Frequently Asked Questions

REPLACING A UNIT
In the past, most households' hot water requirements were pretty much standard. The basic needs of a family of four did not change much from house to house. Nowadays, however, with many houses having two (or more) bathrooms, spas and dishwashers, demand can vary between households and in the same household over time. Before just simply replacing a unit, Dux recommends that plumbers ask householders a few questions about their needs to make sure that what they are installing will meet the customers' present and future requirements. If, after discussing their requirements, the owners want the same system they have had, the important point is to replace the old system with a new one on a megajoule-for-megajoule for gas units or the same element wattage for electric units basis. Often an old system has no model number. Sizes and shapes of heater unit change between manufacturers and over time, so comparing the unit's physical size is not a reliable indicator of capacity. To avoid confusion, simply exchange megajoule for megajoule, e.g. 35MJ for 35MJ.

SAFE TRAYS
There seems to be a bit of confusion surrounding the use of safe trays. The National Plumbing Code AS 3500.4 requires safe trays to be installed to all water heaters where, if there is a leak, property may be damaged. Installation of such trays must comply with Clause 4.4 and Subclauses 1 to 5 of the Code. Manufacturers often get claims where the heater has leaked and caused quite a bit of damage to the house. However, the manufacturer's warranty on the heater does not cover damage to property caused by failure to fit a safe tray.

LAGGING
To lag, or not to lag, that is the question. Conventional wisdom has been that everything should be lagged, but this is not necessarily so. You need to lag, if the pipe is in the ground, or in a very large house with long runs, or the set-up incorporates a flow-and-return system. Some experts recommend lagging the first 1-2m of a hot water pipe. However, if the system is close to the points of use then you are not going to need lagging because there is not a lot of heat to save. Of course, on the other hand, if the area is subject to freezing, lagging is essential.

FLOW-AND-RETURN SYSTEMS
As people put more money into their houses, they often expect more of their hot water systems, demanding instant hot water at every outlet. In such situations, the plumber should be looking to install a flow-and-return system. Dux recommends that plumbers have a flow leg (A-B) and a return leg (B-C), if possible. All the taps and fixtures should come off that flow leg while the return leg will be a reduced pipe size and start from the last fixture back to the unit from B-C. This system constantly circulates hot water around the house to every outlet. Such a system can be running all the time or it can be on a time clock. It is essential that all piping is well insulated with a minimum of 15mm thick foil-faced insulation. The flow-and-return arrangement can be fitted to an existing system and can be a good source of further business for a plumber if a householder later extends the house or upgrades the plumbing. Flow-and-return systems can be tricky to design if you are not doing them regularly. If you have any difficulty we recommend you contact our Customer Service on 1300 365 115. For bigger jobs, a company representative could come on-site to advise on the best system, identify the flow-line and the pump location.

PRESSURE LIMITING VALVES
Manufacturers get numerous complaints from customers and plumbers who say the Temperature Pressure Relief (TPR) valve is leaking. The problem is often the result of the water pressure at the mains not being assessed before the unit is installed. By law, a TPR valve must be fitted to every hot water service. As the water heats up, it expands; the TPR valve is designed to let out a small amount of water from the cylinder. The hot water cylinder has a maximum working pressure, which varies according to the type of system. So, TPR valves have slightly different roles and different heating requirements depending on the heater model. TPR valves can look almost identical but their pressure settings may vary considerably. Say, for example, a TPR valve is set at 1000kPa. If the town water supply coming into that property is also at or above 1000kPa, the water pressure to the unit and the valve's fail-safe pressure are the same. As a result, water will discharge through the valve all the time. The way to stop this problem is to make sure the mains water pressure is well below the TPR valve's pressure range. The cold water pressure coming into that unit should not exceed 80% of the loading of the valve rates, e.g. if the valve is rates at 1000kPa, the cold pressure should not exceed 800kPa. If the supply water pressure exceeds 80% of the TPR valve pressure, then the plumber must limit that pressure to the water heater. A pressure limiting valve can be fitted which limits the pressure going into the unit, thus alleviating the problem.