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Why should I fit a Low Loss Header? 1. Your boiler, particularly the heat exchanger in you boiler, will only function at it's peak efficiency when the water velocity passing through it is maintained within prescribed parameters. Boiler manufactures should tell you what the specs are for each make and model. In some cases the flow rate through the system circuit will exceed the maximum flow rate through the boiler, or it may be that the system flow rates are simply unknown. In other cases the reverse is true, where the boiler flow rate exceeds the maximum system flow rate (particularly true in some multi boiler systems). Fitting a Low Loss Header allows the creation of a primary circuit, within which water velocity can be maintained at the required constant, regardless of changes or requirements in the secondary circuits. 2. Not only is the water velocity important, but also water temperature. There are two potential problems: the first is "thermal shock". If the temp difference between the flow and return is to great, it puts a huge strain; through thermal expansion and contraction, on the heat exchanger. Also the temperature of the water passing through the heat exchanger is important, particularly with condensing boilers, these have there own specific requirements to operate at maximum efficiency. For a boiler to go into "condensing mode" the return temperature should not be higher than about 55'C. So in some cases temperature sensors are fitted on the header to allow control over the primary circuit temperature. 3. Because of the reduced water velocity, the header is an ideal place for siting an automatic air vent for removing air and a drain point for removing sediment and debris. These are generally fitted as standard on most headers 4. The header allows separation of primary and secondary circuits for easier diagnosis when problems occur.