Posted By Malcolm Greenhouse
Whilst tutoring on NEBOSH General Certificate I was asked the following question.

Why do gas fires and gas central heating boilers all require flues whilst gas ovens and hobs do not?

I said that it may be something to do with the amount of gas being burnt but I do not think I convinced the students or indeed myself.

Anyone know the reason why?

Mal Greenhouse

Posted By Norman Elkington
Malcolm

Rather than dig into specific figures and create a monster of confusion, in principle...

Input ratings of gas cookers when all burners are on may be up to 18-20kW. An adequate supply of combustion and dilution air is required even in the smallest kitchen. Think CO poisoning etc. here.
Even domestic kitchens should have inbuilt ventilation if constructed to the relevant building regulations and CIBSE guides.
From the CORGI Gas Installer Manual... "Any room containing a gas cooking appliance must have a door, window or other means of ventilation that opens directly to outside air".
There are also other qualifying room volumes imposing additional ventilation requirements.
Ventilation would have to be considered in larger industrial kitchens where extract system interlocks etc are incorporated to ensure that flue gases(products of combustion) are removed.
If an extract fan is incorporated into an existing kitchen, the 'CORGI' gas installer will test and check that sufficient air is still available to support combustion and dilute the products of combustion. Care should be taken not to allow those who are not competent (e.g. electricians installing extract fans/hoods) to disturb existing ventilation arrangenments.

I hope this is sufficient but please come back if you would like a couple of references.

Norman
(Practicing Building Services and Plant Engineer)