Steibel Eltron conducted a test that compared the cost of heating water using a conventional electric geyser to a gas geyser.
They have kindly allowed us to publish their test.
Test Methodology
A 100 litre electric geyser was mounted right next to a gas geyser on an outside wall above a 100 litre drum. The electric geyser was emptied into the drum twice a day, once in the morning, once in the evening. The drum was filled with hot water from the gas geyser also twice a day, at about the same times.
In this way the same amount of water was heated using each different method, using the same inlet water, at about the same times every day for a month.
This was done every day for a month and the costs compared.
Both systems were set to heat water to 55C, and both used the same inlet water.
The geyser operated normally, without a timer.
The gas bottle was only opened for each test run to eliminate any potential excess gas consumption caused by leaks.
Results
Electricity tariff during the test – R1.22/kWh
The gas used was from a 45 kg cylinder which cost R 1,070.00 (incl. VAT). This equates to a rate of R23.78/kg.
Using those prices, the cost of heating the water for each method during duration of the test was:
Electric geyser – R 469.70
Gas geyser – R 502.21
For more information about this test please download the detailed test document or visit their website.
Honestly, the result was something I would have expected though I’m still glad to know somebody actually cared to make experiment to prove this in an objective manner. The gas used here has got to be propane gas and in most parts of the world, its cost per unit energy is close to electric and sometimes so close as to make electric a more economic choice. As for the geysers, electric geysers are always 100% efficient but even the most efficient gas geyser ever cannot be more efficient than 90%. Some heat is inevitably wasted in the steam that goes away as hot fume.
In no way, is an heating device 100% efficient, and never will an electric geyser be 100% efficient. You can try, but will not insulate a geyser completely. Water resting in a pipe between tap and geyser (where hot awaits) need to flow out, the cold water down the drain until you get hot, is lost. Dissipation from the geyser body and surrounding piped, even if insulated = Loss. Constant trickle heating to maintain set temperature, loss. Gas does not have that requirement, but does have the same other losses (cold water in the pipes, possible leaks, etc).
I think a fully scientific (but real world) test would reveal MUCH lower percentages of efficacy on both systems.
But the test here is pretty good, and better than most of us will attempt, and the numbers in final costs makes sense. Probably due to the fact that gas is a petroluem derived product, and we pay by the wet-van-transvaal for all of these 🙁
The test might seem logical, but it is not. In a real world application, the electric geyser has to keep all the water hot 24 hours a day and heat all cold water added due to usage, irrespective whether it will be used or not. The gas geyser does not have to heat 100 liters of water, as it only heats the water you actually use while you shower of for your bath.
Your experiment is correct, but irrelevant.
The results seem to speak for themselves?
It costs less to use a normal geyser, than to instantaneously heat water as you use it with gas.
Surely that’s relevant?
Your test methodology may be slightly lacking. The main problem with an electric geyser is that it is constantly heating up and cooling down. in a normal household you would rarely empty a geyser. What you have proved is that to heat up 100l of water an electric geyser is more cost efficient(based on the price you paid houses with gas lines would probably pay less).
If you were to repeat this type of test one would need to perhaps try only emptying smaller amounts of water at a time. say calculate the amount of water used in a shower or bath and maybe use 2 of them a day with a smaller amounts for general hand washing through out a day.
All in all these experiments are interesting thanks for adding
Nowhere was it mentioned that the Electric Geyser was switched off during the times it was not used? It stated that it regulates itself normally, without a timer, which means it was constantly switched on and had to produce 2*100litres of water daily, same as the gas.
My thoughts on reading the test methodology exactly, fundamentally flawed for real world scenario
Can’t disagree with the figures but would rather see the test done as follows:
Rather say a person showers in 40 deg C water then use a fixed mixing valve to supply the 100 liters of water at 40 deg C. What will the readings then be?
Get rid of the manometer. The gas geyser will use the gas as required. You calculated the gas used by weighing the gas cylinder.
By the way. How did you make sure that the water stayed at 55 deg C?
I pay R 18.11 per kg for gas VS R 23.78, same test would have cost R 382.49
The problem is not the cost. It is that EKSDOM will turn power off `whenever they feel like it and then ANY alternative to electricity is a bonus. At one point we were without water for 3 days and we had load shedding every day. I used my Borehole to fill a tank and used gas to cook and shower.
