Chimney sweep video advice – does my fire need an air vent?

Video Transcription

(Slightly edited for better reading)

The Heat Triangle – Fuel, Air and Heat

Lee Pearce: air is a necessity for all fires. All fires when they burn – if you can imagine, when you were back at school, the heat triangle: you need fuel, you need oxygen and you need heat; to make a fire. Take one of those three things away and the fire doesn’t burn. As oxygen is only 20% of air, then if you want one volume of oxygen – you need 5 volumes of air, imagine it in buckets, to get one bucket of oxygen, you need five buckets of air.

When fires don’t burn properly

If the fire doesn’t burn properly, you get incomplete combustion. Which means it’s going to produce more carbon monoxide and nasty gasses that we do not want. If carbon monoxide comes into the room, it is very dangerous and should be avoided at all costs.

If you’re not burning the fuel correctly, then you’re not getting the right economy (value for money) for the fuel you burn; you’re not getting enough heat from the fuel you’re burning; you’re not being as warm as you should be. Plus, what’s going out of the top of your chimney is more carbon monoxide and gasses which are harmful to the environment. 

What all fireplaces need

All fireplaces, no matter what fuel you burn, need air. With a gas fire, especially with decorative fuel effect gas fires an air vent is required, usually if its over 7.1 kw input, if its under that it probably wont require an air vent. The manufacturers instructions will detail the requirements.

All solid fuel open fireplaces need an air vent and the size of the air vent should be 50% of the throat opening to the chimney.

air vent london

Air Vent

Wood Burning Stoves

In the case of a wood burning stoves and room heaters, if the appliance is under 5 kw normally you won’t need an air vent. But if it’s over 5 kw you do need an air vent. If the houses was built before 2008, the air vent size would need to be 550mm2 per kW over 5kW. So for an 8kW appliance an air vent of 1650mm2 would be sufficient. If the house was built after 2008 (and so is much better insulated) the air vent size is calculated at 550mm2 for every kW, so for an 8 kW appliance an air vent size of 4400mm2 would be required.

All open fireplaces burning solid fuel (smokeless coal, coal or wood) need an air vent. I would say 80% of my customers don’t have the correct ventilation in their properties, it is very difficult to convince some people of the necessity of an air vent, especially as it has to remain permanently open.


Please contact Apex Chimney Sweeps London if you’d like to discuss chimney and fire safety.

More related info:

Chimney Smoke Testing
Complete Chimney Safety Inspections
Chimney Sweeps London