setting. Using a timer to limit the total energy input into the tank per day is safer. Using a modified programmable thermostat (one originally designed for electric baseboard heaters) is even safer and that is what I do now but it is a bit more work since you have to wire in a different thermistor to the thermostat. One day I will post how to do it.

By: Jeff

Jeff — Wed, 23 Mar 2011 10:22:45 +0000

Thanks for a fantastic and informative article.
My gas line is rusting out and needs replacing now, but it will cost many thousands.
And I hate those gas connection fees (not usage)
I really want to convert to all electric.
We have 240V AC (Australia).
Hopefully the element won’t run too hot.
I was thinking, could you use two elements in series, with the connection between the two elements at the bottom of the tank ? (not sure how to connect and insulate though).
Then it would be a lot easier to bend the element into a one way spiral, and screw one into the other.
I would prefer to have higher resistance and lower power.
Any thoughts on this ?

By: dave

dave — Tue, 22 Mar 2011 03:40:34 +0000

thanx for the great idea,my gas was 326 dollars this month and tommorrow they are shutting my gas off,its just to costly,i have my element and wire,can you use the thermostat switch off the stove,to regulate the heat also,i do have a timer too,so after work im converting mine,thanx again for such a great money saving idea, dave

By: John R

John R — Sat, 26 Feb 2011 05:41:28 +0000

Well I just realized the outlet has to be in the same cabinet to plug in.

Any ideas or suggestions about this are much appreciated. Thanks

By: John R

John R — Sat, 26 Feb 2011 05:39:04 +0000

Thanks for your feedback. If I understand this correctly, the element can be any shape, and goes to the bottom of the tube, the high temperature wire goes through the cover at the top, then connects to the extension cord?

There is no outlet near the WH cabinet, and on other forum they said a breaker should be within a short distance of the WH. Is that right? The breaker box here is outside, on the other side of the house, which seems sufficient to me. But it looks like I’ll need to put in a new outlet next to the cabinet. Should it be inside the cabinet, or would inside the adjacent cabinet be better (other side of the wall, same room, easy access). Do you think it should have a gfci? I was going to put those everywhere, then realized they all drain phantom electricity, so I’m not as in favor of them any more. I have also been wondering about putting the coil in through the bottom.

I’m going to use the element as you have suggested, but still wonder about induction, as a 500 watt induction coil can melt a lump of metal within 1 or 2 minutes, heating much hotter than an electric stove element. Perhaps a 140 watt induction coil would be just right for a WH, and use less electricity than an electric stove element. Also the coil would be cool inside of the tube, and only heat the metal that is holding the water, therefore not have any wearing effect on the tube.

By: Rob

Rob — Sat, 19 Feb 2011 05:46:35 +0000

I don’t have any experience with induction elements to know whether they would work or not, but I can say with certainty that they would not be any more efficient. Any energy released from any kind of element inside the tank has no where to go but into the tank. Power in = power out. Therefore, the efficiency of conversion of electrical power to heat is 100% regardless of the type of element. Improving the heat transfer (ie reducing the thermal resistance) between the element and the water will not affect the efficiency. It will only affect the operating temperature of the element. For example, immersion elements such as those used in commercial electric hot water heaters have great heat transfer since they are in direct contact with the water. However, they are no more efficient than the stove element I used. For a given power input, the stove element will just run hotter.

By: John

John — Fri, 18 Feb 2011 07:21:45 +0000

Your conversion is awesome and is exactly what I’ve been looking for.

Is it possible to use an induction cooker element, for greater efficiency?

By: Rob

Rob — Wed, 29 Dec 2010 23:49:04 +0000

Hi Steve,
You are correct. Two small tanks would dissipate more heat than one large tank, all other factors being equal… ie same temperature, same insulation thickness, same total volume. But in point 5, the temperatures are not equal. I’m suggesting heating just one of the small tanks. The other would only be turned on during times of peak demand (ex when you have house guests). I edited the article to make that clearer. Thanks for the feedback.

By: Steve

Steve — Wed, 29 Dec 2010 21:13:27 +0000

4. “Even an insulated hot water pipe will easily dissipate all its heat to the surroundings in a matter of hours because its surface area to volume ratio is so high. ”

5. “However, larger tanks dissipate more heat because they have a larger surface area.”

Two smaller tanks would have a greater surface area to volume.

By: Rob

Rob — Wed, 29 Dec 2010 09:59:29 +0000

Hi Steve,
Thanks for your vote of confidence. I looked over points 4 and 5, but I don’t see the contradiction. Can you elaborate?

By: Steve

Steve — Wed, 29 Dec 2010 08:36:03 +0000

Reading on this site has been an absolute delight, I can’t tell you how much of a breath of fresh crisp mountain air it has been. I’m giddy with excitement to try out some of your implementations as I may soon be a homeowner. It’s late so I can’t outline it now but I’ve got a wild solar hot water idea I’ll post soon and in the right project comments. My reason for writing right now is to call into question numbers 4 and 5 under “What else can you do to reduce the energy consumption of a hot water tank?” I am hesitant to say you are contradicting yourself because up until now you’ve been so deadly accurate with everything else I’ve read on your site.
I’ve already told at least 5 people about this site and have been raving only mildly so as not to completely scare them off with my enthusiasm.

By: Rob

Rob — Tue, 28 Dec 2010 09:41:41 +0000

Hi Robert, I don’t think it matters too much to the heat transfer whether it contacts the inner walls of the tank or not. However, over time it may wear away the wall or the element as it rubs during thermal expansion/contraction. I don’t know for certain if that will happen within the lifetime of the tank, but it is probably best if the element can slide freely inside the tube. It should not matter if it lightly contacts the wall (ie you don’t need to ensure there is an air gap all the way around).

By: Robert Tapia

Robert Tapia — Wed, 22 Dec 2010 09:19:24 +0000

Thanks Rob,
Would it be a problem if most of the coil of the heating element touched the tube? Should the coil be “barely” touching or not at all in order for it to heat the air better? I noticed the coil I made was slightly bigger in diameter that it was touching the tube.
Thanks for your help.
Robert

By: Rob

Rob — Thu, 16 Dec 2010 08:56:47 +0000

Hi Robert,
I have done another conversion using an oven element. In this case rather than bending it to a spring-like coil, it’s easier to make a long element. The wattage is a bit higher (around 750W) for slightly faster recovery time. There is also a suitable element in most dishwashers, though I haven’t tried one. Note that on average, the power consumption of the heating element in my hot water tank is under 100W, so you could even use a single 100W light bulb as a heating element. The recovery time would be almost 1 full day though, so you would have to constrain your hot water use to once per day and live with luke-warm water most of the time.

By: Robert Tapia

Robert Tapia — Thu, 16 Dec 2010 08:05:53 +0000

Thank you for all your valuable information and responses. If only people got together this way more often to address common challenges…

What could be other alternative “Heating Elements” that may be already available in our homes just in case. Thanks again and more power to you all.

Robert