We will see more and more water outages and power outages and if we do not move to alternatives we will be screwed.
Not only that, what they have neglected to mention is that the more water you use the more electricity you will be using, like wise with gas, the more water the more gas, the difference is that with eskom, the more electricity you use the higher the rate escalates whereas with gas it does not matter how much gas you use you will still pay a constant price per kg, it would just have to be managed like prepaid electricity, having to buy your gas in advance.
Enzo
I pay about 200 ronts for a 9kg bottle so 20 something per kilo
At 11 rand per kilo thats a good deal
Where do you buy the gas from ?
Bones
I get buy gas from Gas2U in Bapsfontuin, 163 for 9 kg, they have a special this month for 136 for a 9 kg.
I agree with Ama how can you compare if you are switching the electric geyser of as in any normal home a electric geyser is on 24 ours a day and not just for warming wen you need it. As a mater of fact you can’t just turn it on and it heats it takes a long time for the water to heat but with the Gas it’s instant.
They specifically mentioned that the geyser was operated normally without a timer, which means that it would keep its temperature constantly and reheat the contents twice a day after use. I don’t see what was unclear.
Gas Prices R18,77 per Kilo (Gov regulated). The Price of the the Electricity can be debated on: A typical house uses around 800 units a month, using Home power 1 tarriff the would take you bill to around R1301.18 including daily network demand fees. That means the average real unit cost is R1.62. Therefore using your experiment data: Gas = R396.40 and Electric = R623.70
Gas seems to be the clear winner.
I did the test. A normal 150 l geyser costs R600 a month. The benefits of gas. Hot water as long as you have gas. We have a Rinnai 26 for three bathrooms and a 10l cadac for the rest. Its about convenience not price. Andre Venter
Ama`s response(2nd): the geyser operates UNDER NORMAL CONDITIONS WITHOUT A TIMER–see test conditions, thus making this test RELEVANT.
I also did some calculations of my own. Here are the theoretical parameters that I used:
Ambient (outside) temperature: 15°C
Shower Temperature (setpoint): 42°C (for ease of calculation, max temp for 10l gas Geyser)
Energy loss from geyser (conduction, convection, radiation): 2.5kW/day
20-minute shower/day @10l/min resulting in 200litres per day usage
Geyser setpoint: 70°C
By using the exact same daily amount in a traditional element geyser, taking into account the amount of water that had to be reheated flowing into the geyser, the average daily use of the element geyser was about 363kWh (@ R1.22/kWh it’s about R443/month).
The Gas geyser, 10litre, set at maximum temp of 42°C with same water usage, using approx. 1.55kg LPG/hr, a 20-minute shower resulting in 200 litres per day, it’ll run through 15.5kg/month. For a 48kg gas refill you’ll pay R1036, which means you’ll have to cough up R334/month for gas.
In Summary: R443/month for Element, R334/month for gas. It will all boil down (no pun intended) to the cost of installation of replacing your element unit with gas. With a difference of R109pm, it might take you more than a decade to recover the costs, probably more.
I have a few issues with Steibel Eltrons’ experiment:
– They never specified what the rating of the gas geyser is. There’s a huge difference in gas consumption between an 10litre and 16litre gas geyser, the former of which is sufficient, borderline overkill even, for a decent shower.
– The operating conditions are not feasible in my opinion: Although it might be a bit optimistic to use an inlet temperature of 20°C (@6a.m.?), the outlet temperature for a gas geyser is ridiculous. Yes, you may want to set your Element geyser to a higher-than-tolerable temperature, which is why I used 70°C for my calculations, but running a gas geyser at 55°C will not only force you to buy a heavily oversized unit, you’ll also scald yourself or require to mix it with cold water (@20°C), which defeats the purpose of having a lower-temperature gas heater. A lot of studies have been done on comfortable shower temperatures, and most of the studies conducted resulted in about 40-42°C.
Sorry for the long post.
No not long, good post. Appreciated.
You applied a bit more logic and real worldness to it. 🙂
I want to interject though, that the “what you save per month” sometimes does not matter. I think looking at what it costs per month, then seeing how many years/millenia it will take to recover the cost of switching a system, is not going to win, and probably not the point at all.
