Heating water: Options and Insights please

Good day all.

I’m hoping to lean on the goodwill and mass of insight amassed here. I’m also hoping on taking a shortcut by asking directly, not for an answer nor exact solution, but at least what direction to focus on for though I’m no cretin I am not technically minded by nature and do not have hundreds of hours to read page after page of marketing. I find all the information dizzying and every “boykie” I know knows everything except those solutions he didn’t pay for.

The situation currently:
150L 3kw geyser. 9yrs old.

The house is a bit odd, but let’s say the geyser is in the ceiling space above the bathroom, about 5m from the kitchen. The IBR roof above the geyser faces 140deg. (ie SSE) at a 30deg. pitch. There is nothing on this roof except dust. The geyser is easy to reach and sits below the outside eaves/gutters.

My solar system is small, 1200VA multi / 1x US2000C Pylontech / 4x JA 385W (2S 2P) / 150:35 MPPT / Cerbo etc etc.

So for the purposes of ‘which direction to explore’:
I’m based in Pretoria East.
The roof mentioned gets good sun in summer and ok sun in winter.
There’s enough wall space outside to mount a heat pump.
Not a massive budget.
Can do installation mostly myself, despite not being too technical I am handy.

What do I hope to achieve
At best no longer heating my geyser from the monkeypality.

As far as I can tell the solutions potentially best suited to me are either ‘Evacuated Tube’ or ‘Retrofit (pumped solar geyser system)’, well there’s the Thermosiphon option too. Thing is it seems whether one goes for a retrofit that requires pumps etc or a new Evac-tube jobby the price looks about similar. I’m also wondering whether one could have a new Thermosiphon that then also feeds the old geyser, thus ending up with almost 300L of water…though what’s the point, right? Now I’m splurging.

I hope this is enough information for folks to comment on. Any questions I’ve left out please ask.
Thank you.

If I may …
Had EV tubes in CPT, man, they WORK!
My Brother did flat panels in Jhb, he loved it.
Looked at heat pumps a while ago, or adding more solar panels, grid-tied.
Looked at Solis grid-tied dedicated to feeding the “house”/geyser.

Had a 2kw element to “fit” the inverter, and put it back to 3kw when the geyser was replaced. Cents on the rand I figured, to heat faster.

In the end, I got gatvol, tired of SWAMBO this, SWAMBO that … everything costs a lot of money, and needs to be replaced eventually as nothing lasts.

If I have half a chance, I would go gas for geysers for one reason … heat what you need.
… and it is weather/Eskom proof.
… just have 2 spare bottles at all times.

Till I get that gatvol enough to go gas … people must just switch on the geyser when they need it.
Vertical mounted works excellent for that quick heat and shower. Still the most cost-effective option for me.
Kitchen, 50l dedicated geyser just for the kitchen, always on.
All geysers are B+ rated, they keep temp quite well, even if outside the house.

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unless it is a principle thing, I would first check my actual geyser heating related costs (an energy meter of some kind) and see if if it is as high as you suspect. Then compare costs/priority for focussing on the geyser vs rather saving up for a bigger PV system that might give more overall benefit?


This is not a lot of vooma! I have the exact same PV power dedicated to heat my geyser.
Trying to heat the geyser with PV power needs plenty panels. Better to install EV tubes or flat panel (preferably no heat exchanger but this depends on where you are located)

Hi I have copied a data sheet with different solutions and cost savings. Ranging from geyser, to solar geyser, heat pump, heat accumulators(most efficient by a mile) and gas( R for R fairly one of the most expensive. Zinniadraughting@gmail.com, email me and I will forward you the info and some advise. In general there is a lot more you must consider before deciding on a system. Like amount of people using the system, and very very important is the time of use. It is also important to actually take your bathroom setup into account, eg. Is there a big flat bath, or 2, how often do you use it, showers, how long do you stay in the shower on average. The other factors comes down more to the universal facts like, sun intensity, orientation, latitude etc. As example, solar geysers works great in Limpopo province, but in the garden route they suck


If you want to comply to SANS 10400 XA, then you need to subsitude 50% of your hot water generation by other means than electrical heating. Increasing your Solar PV to cover those costs means you are going to be generating your power thru the sun during the day, that sounds fair, but it’s still electrical heating, if you remain with the normal geysers, which means that you are not complying to the rule. A 150 L geyser has a 3 kW element installed. Direct heating thus, when it switches on for 1 hour u use 3 units, as 1unit = 1 kW/h. This means that should you choose to still cover conventional geyser loads thru solar, you would need to increase inverter capacity by min 3 kW and install 6 panels. Which outweighs the cost of a new solar geyser or Heat accumulator. Gas would be cheapest to install but probs most expensive to maintain. The other thing to keep in mind is that the solar option still won’t heat up the geyser at night or during loadshedding, unless if you increase battery size aswell. Now having 1 3 kW geyser running a whole family means that this geyser would be running minimum 3 to 4 hours a day, and if time of use is not favourible, like when the wife needs to bath at 20h00 in the evening, she will probably drain that sucker and it will put extra pressure on a battery system. Thus to cover a 3kW geyser thru battery you need to look at adding 10kW battery pack to stand a chance…if geyser usage is reasonable.


I can confirm that. Heating water with gas is nice, convenient, load-shedding proof, but it’s not much cheaper. It certainly didn’t feel cheaper, and on paper it was only marginally cheaper (due to eliminating the standing loss). Having to remember to order gas (because 48kg bottles are hard to transport if you don’t have the right vehicle), and the occasional shortage on LPG in the area, certainly made it somewhat inconvenient at times too.

