By Patrick Gordon – consultant
These are very handy units especially for installations that require hot water but are far from a Hot Water Cylinder (HWC). These small HWCs are easy to install and can be installed where only a cold-water supply and electricity are available. Even though some of these units have a high-pressure rating, they may not legally be installed in South Africa as a pressurised system.
This may sound confusing but it is easily done using a specially designed mixer that can be sourced from your plumbing merchants
What makes this mixer different? The mixer may look like a normal mixer when it is installed, however there is one subtle difference. You can identify the mixer by three flexible connection hoses instead of the usual two.
The fist pipe is connected to the cold-water supply (this can be connected directly to the cold-water supply in the building). The next pipe is connected to the cold-water inlet of the heater, and the third pipe is connected to the hot-water outlet on the heater.
The way that the mixer works is if the hot-water side of the mixer is opened it takes cold water from the supply and pushes it into the heater. When this happens the increase of pressure is immediately discharged via the third pipe to the outlet/spout of the mixer and no pressure is built up within the terminal installation.
Any expansion that occurs during the heating process is also immediately discharged via the mixer outlet. Due to the expansion that is going to take place the outlet of the mixer will drip water. This is not an indication that the mixer is faulty, but simply the system discharging any pressure buildup during the expansion taking place while the cold water is heating.
Typical open vent mixing control valve unit for under-sink water heater. Drawing by Tanya Olckers
To make the installation legal, this is the only way that it may be done. Remember that all SANS 1025 regulations apply to this type of installation with special instructions in point 4.1.3.e.
Make sure to make note of any of these units that are incorrectly installed (there are many out there) when you issue your non- compliance notice.
For any further information on this topic please contact the writer: PA Gordon on patrickg@splashworks.co.za.
Register for free to gain access the digital library for Plumbing Africa publications
