Combustion ventilation – don’t get caught out

Jun 10, 2016, 17:04 PM by FENSA


Mention gas appliances and installers usually shrug their shoulders and say it is nothing to do with them. They could not be more wrong! There are a couple of instances where not taking notice of a flue or vent may land you with a failed inspection, or even worse, a trip to court.


First up is the combustion vent. This is a vent that is permanently open and usually looks like a plastic cone on the glass with a free spinning fan inside. Sometimes they are vents that were once closable but a gas engineer removed the cords long ago. This vent needs to be permanently open so the appliance can get enough oxygen to burn efficiently. If it does not burn efficiently then it will produce too much carbon, which will soot up flues leading to a blockage. If not spotted this could result in carbon monoxide spilling back into the property – with possible deadly effects! These vents are only used when the appliance takes its oxygen from within the room – such as back boilers. Modern balanced flue boilers do not need them. If the old boiler has been removed and a new room-sealed appliance installed then you can take away that permanently open vent and replace it with a new solid piece of glass. Unless you are completely confident you can proceed, you must always seek confirmation from a gas safe engineer. Ignorance is no defence in law.


Next for discussion are the flues themselves. Flues have usually been installed to the regulations that were applicable at the time. They would have been positioned away from openings so the exhaust gasses do not immediately flow back into the building. For window installers to comply they must not move any opening closer to the flue than is acceptable under the current regulations. Where installers seem to get caught out is in buildings constructed in the 1980s and 1990s where the boiler was installed in the corner of the kitchen next to a window. The window is usually a fixed pane next to the boiler with a side hung opposite. At time of sale of replacement windows the householder explains that they cannot easily reach the window to close it – as the handle is half way up the opener. So a decision is made to convert the window from a half side hung to a full top hung. This is great for closing but you have just moved the opener right next to the flue and this does not satisfy current regulations! Remember if in any doubt about gas appliances you can consult Approved Document J (available as a free download on the Planning Portal website) as this will give you correct distances from a flue as well as minimum ventilation requirements. An even safer bet is to talk to a gas engineer.

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