Log Burner Ventilation: Why Do I Need an Air Vent?

Log Burner Ventilation: Why Do I Need an Air Vent?

I’ve ordered a new multi fuel or wood burning Stove to keep the house toasty but my fitter says I need an air vent. So now I want to know:

  • What’s the point of spending all that money on a stove if I’ve got to make a great big hole in the wall?
  • Won’t an air vent make it colder than before?
  • Surely it will be draughtier?
  • Can I have the stove without cutting a hole in the wall?

Good questions. Let’s see if we can answer them, first of all the science bit about how fire and chimneys actually work….

Why Do Log Burners Need Ventilation?

Fire is a chemical reaction when fuel (wood or coal) and oxygen in the atmosphere are ignited. Without sufficient amounts of either fuel or oxygen the fire will gradually go out. Chimneys work when an up-draught caused by the difference in temperature between the gases from the fire and the atmosphere outside draws the air up through the flue. At the same time fresh air for combustion is drawn into the stove.

If too much air flows up the chimney your house will start to depressurise. When a space becomes depressurised it wants to replace the air from any available source – through windows or doors or even from the chimney. This causes the smoke to come back into your home rather than escaping as it should.

So the main reasons for needing a vent are: To fuel the fire, and so that smoke from the stove escapes through the chimney and doesn’t come back into the room.

Ventilation Requirements for Wood Burning Stoves – Do You need One?

You might be wondering whether it is just advised that you have ventilation for your stove, or if it is a legal requirement.

There are a number of wood burning stove regulations that all log burners have to conform to. If yours doesn’t, you won’t receive a certificate of compliance, and you will have to pay a fine if you don’t correct it.

Don’t worry though – if a HETAS installer does your job, they are trained to ensure yours is up to standard!

So, back to air ventilation – there are a set of regulations in place covering air vents for stoves.

However, these requirements depend on one thing – the air permeability of your house. This is, in layman’s terms, a measurement of how airtight your home is. The more airtight your home is, the less permeable it will be.

The Air Permeability Rule for Log Burners

The air permeability of your home affects how much ventilation you will need for your wood burning stove.

Houses built after 2008 are required to achieve an air permeability of 5 m3/hm2 or less. This is because it makes home heating much more efficient and reduces energy wastage. Houses built before 2008 weren’t required to meet this goal, so houses that are very old may have a much higher permeability rating.

If your house was built before 2008 and you are unsure of how airtight it is, you can get it tested by a professional – your stove fitter can often do this for you, too.

If your home has a permeability of 5 m3/hm2 or more…

  • This is likely to be an older home built before 2008
  • Ventilation is not required for a stove with a heat output of less than 5kW
  • For a log burner over 5kW in heat output, you will need 550mm2 of ventilation for each additional kW

For example, a 5kW stove would require 550mm2 of ventilation.

An 8kW stove would require 2,220mm2 of ventilation.

If your home has a permeability of 5 m3/hm2 or less….

  • This is likely to be a post-2008 new build
  • Ventilation is required for any wood burner you install
  • You will need 550mm2 of ventilation per kW of your log burners heat output

For example, a 5kW stove would need 2,750mm2 of ventilation.
An 8 kW stove would need 4,400mm2 of ventilation.

Here is a reference table to help you out…

Log Burner Heat Output
Ventilation required for
home permeability of
5 m3/hm2 or more
Ventilation required for
home permeability of
5 m3/hm2 or less


How Do I Ventilate My Room For a Log Burner?

You won’t need a great big hole knocking through your wall!

The lowest amount of ventilation, 550mm2, is roughly the size of a 50 pence piece. Many older homes don’t need a vent at all – a 5kW stove is quite often enough to heat a room up to 5M x 5M; that’s over 16 feet square.

Air vents can seamlessly fit into your wall, often in the form of a brick with a tube connecting your room to the external air. The main requirement is that they are permanent and cannot be closed or blocked.

Alternatively, many stoves have optional external air kits. These vent air straight from the stove box to the outside air, so you don’t have to worry about positioning one in your room.

A correctly fitted air vent shouldn’t make the room colder, you probably won’t even notice it’s there when the stove isn’t in operation. There will be a flow of air from the vent to the stove when it’s in use, so think about your room layout. Don’t have the vent positioned just behind your favourite armchair as you will notice the airflow once the stove is lit.

Where should you place your air vent?

The main thing to bear in mind when positioning your air vent is the draft they can create. For this reason, try to place it as close to your stove as possible. Don’t put it anywhere that could cause an unwanted air flow – such as across the floor of your arm chairs or dining table.

Remember, your stove will give off plenty of heat, so don’t worry about the vent making your room cold!

Still having trouble?

If you find your stove is struggling to perform properly – such as the smoke is failing to rise out of the chimney, or the fire isn’t burning strong enough – incorrect ventilation could be the issue.

Try opening and closing your windows and doors while your fire is burning. If this makes a difference, it may be that you need more ventilation.