Depending on the boiler model and the type of flue, the maximum length could be between 8m and 14m total, less any deductions for use of bends. The specific allowance for bends is 1.3 metres of flue length for each 90-degree bend and 0.9 metres of flue length for each 45-degree bend. The total maximum equivalent flue length is always shown in the boiler instruction manual of every model.
If a flue exceeds the maximum length, then the boiler may not function as it should and could result in serious damage to the boiler, for example, if the ignition is delayed and the combustion is affected.
What do I need to know about boiler flues?