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Central Heating

Central heating boiler vents

My elderly mother has a central heating boiler in a cupboard in the middle of the house. The exhaust gases are expelled via a pipe which goes out through the roof. There are pre-existing vent holes from the kitchen into the cupboard. I am sorry, I don't know what boiler she has except its not a combi-boiler.

She has been told by several plumbers that the size of the vents needs to be increased. And that, additionally, either the boiler has to sit on an outside wall or a vent has to be cut into the outside wall (not practical as she suffers from the cold and has multiple health conditions).

What I am not clear on is:

- why direct venting to the boiler is a requirement; and

- whether this could be achieved via a flue which allows fresh air and exhaust gases along the same pipe (albeit in different sections).

Any advice or thoughts would be gratefully received.

Many thanks

4 Answers from MyBuilder Heating Engineers

Best Answer

the type of boiler that you have draws the air for combustion from the surrounding area so provision for this must be provided by vents etc. if the boiler is on the ground floor and if the ceiling joists run towards the outside wall it would be possible to fit a vent in the cupboard ceiling and an air brick in the outside wall, this should be sufficient, my boiler fitted some 20 years ago in an upstairs cupboard has a vent in the floor behind the boiler and an air brick,hope this helps, regards Terry.


Answered 4th Jun 2011

Hi, In response to your questions.

The twin flue, 'Balanced flue' you have suggesested is commonly used on certain appliances.

Though you do not site, make model etc, of boiler it clearly a conventional flued appliances. (Using oxygen from the surrounding atomosphere), to achieve complete combustion.

In short, its very much like putting a glass over a candle, the candle will extinguish.

If you were to partially cover the candle with a glass, then the glass would blacken, carbon monoxide !

Without adequate ventilation, for the boiler to burn there could be incomplete combustion, (Like the candle / glasss senario).

Carbon monoxide is colourless and in the main ourdourless. I would suggest that if adequate ventillation is not put in place then your elderly mother could indeed be at a far graver risk then merely feeling the cold !

I would suggest, at a very minimum you install two carbon monoxide detectors to the property. One outside your mums bedroom door and one outside the boiler cupboard "

Kind regards,

Adrian Hagger


Answered 4th Jun 2011

It sounds like the boiler is open flued and so needs these vents to be able to burn gas properly (complete combustion). If this is so your mother does indeed need the vents to be larger and some outside air to be introduced. There are strict rules detailed in the installation guides which are available from the manufacturer.
If draught is really a problem then you will have to consider changing the boiler to a modern fan flued version which sucks it's oxygen in from the outside. This type of boiler wont need any vents.
You should have a decent (£20) carbon monoxide alarm fitted for her too.


Answered 9th Jun 2011

The boiler make and model details would be required to give a good answer. However.....

Is the boiler open flued? If it is, the boiler takes air for combustion from the room/cupboard it is installed and therefore the ventilation has to be correct to allow the correct amount of air in. If it is not open flued, the ventilation is just for keeping the boiler cool. As for your question about using a flue, again if the boiler is open flued then no you cannot fit this type of flue and if it is a room sealed boiler it already has this type of flue.



Answered 4th Jun 2011

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