How Does A Gas Geyser Work

Here we will go over how a gas geyser works. We will cover all the details, types of geysers and if you should use one.

What is a gas geyser

How do gas geysers work

Types of gas geysers

Should you use one


A gas geyser is a water heating system that runs of gas. The traditional south African gas geyser does not have a reservoir to store hot water, instead, it heats the water instantly. The gas geyser will be only activate when there is a demand. For example if someone opens up the hot tap the gas geyser will activate and send hot water to the tap. When the tap is closed the gas geyser will deactivate and stop producing hot water.

How do gas geysers work


Here we will go into greater detail of how exactly a gas geyser works through the steps of a gas water heater’s operation (assuming the gas and plumbing installation is complete).

Step 1. Demand

The hot tap is opened. Once the hot tap is opened the gas geyser will detect that there is water flowing through the gas geyser. The water flow is detected via a dynamo (electronically) or through a diaphragm (mechanically).

Step 2. Ignition

Once the Gas water heater detects water flow it will try to ignite the gas. The gas geyser will allow a small amount of gas to flow into the combustion chamber. It will ignite the small amount of gas with a continuous pulsating electric spark. Then the small amount of gas is lit and the pulsating electric spark will continue, however, it becomes inaudible. The reason the spark continues sparking is because the gas geyser will detect that there is ignition through flame rectification. This is when an electrical alternating current passes through the flame and is picked up on the burner. More on flame rectification here


Step 3. Combustion

Now the gas geyser knows there is ignition, it will allow gas to flow to the rest of the burners. At this point the fan will activate to assist combustion if it is a force driven gas geyser. The gas will ignite on the rest of the burners and the heat that is produced will pass through the heat exchanger.


Step 4. Heating

Now finally the water passing through the heat exchanger will get heated by the hot combustion gasses and this heated water will ultimately reach your tap to enjoy.

More on Heat transfer here:


Step 5. Demand Ceases

When you are finished using the hot water you will close the tap. Once that happens the gas geyser will detect that there is no more flow and it will deactivate the gas geyser.

Types of gas geysers

Natural Draft:

Natural Draft gas geysers make use of the natural principle of hot air rising. The hot gasses produced from combustion rise up through the heat exchanger and then, in most cases, through a chimney, which normally assists in the draft.

How chimneys work:

Why Hot air rises:

Fan Force Driven:

Fan Force Driven gas geysers make use of a fan to assist in the complete combustion of of the gasses and then to force the combustion gasses through the heat exchanger. Fan Force Driven gas geysers are generally more efficient than Natural Draft and can supply a lot more hot water per minute.

Should you use one

Yes. For the simple reason that gas geysers supply endless hot water (granted there is gas). This makes gas superior to solar or electric alternatives. With that being said, there are definitely merits to using solar but you can have the best of both worlds.


Most (if not all) force driven gas geysers will allow you to feed hot water into the gas geyser as long as the incoming temperature does not exceed the manufacturer’s specifications. Solar installations should include Tempering Valve which will ensure that the solar water heaters output does not exceed the set temperature.

More on Tempering Valves here:


When you feed the heated water from the solar geyser into a supported gas geyser it will detect the incoming temperature and will only activate the gas geyser if necessary. And if the water needs to be heated the gas geyser will only consume a small amount of gas to reach the target temperature.


For example: if the incoming water temperature to the gas geyser is 39 degrees (from the solar geyser) and the gas geyser has been set to a temperature of 42 degrees the gas geyser only needs to increase the water temperature by 3 degrees.


Whereas normally the incoming temperature is 16 -20 degrees (groundwater temperature), which means the gas geyser will have to heat up the water by 26 – 22 degrees. Which will consume more gas.


So it makes sense to buy a Fan force gas geyser first and perhaps over time add on a solar geyser. That way you drastically reduce the amount of gas you consume but more importantly you will not run out of hot water.