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Gas vs Electric Geyser Test

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.

gastestrigs

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.

53 thoughts on “Gas vs Electric Geyser Test

  1. 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.

    1. 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 🙁

  2. 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.

    1. 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?

      1. 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

        1. I have a Gas and a electric geyser, yes an electric is less troublesome but with the gas I save +/- R800. 00 on a family of five. In winter I use more gas cause the settings is higher. I’m using the gas geyser for around 2 years & loving it.

          1. I’m with you on this Rashaad. I think what was not accounted for are things like water and gas flow rate etc. I have a 12L constant temp gas geyser and it is setup to be just right for our use. I use 1 x 48kg about every 4 months obviously being mindful of our consumption. A 20L geyser will burn through gas a LOT faster than a 12L. Do some homework before buying or even just doing a random test. Interesting but as stated irrelevant as I also save a ton of cash with my gas geyser, not to mention the fact that loadshedding does not affect me. Also most electric geysers are 2000W+ nowadays. 55 degrees is quite low for an electric geyser and will not switch on and off frequently if well insulated. Under normal use that will not be the case I suspect. Too many variables in my opinion but that’s exactly what it is….an opinion. FACT is I do save at least half compared to electric in a real world scenario. You can tune a gas geyser to be way more efficient if you don’t need multiple taps open at the same time or water pressure so high it will take skin off. If your idea is to save then consider save the water as well as the gas. Don’t get the biggest because you think bigger must be better. I didn’t even read further but I can only assume other people had similar arguments. Good article though and well documented. Thanks

      2. The test methodology applied here is completely flawed and irrelevant in comparing the costs of heating your water requirements between an electric geyser and a gas geyser. The purpose of a gas geyser (tankless) heating system is to only heat the water you need, and to eliminate the wasted cost of heating and re-heating your 100lt geyser just so you can shower twice a day. It would have been better to compare the true cost of 2 households with the same number of people – 1 household running an electric geyser and the other running a gas geyser. The data on water usage, electricity costs and gas costs for the period of study could then be analysed and compared.

      3. If a person showered 10 minutes in the morning and 8 minutes at night the gas geyser only heats the water 20 minutes
        in total . The electric geyser will have to heat the entire 100 litres in the electric
        Geyser for at least 1 hour in the morning and 1 hour in the evening = 2 hours
        Gas 20 minutes
        Electric 120 minutes.
        Gas geyser is more convenient and as supply of water is instant and it ONLY heats what you use.

        1. Using unit prices in June 2021 provides very different results. Electricity at R2.34 KW/h and LPG gas at R27.00 kg.
          Working back from the experiment above, 385 KW of electricity was used in a month, and 21.12 kg of LPG.
          This changes the costs to around R900 p/m for electricity and R570 for gas.
          Based on municipal and gas dealer costs in Pretoria.

    2. 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.

  3. 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?

  4. 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.

    1. 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.

  5. 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 ?

  6. 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.

  7. 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.

    1. 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.

  8. 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.

    1. 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

    2. Yes I agree also they don’t mention the amount of water that goes to waste when waiting for the hot water from the electric geyser where gas geyser can be right outside and be instantly got.

  9. Ama`s response(2nd): the geyser operates UNDER NORMAL CONDITIONS WITHOUT A TIMER–see test conditions, thus making this test RELEVANT.

  10. 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.

    1. 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 🙁

    2. Hennie, you cannot do a comparison with the water heated to different temperatures. This makes no sense. The water coming out of the hot water tap needs to be the same in both cases for the comparison to work.

  11. 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.

  12. 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?

  13. 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

  14. 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.

  15. 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

    1. 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 ?

      1. My electricity works out R3.83 per kWh. There is no way it can be cheaper than gas at R125 (pensioner) for 9kg.

        Further Eskom increases by 14% in 2019…

  16. 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.

  17. Hi Sarie in your plans make provision to harvest rainwater and to sanitize it into potable water with municipal water as back up.

  18. 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.

  19. All good and well…
    but since I replaced my geyser and stove wit gas ones, my bill drop with +/- R600-00 per month…
    Do you work for ESKOM..?

  20. I replaced my electric geyser with an instant heat gas warmer. I also put in a 6 burner gas stove, My electricity has dropped by R 1 000.00 a month, I use 1 x 19kg gas per month R 460.00. This has been over a 3 month period April to June. This will increase now that electricity tarrifs are being increased. Non scientific, normal usage. Had to educate the family to only use hot tap when need hot water as kids use any tap for anything.
    Definitely a plus with power cuts.
    Purely my experience of gas vs electricity.

  21. When this experiment was contacted in 2012 electricity price per unit was R1.22 vs R2.29 it cost today i.e. an increase of 87.7% in electricity cost; whilst the cost per kg of gas is still about R23.33 per Kg (slightly cheaper than when the experiment was conducted).

    So using the units of electricity vs gas as per the experiment, to heat the water in 2012, gas was +/- 7% more expensive than electricity. Now, however with the sharp increase in electricity prices (since then) the 336.3 units of electricity would cost R770.12 vs the R464.50 cost of 19.91kg at today’s price. Therefore heating water using gas is now 40% cheaper than electricity, again using the units of gas and electricity used in the experiment.

  22. Electric geyser bill is 1200 in summer,( winter bill you go sick),replaced with gas geyser and bill hasn’t gone over R500 currently at R477
    7 kg gas last 3 months for a single bath for two people. Saving R723. A single month’s savings covers gas bill for 12 months, so remainder 11 months recouped my investment twice over. Important thing is the size of gas geyser, 5lpm is more than sufficient to me anything larger is overkill. Factor in water savings gas wins hands down

  23. I need more information what is involved in converting from electricity geyser to gas heating please. Any help in the sense of your experience in planning and having it installed would be appreciated.

  24. Hi All, I am thinking of selling gas water heaters since lockdown has cost my regular job. I have a lot to understand but the opportunity may not be available forever.
    Please advise me on how to proceed and if I would /would not be wasting my time and resources on this venture.

    Thank you kindly for your responses

  25. Thank you for the test however you are saying that all the gas was used for the test.
    A 5min shower uses approx 50-100l of water depending on the shower rose but a 48kg or in this case a 45kg bottle of gas will last longer than a month, particularly in summer. If not all the gas was used then the cost of gas usage is not accurate.

    1. They didn’t say 45kg was uses but only that a 45kg cylinder was used. 19.75kg was used if you look at the test results.

  26. Weighing up our options to replace our burst electric geyser now too. Quick question about loadshedding: do you need electricity to ignite the flame for a modern gas geyser?

  27. You also missing the fact that when you go away for the weekend / Holidays the gas is not used at all
    The electric inevitably is always left on even though we always say we will turn the geyser off when away.
    So the Electric geyser is just wasting away……

  28. Can we request this test to be redone. Leaving an electric geyser on vs heating up all the cold water from minus XX is a balancing act. Where we live its to cold to switch it off.

    Municipal eskom rates is now much higher, R2.00

    Hope to hear from the you soon

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