CATALOGUES AND INSTALLATION MANUALS Our catalogues and manuals contain information on our product range with detailed instructions to ensure your Metro wood fire is installed and operated correctly.
FREQUENTLY ASKED QUESTIONS Here you’ll find the answers to the most common questions our Metro stockists and customer service team are asked about our product range.
MAINTENANCE AND SERVICING Regular maintenance and servicing is important to maintain your wood fires performance, safety and longevity.
Almost all Metro fires can be fitted with a wetback to assist with your households hot water requirements and reduce your energy costs. A wetback works on the thermosiphon principle – warm water rises and cooler water falls, creating a natural flow through the wetback circuit. A minimum gradient of 1:12 for the hot water supply pipe from wetback to hot water cylinder is required for the water to naturally circulate. The hot water cylinder should be close to the wood fire to minimise heat loss. Performance of a wetback system can be affected by the quality and type of fuel being burnt, the amount of time the fire is operating, the distance between the fire and hot water cylinder and the air control setting. It is beneficial to find a plumber who is experienced with wetback installation to maximise all efficiencies.
Typically, the hotter the fire burns, the more hot water the wetback will produce. To optimise hot water production, a heat transfer system to transfer excess heat from the living area to the remainder of the home will encourage a higher fire setting for longer periods. In return this will result in a fantastic ambient throughout your home and more hot water being generated by the wetback. It is a good idea to contact your local building consent authority for any particular requirements or advice they may have about wetbacks. You will need a building consent to install a wetback and the work must be carried out by a certifying plumber to meet the National Standard AS/NZS 3500.
‘Direct’ open circuit systems (low pressure) are more efficient than ‘Indirect’ closed loop systems (mains pressure) where the heated water has to pass through a coil (heat exchanger) to transfer energy from the wetback into the potable water within the storage tank. Low pressure copper wetback cylinders are New Zealands traditional wetback hot water cylinder but there are now more ‘Indirect’ systems being installed as mains pressure systems are now very popular.
‘Direct’ wetback circuit
All water is low pressure. The system is either gravity fed by a header tank in the ceiling or a pressure reducing regulator is required to lower the water pressure in the system. As water is heated in the fire’s wetback, it rises within the low pressure copper cylinder. Cold water then replaces the rising hot water within the circuit. This cycle continues until the cylinder is heated. This type of system is a ‘direct’ open system, meaning the water used in the home is running through the circuit and wetback system. Pressure created by the rising temperature is vented through an open pipe, usually above the roof of the home, instead of a temperature pressure relief valve (TPR valve).
‘Indirect’ wetback circuit
All consumable water is high pressure, but the heating circuit is open vented low pressure. While the home uses mains pressure, the wetback circuit is a separate low pressure system where the energy is transferred into the mains pressure hot water tank via a coil (heat exchanger). This system works in a similar way to the low pressure copper cylinder but uses a closed water circuit between the wetback fire and cylinder. As water is heated, it rises through this circuit and through a coil in the cylinder. Heat is transferred via this coil into the useable water in the cylinder. A storage tank with a long heat exchange coil is therefore far more efficient than a tank with a short coil.
This system is not as common but has benefits over other systems by not having any significant storage volume of potable water. The system operates like an instantaneous heater where the filled tank is simply a heating medium where heat is transferred into the mains pressure water as it flows through a long coil within the tank. These systems need to be sized correctly to ensure there is sufficient capacity to heat the water as it flows through the inner heating pipe. Just like an instantaneous heater if water flows too fast through the heater it will cool off until such time the flow reduces, and time allows energy to re-absorb back into the water being heated.
Please note: Wetback system design and all plumbing work must be completed by a certifying plumber to meet the national standard AS/NZS 3500. Hot water supply via a wetback system must be tempered to ensure safe operating temperatures to all fittings and fixtures.
