The Gas Company. Gas Lifestyle Merchants. Gas | Installations | Appliances

Gas Geyser Introduction

Let's first agree on some semantics.

The poms call thisa geyser.

The yanks call thisa geyser.

When we are talking about gas geysers in South Africa we are almost always talking aboutinstantaneousgaswater heatingsystems.

You do also get gas water storage heating solutions, but they suffer from the same efficiency shortcomings that the old donkey currently in your ceiling suffers from. So you'll be hard pressed to find them.


The ″instantaneous″ aspect is really significant. You know how those dodgy marketing shysters Pritt evocative words to crappy objects to make you fall in love with 'em? We'll instantaneous in this context is friggin nothing like that. These things really are instantaneous, they heat the water as it flows through. The water enters the unit as cold as a witches heart and pops out the other side as hot as twin-6'-Norwegian-Cosmo-models juggling chainsaws. The big units generate around 50Kw of energy, which is about the same power output as the Honda we bought granny as arun-overrun-around last year.

We make a really big deal of this instantaneous thing because it gifts us two things of epic beauty.

  • We use zero energy unless we are actually consuming hot water
  • We can never run out of hot water

The first point kinda speaks for itself. All the non-instantaneous (so storage) units available (including your crappy electrical unit you currently have) keep warming the water in the storage tank all the time. This is so that when your grace decides now you want to wash your ass, the hot water is immediately available. Instantaneous units change up this design, when you need a scrub, you open the tap and 50Kw of thermal energy beat the water into being as warm as you want it to be. Turn off the tap and there is peace in waterland again. There is no need keep the water warm because ″instantaneous″.

"Never run out of hot water" is perhaps a bit cavalier, you can run out of hot water. If you run out of water or if you run out of gas. Get a borehole if the first point scares you. And if you ever run out of gas I really can't respect you anymore, you can only blame yourself! Also, get yourself hooked up with🖧 telemetryand this will never happen.

A word about Ignition.

In order to achieve combustion you need 3 things. A combustible material (gas), oxygen and a spark to start the process. So your geyser is gonna need a way to generate a spark, and there are 3 distinct solutions on the market to achieve this.

  1. Electrically powered ignition
  2. Hydro powered ignition
  3. Battery powered ignition

All the higher output geysers use electricity to achieve this high output (among other things) and obviously once the unit is using electrical power anyway, you may as well generate the spark using this power source. So all the high output units use electricity for spark generation. If you pick a unit that requires electrical power, it'll use electricity for spark generation.

Hydro generation is genius. It works by using the flow of the water through the geysers when it's on to turn a tiny little turbine which generates enough power to cause a spark. The benefit is that you will never have to replace batteries. At the moment only one range is available on the market with hydro ignition and that's the Bosch mechanical range.

All other units are battery operated. Battery operated ignition is a very simple solution for mechanical units that have no electrical power supply. Batteries need to be replaced every 9 months or so, and apart from batteries running out the ignition system runs flawlessly.

Water Flow Rate (~Pressure).

Trying to understand the relationship/difference between water flow and water pressure is going to do your head in. That's why we end up using the two terms interchangeably. Flow rate is actuallyperinversely proportionate to the pressure (think about it, when you open the tap you increase the flow rate from 0 to some few litres per minute, and drop the pressure). Flow rate is measured in litres per minute, pressure is measured in Bar or Pascal.

Pretty inconveniently, geysers are rated in litres per minute (at Δ 25 ℃.), and water piping systems are rated in bar, and there is no way to directly convert between the two. Things like thickness of piping, type of piping, number of bends, run length of piping all affect the pressure to flow rate ratio.

Water pressure, and therefore water flow affects two things:

  • Quality of the shower experience
  • Geyser ignition

Municipal water supply in the 'burbs is usually somewhere between 2 and 6 bar, but can be lower or higher depending on you pipe sizing, distance from water tower, elevation relative to water tower etc.

Anything below 2.5 bar and you're approaching pretty kak welfare-shower territory. Pressures of around 6 bar and you may want to regulate the pressure down before you wash your skin off.

Instantaneous gas water heaters have an operating range for input water pressure and it differs from model to model. What's salient here is; if your water pressure is anything above 7 bar or anything below 1.5 bar you gonna need to remove some of the models from your consideration list cos they won't work.

Thoughts on Piping

Like cream, and playboy bunnies, thicker is better when it comes to both water and gas piping. You can never go too thick, but you can certainly find your piping is too thin to supply the geyser effectively.

There are a few things that'll effect the piping thickness requirements:

  • Length of pipe
  • Number of bends
  • Thickness of pipes
  • Number of geysers
  • Series vs Parallel
  • Size of geyser(s)

As a rule of thumb, for gas reticulation, units below 20Lpm can get away with piping smaller than 20mm in diameter, units 20Lpm and larger require piping thicker than 20mm.

Be Uninterrupted.

You can be independent or you can rely on the State. If you choose to rely on the State then you cannot live uninterrupted. End of discussion.

Policing, health care, education, electricity supply, these are all areas where the State has a proven track record of sub-optimal delivery. There is no coherent reason to believe it will change.

Take a very simple ″policy decision″ of your own and reduce your reliance on the State and you get back in control of your lifestyle.

The thought of running out of gas in the middle of a shower with a head full of shampoo-lather and a dripping saggy bottom causing you anxiety?

Gas-on-tap means never running out of gas and never having to collect your own gas and no massive monthly bills when that bad boy does eventually run dry

tell me more