How To Install A Gas Geyser

Here we will cover the basics of how a gas geyser is installed.

Where To Position a Gas geyser

Water Piping

Gas Piping

Note: the gas line for a gas geyser must be installed by a registered gas installer.

Position of gas geyser

First the gas geyser is mounted on to a wall. The position of the gas geyser is very important. Besides being installed according to SANS, it is important to install the gas geyser as close to where hot water will be used. The reason for this is:

  • The hot water takes time to get to your tap. Gas geysers will heat up water virtually instantly, however, the water that is already in the pipes needs to “move” out of the way before the hot water can get to your tap. So the shorter the distance the hot water has to travel to your tap the shorter you will have to wait for hot water.
  • The longer the hot water takes to get to your tap the more heat it will lose while travelling to your tap. This happens because the heat will transfer from the hot water through pipes to the colder air. This heat transfer can be reduced by Lagging your pipes. So the longer your pipe run the more heat will be lost.

Water Piping

Pipe sizing

Now, what I’m about to say some plumbers may not agree on but it’s worth mentioning.

The general idea in today’s day and age is that bigger is better, for the most part, that is true, but when it comes to the size of your hot water pipes the shorter and thinner the better. Here’s my reasoning.

The wider your pipe the more water you will waste when you are waiting for the hot water to get to your tap. This is simple math V = π r^2 h. The wider the pipe is the more water it will contain and therefore the more water you will have to move out of the way until your hot water reaches your tap.

Here is a table on how much water you waste each time you open your tap to wait for warm water.

Pipe size

Pipe Length

Amount of water wasted



1.06 Liters



2.28 Liters


As you can see using a 22mm diameter pipe will waste just over twice as much water each time you wait for hot water. That adds up over the course of months and you are paying extra for very little benefit. Most water supplies do not supply enough flow and pressure to saturate even a 15mm pipe so going beyond that size doesn’t make much sense.


Before you go out and buy only 15mm pipe you should examine your water flow and pressure. If your supply of water is greater than 18 litres per minute you should use 22mm pipe. If you go smaller than that you are at risk of having noisy water pipes so choose wisely and maybe consult an experienced plumber.


So now you know where to position your gas geyser and what size water pipe to use but what about where to connect the hot water pipe in the roof.


First, you do not have to get rid of your existing electrical geyser, simply install an isolation valve at the outlet of the geyser and connect the hot water coming from the gas geyser anywhere after the isolation valve and turn off the power to the geyser. I might also be wise to add an isolation valve to the inlet of the geyser and then drain the geyser completely, just make sure that the geyser is not on (electrically).


Most people would run the hot water line from the gas geyser to the output of the existing geyser, just after the isolation valve as shown here.

This will most definitely work. However, it might make sense to T in as close to the nearest, most used tap. For example, if you will use the shower the most then you can T into the hot water line as close to the shower as possible.

This minimises the length of pipe necessary which is good for reasons as we have discussed above and might make your installation a bit cheaper.

Gas line

We have already stated that only a registered gas installer should install your gas geyser. Here are some reasons why this is important:

  • Manufacturers will not honour their warranties if the unit was not installed by a registered gas installer.
  • Doing it yourself is illegal and could be dangerous.
  • You can damage your gas appliance if you install it incorrectly.

So what follows regarding gas is just for gas installers or for your reference.

Length of gas line

The length of your gas line is very closely tied into the size of the pipe. But here are some considerations:

  • The distance from a force driven unit to the gas bottles should be more than 5m. Simply because force driven units require an electrical source (not more than 80w) to drive then fan for complete combustion and the gas bottles need to be 5m away from any source of ignition.
  • The distance from the gas bottles to the gas geyser should be kept as short as possible, so 5m and no more if possible for force driven gas geysers. And 1m and no more for natural draft gas geysers. If however, you need to go longer you need to follow best practice in pipe sizing in relation to the demand of the gas geyser and the length of the pipe, more on this in pipe sizing.
  • The longer your pipe run the more expensive it will be. If you are too expensive you won’t get the job and may turn the customer off of gas in general.

Pipe sizing

If the size of your pipe is not wide enough you may starve the gas geyser of gas and it will not perform optimally so its best to size your piping accordingly. There is one alternative when you need to do a long pipe run and don’t want to or can increase the size of your piping. That is using two regulators, one high-pressure regulator at the bottles and one-second stage (2.8kpa) regulator at the appliance.

Gas pressure

One very important thing that needs to be checked is gas pressure at the gas geyser. The gas pressure should not exceed the rated pressure as labelled on the unit but (in the case of having a long pipe run) too little pressure is also not good. So adjust your regulators appropriately.

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