Of course I moved into a house that already had a gas geyser, and an electrical one for backup. Because I didn’t install the gas geyser, I didn’t suffer from the confirmation bias that many get after spending a heap of money on it. At one point, during the pandemic, we ran out of gas and switched to electric for a few weeks. The cost difference is marginal at best.

What happened here:

  1. There is a law … “thou shall not bath”.
  2. You shall shower like #DayZero
  3. Geyser heats once per day during optimal sun hours when other loads are less, spare solar … fit into the time slot.
  4. Shower at similar times … all in the mornings or all in the evenings.

Now that may sound strict with some wanting to shower in the mornings, others in the evenings … if you have a family then like with everything in life, there are compromises to be made … or pay substantially more.

Adding to your salient posts:
Sometimes people just need to be given fewer options … can turn out to be the best cost-saving ever, and they don’t mind at all, never knew they would not care.

Also learned that a vertical geyser, the temp sensor on top of the outlet, can save a ton of money in heating costs for quick showers. Just heat what you need. If not using solar. When using solar, heat the thing as hot as you can.

And B+ rated geysers, they are now standard I think, does keep temp for 24h easily.

If not building new or doing alteration does SANS 10400 XA apply retrospectively in terms of means of water heating? If not, how is it relevant?

OP indicated 2-person household.

OP also indicated the motivation for investigating water heating options is to reduce monthly costs and having a limited budget to put towards this. Without knowing the OP’s actual hot water and general electricity use, the number of hours that his/her geyser will be heating water etc. will remain speculation. Therefore, I suggested to determine whether that is in reality of his/her situation a meaningful place to focus - If it is, then all the various options become relevant. They might find though that leaving the geyser on the grid and having the capacity to shift other loads to PV/battery saves more - if so, that might be an avenue to explore.

I have no horse in the race.

If you need to submit plan for approval that include anything with the hot water (bathrooms, kitchen, sink) then SANS 10400 XA apply. If you just add a bedroom or afdak you can keep your old geyser system as it is.

As I recall though, the existing system has to be adequate for the proposed extension. I remember my architect asking about that: Oh, 200 liter tank? Yeah, that is adequate, no need to tamper with that.

Thank you, I shall.

I should have added that I also want to buffer against increased chances of not having power at all. Here in Pta.East we were having black outs lasting weeks a few years ago. The sub-power-station servicing us was constantly breaking down. So we’ve been spared all loadshedding since April '22, basically the month I put in my small solar system. But recently, barring the cable theft we’ve been experiencing the beginnings of 2-3day black outs…just once so far, but that’s enough to put the heeby-jeebies back into me.

I take your point, thank you…will work on it.

Hi, it is relevant - if you apply the law correctly (which very little people do).
Example: a house with an existing solar geyser (150L) and a normal electrical element heated geyser.
In this case - should the electrical geyser burst - you may exchange it for another electric element heated geyser, because SANS 10400 XA says that 50% of all hotwater heating must be achieved thru other means than electrical element heating.
Example 2: a house with 1 existing normal electric element heated geyser burst:
In this case you are not allowed to replace this geyser with a normal electric element heated geyser, and should instead install a solar or alternative heating system - to comply to current regulations.
you cannot continue to apply replaced and disgarded regulations when you need to change a geyser, you have to apply the current law, and first see if you comply to this rule. This is strictly by the book off course, and not many Plumbers or electricians know about this. The same with most municipalities - but you have to ask yourself what is the purpose of the exercise, including the purpose of the regulation. It was developed firstly to reduce our carbon footprint, which means automatically a reduction in demand on the grid - which will lead to less coal burned unnecessarily, and less pollution in our skies.

Yes it will remain speculation - it should be measured to get an accurate reading - leaving it off the solar is the best option if budget is a problem, but, whenever that geyser need to be replaced, it should be replaced with a more energy saving option - like the heat accumulators, or heatpumps. Solar geysers are hardly used in the rest of the modern world anymore - because of all the associated problems with it. It is not the standard. We inherited solar geysers because our standards are old (even SANS 10400 XA was implemented in 2010, but its data and format was taken from international standards written in the 80s). We are playing catchup with the rest of the world and have become the old dumping ground for in affective systems

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So… is the insurance company going to pay for the more expensive replacement? That’s what I am curious about :slight_smile:

…before I look at a energy meter let me say:

We take four plus-minus 8min showers per day, wash dishes once or twice/day about 20L of hot water a pop. Geyser set to 60Deg.

good question - but im sure if they are made aware of the law - they will have to.

any idea of your flow rate/min? as example - if your flow rate is 10L/min - it means you are using 4 x 8= 32 min of water for showers @ 10L/min = 32 x 10 = 320L . On the showers though we can assume that 70% of volume is hotwater and 30% is cold water mixed into the system, thus (320L x 0.7) only 224L of hotwater are used through geyser for showers.
40L on washing dishes (sounds like alot of hotwater for dishes though)
Total hotwater water used is thus +/- 224L + 40L = 264L of hotwater used.
Now taking into account most of this would be split between morning and evening, I assume, it means that you are draining your geyser twice per day rather continuedly by 132L at a time.
This means your geyser will be cold as hell as cold water enters the system to get heated and it means your element would be on at least 2&half hours in the morning and the same in the evening - thus
if geyser has 3 kW element - it will be using 7.5 units to heat twice per day in this scenario.
NOTE::: this is an example on how you can work it out and based on an estimated flowrate of 10L/min.
If your flow rate is 6L/min, the calculation would probs work out 40% less than what I got to.

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I’ll check. Thanks for the calculation example.
I reckon my estimations were very generous, especially with the dishes. more like 20-25L/day

Besides it’s bad for the resale value of the house!