If I throw a bag of money at a gas system, that will be me considering it a once-off, lump of money that is invested into a new system, gone forever. My “Saving” comes from what I then save every month after that (and after the fact that I considered my lump sum is now gone). So I will actually save R109/m and I will save on the days of loadshedding (not by currency, but by frustration and proper hygiene 🙂 )… and I will save when I need to shower immediately after the wife (no cold geyser).
I think it’s a bit of a no brainer, gas will make sense for someone like me, and will beat electric 5 times over. At the time of this comment, my prepaid meter took 200c/unit to load up 🙁
No one has mentioned using a heat pump what would the outcome be using a 450 watt heat pump
Roy
Very interesting study. Unless I looked wrong however – and in response to your comment that electricity is consistently cheaper than gas throughout the country – If you consider that a basic charges in Joburg City on the Single Phase Domestic Tariff is R442.02 before you have consumed a single unit of electricity than the gas wins hands down. You cannot only use the cost per unit parameter. You must factor in the monthly Service and Network Charges too.
What I need to know, is how efficient is the gas geyser. I want to install it, because of the little size it takes up. But can it be used with the mixers already installed?
I look at the comparisons you have and my question is ;
I had a 100lt Electric geyser and water bill was around R 620-00 now installed a 20lt gas geyser and water bill has risen to R 960-00 can you Please give me and explanation . Will you let me know via my email to show the tenant , is he abusing water as the gas electricity comparison I am still busy with .
Kind Regards ,
Johnny
Goos day to all. It is like Marlyn said, it is a 1 x investment. and therafter you save. If you can afford a solar geyser system, you pay nothing afterwords. You can still use a small gas heater as a back-up system for the rainy days. A 150-200 liter system can cost you anything from R15 000 upwards. In some instances you can use your existing geyser if it complies to the solar system requirements. The sun energy is free.
I have solar panels and a heat pump as backup due to weather . Another problem with solar is after one has showered at night there is no hot water until the sun shines again. It works very well as we only use about 450-500 units per day. We have a big house , three fridges and everything stays on. We live outside George on the coast.
After doing a lot of reading about all the comparisons of cost versus system ,I decided to install a small gas heater system if the electricity price increases by around 20% as predicted and set my heatpump to kick in at a lower temperature. The gas usage will be offset by the increase in electricity and gives me the best backup should there be a power cut and no sunshine. It is more for convenience .
I must state that we first went the route of LED lights and A++ , A+++ fridges , washing machines and dishwashers.
I would advise that route first before paying all the extra money that will take a long time to recoup. At least you have new appliances.
We also received subsidies from Eskom before they cancelled it.
If you can , solar panels first with a normal geyser and then it your personal choice . The cost varies and each has advantages and disadvantages. Leon
Hi Leon, thank you for your input. We are building a house in Knysna and have to consider the options. Did you now install a gas water heater as well as a heat pump on top of the existing solar system ?
Just a correction, it is 450-500 units per month not day .
Ok, now 2 years later the story is a bit different. Gas is cheaper per kg and electricity MUCH more expensive. It is now R723.8 pm for an electricity solution and R467.05 for gas. A R256 pm difference. You add to that the fact that some homes have 2 geysers. Also, an increase of 19% is now again contemplated by NERSA which if granted, will make electric geysers go to R861.32 pm. It is very clear that electricity is much more expensive than gas solutions. Although gas is not the cheapest alternative, electricity will always be more expensive than gas.
Hi Sarie in your plans make provision to harvest rainwater and to sanitize it into potable water with municipal water as back up.
My problem though is that the pump station that feeds my house is on the same electrical grid that feeds my house. This results in that when the electricity fails I do not have water pressure for gas or electricity. I do have a generator as backup which can run my geyser, but fuel is an expensive way to create electricity and I still do not have water pressure regardless. Will have to invest in a water tank and a pump to supply the house and then maybe use a small gas geyser as a backup for emergencies, or maybe make an arrangement where I can use the gas normally and just swap the inlet from municipal to tank water. Do not know whether a small water pump will give the required pressure to shower though, Might just have to run a bath but I am now complicating the plumbing.