Running Geyserwise in conjunction with a gas geyser

Hey all.

As the title says, is this a possible config?

At the moment I have a Geyserwise system and with Eishkom’s pending increases, thought it wise to investigate doing a gas geyser install as well. We are 2 adults showering and 2 kids who for now are young enough to share a bath (FTW).

In my head it’s as simple as having the Geyserwise water flow from the outlet to the gas geyser. It then decides whether to warm it or not. And then sends the water back to continue its path in the outlet flow.

Had a gas guy out and he spoke me in circles and I’m more confused than ever now.

I hope that makes a bit of sense. Thanks all.


Which Geyserwise system do you have?
And is this a question for overcast days?

Yup for winter basically. On the overcast days it warms to around 30 degrees. Looking to bridge the gap on those days. Whereas on rainy days, we have to turn the electricity on for longer. Thought instead of going with electricity we would use gas instead.

Checked the roof, it has 2 solar panels. I see some pipes as well. Then in the roof, there’s a Geyser as well. Not sure how to check the type? Attached a picture of the console though.

What size geyser do you have?
It’s only for the 100l geysers that they recommend only 2 panels.
I suggest you start off by a adding a panel (or 2)

Hello there, I have two PV systems, but a bit nervous to post the link so let me post the picture

This is a typical 150L geyserwise , a 200L will have four panels. There was a chat this week about this. I would have the Gas heat the water into the Geyser, I see you are looking at the other way. Look for the chat on the forum on the thoughts of this Gas > Geyserwise system

I would top up the heat after the geyser using gas… that way you guarantee a certain temperature year round. Less gas in summer and then more in winter. Some names have been mentioned (Bosch was one, Rennai or Paloma).

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How about if you had a geyserwise and it already had the temp at say 55c by 18H00, when someone does this 20H00 8pm bath / shower to 21c, the gas replenishes the hot water leaving on the cold inline with hot water. The new Gas inline can be set to work only certain hours I saw, certain flow, certain heat. Currently the cold water replaces the hot and then we have to run the geyser on AC to bring the temp back to a living temp as the sun has left the room until the morning. Thats my thinking but I appreciate some input of opinion thats different. Another thought. on this. then the cylinder stores the hot water for use at any connection point to that geyser, taps, bath , shower …

Try to get the maximum performance from your existing system before adding another system.
So with your Geyserwise Dual get it performing as best you can.
Hot water is stored energy (like a battery). So heat your geyser up to 90 deg if you can. See @Vassen comment on the other Geyserwise thread at 8pm.
Once you have improved it as much as possible and you need more then look at other options.
Also heating water with gas is no cheaper than with electricity.

Although this can work I think it’s less efficient. If the gas geyser can anyway heat the water as and when you need it, why would you want to heat the water and then store it in the geyser, letting it lose some heat by the morning when it’s going to be used.

Rather let the cold water sit in the geyser and heat it up with gas on the way to the tap. That way you don’t worry about timers or different season, etc.

As @Richard_Mackay and @plonkster have mentioned, gas water heating isn’t cheaper. It’s just a lot more convenient especially when you have cold water in the geyser and a double whammy load shedding early morning.

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I did not know you could do this? Who do I speak to? Geyserwise? And what would a panel or 2 cost? Thanks.

I will have a search, the reason I would do it the other way is because it seems logical.

At the moment we do not use the Geyserwise timers, we simply switch it on and off as desired. In summer it’s basically off most of the time. As we moving to winter the water is lukewarm. Thus in my mind heating the water on demand makes sense. As we are not using large amounts of it.

Thanks for the diagram. And alternative option. :+1:t5:

That would be fine if I required a full geyser, but at the moment I don’t think we do. Looking to do on demand heating of lukewarm water coming through outlet.

The idea was to have it only turn on the gas heating if the heat is say less than 45 degrees. Was hoping that the gas geyser would be able to detect that.

It did not know that. Will have to re-evaluate. Even with the massive 13% increase coming?


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The more expensive gas heaters do this… they just add heat when temp is below a certain setting.

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It depends on a lot of factors. If you have natural gas supplied to your house by pipeline, I suspect the gas will be cheaper. If you have to buy LPG in a bottle, then it is affected by 1) the cost of LPG in your area, 2) the cost of electricity in your area.

In Cape Town, there is the slight odd possibility that gas might beat electricity. You see LPG costs R225 for a 9kg refill, which works out around R2/kWh (if you convert from the calorific content to equivalent watt-hours), while the top end electricity price is R3.30/kWh. So at face value the gas is almost a third cheaper… but then the gas geyser is so much less efficient.

A gas geyser is between 50% and 70% efficient depending on how much money you spend on it. That means the heating cost with LPG is really between R2.85 and R4 per kWh. If you are bang in the middle – which is roughly what my little cheapo Bosch seems to be capable of – the cost of electricity and the cost of gas is the same: around R3.30 for a kWh of heating.

So, in the short term, the 13% increase should favour gas. But from experience I’ve learned that the oil price (and gas by extension) tends to follow, possibly because of supply- and demand in the market. So such advantages are fleeting.

Again I have to come back to one item: The standing loss. And here I may well change my position tonight, that gas may indeed by SLIGHTLY cheaper in Cape Town right now. If the cost for gas and electricity works out the same (as calculated above), but you save on the 2kWh standing loss of a geyser… then technically you’re saving R6.60 a day (approximately) on gas.

That is however still a FAR cry from what you save with a solar water heater (over the whole year of course), or using a heat pump.

Edit: Also note above that the R3.30 I used is the rate for the higher >600kWh bracket. Below 600kWh the tariff is R2.40/kWh. So again it depends on your overall electricity use. If you fit below 600kWh… then gas is more expensive than electricity. And many of us use our solar plants precisely to get below 600kWh…


The Dept of Energy controls the price of LPG.
There has recently been an increase but I reckon they will keep electricity and gas prices in the same ratio as before.
Only private enterprise will drive prices down. :frowning:
LPG-Regulations.pdf (136.3 KB)


Correct. And while I have no evidence for this claim, it does seem that they keep it on par with the cost of other energy sources. If they don’t, well we will soon have LPG shortages, that I can assure you. We already have shortages sometimes… :slight_smile:

I don’t expect that in the long run LPG will ever be much cheaper than electricity. If you really want to save money, you want to look at solar water heating or a heat pump.


Definitely Gas Geyser after Solar / Electric Geyser. External valve can also control the bypass of already heated water.