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Why Size Matters

It’s all too easy to think you know all there is to know about installing flues. After all, you’ve been doing it for years.


There are, however, a number of questions that we get asked time and time again, including: how close can a flue be installed to a window? How long can the flue be? And, what is nuisance pluming?


To help you site it and size it right on every job we’ve put together a quick guide that you can refer back to anytime.


Why size matters


All of Baxi’s, Main’s and Potterton’s system or combi boilers with a 60/100mm concentric flue fitted can be up to a maximum length of 10 metres. If you find that you do need a longer flue run, then the flue size can be increased to 80/125mm, giving you a maximum flue length of up to 20 metres.


Operating a boiler with a flue that exceeds the maximum length could result in the boiler not working as it should. The ignition could be delayed and the combustion affected, resulting in serious damage to the boiler. Who said size doesn’t matter?


Providing adequate support


BS-5440 requires that flues must be properly supported throughout their entire length. Baxi specifies a support must be used at least once every metre, and provides the brackets to make it easy to comply.


Site it right


There are multiple siting considerations when installing a flue, to prevent harmful flue emissions from re-entering the property or those nearby. For instance, a flue terminal must be a minimum distance of 300mm from an opening window. Remember however, that plume displacement kits are available which means you can site the flue terminal air intake at a minimum of 150mm from an opening window or door.


If you’re unsure about any of the siting distances, always check the manufacturer’s instructions.


Preventing a nuisance


BS5440-1 states that the flue shouldn’t be installed where it’s likely to cause a nuisance; one such example could be a condensate cloud pluming above a neighbouring driveway. To avoid this, the distance from a fanned draught appliance terminal, installed next to the boundary line, must not be less than 300mm. However, the use of a plume deflector can reduce this minimum to 25mm.


Every installation is different. You should always pay close attention to both siting and sizing of the flue to avoid damage to the boiler and causing a nuisance to neighbours.


To find out more about Baxi’s range of flues and accessories, please visit here. 

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