Why does smoke come into my room?

If smoke comes back into the room when your fire is lit your chimney is not working properly and this means gases like carbon monoxide are entering the room. Carbon Monoxide can cause serious illness and even death so you must get the problem rectified immediately.

It is essential we correctly identify what is happening before we go through the solutions.
Is the smoke coming in as small puffs of smoke or is it continuously coming in?
These are two very different problems with different solutions so we have reviewed them separately below. Simply click a link to read more.

Small Puffs Of Smoke Coming In Every Now And Again

This is caused by what is known as ‘downdraught’, i.e. when when air is blown back down the chimney.
Downdraught is usually caused by a chimney that is either not high enough in relation to the building it sits on and it’s position on that building and/or other nearby building or trees that affect the wind currents around the chimney. This problem is often intermittent, worse on windy days when the wind is in a certain direction.

Smoke is not only dirty, it contains gases and particles that are dangerous to your short term and long term health, including carbon monoxide (CO) gas which is deadly in large enough quantities.
You absolutely MUST get this problem fixed.

The simplest solution is to raise the height of the chimney either by changing the chimney pot to a taller one or perhaps by extending the chimney stack, i.e. building it higher. Another solution is to place a special anti-downdraught cowl on top of the pot. The issues we find with cowls are;

  1. if they are not fitted properly they can be knocked off during sweeping and
  2. it is sometimes difficult for a chimney sweep to clean the top of the chimney as well as they might if there was no cowl. Any lid on top of the chimney pot stop the chimney sweeps brush from moving freely and cleaning as effectively.

There are building regulations in place today that specify the height and position of a buildings chimney to ensure it is safe for the property and its occupants. You can find more details on our ‘What Height Should My Chimney be?’ blog. If you live in an old house your chimney might not meets today’s safety standards so it is worth checking with your sweep what the best course of action is.

Smoke Continuously Coming In

There are a variety of reasons that could cause continuous smoke, but it is unlikely to be caused by downdraught (the main cause of small puffs of smoke.) The main culprits are listed below and there may be more than one of these at work. Click on each one to expand.

Smoke is not only dirty, it contains gases and particles that are dangerous to your short term and long term health, including carbon monoxide (CO) gas which is deadly in large enough quantities.
You absolutely MUST get this problem fixed.

Blocked / Un-swept Chimney
As soot builds up in the fireplace, flue, chimney stack and chimney pot it restricts the size of the flue which causes smoke to move slower through it. This can causes smoke to build up and back up as there is more smoke than the chimney can handle. Other blockages and debris such as birds nests or falling masonry can cause blockages that restrict the flue opening. Simple solution is have your chimney swept regularly.

Problem Chimney Pot or Cowl
Some chimney pots and cowls are just not suitable for chimneys with working fireplaces or stoves. They can restrict the ‘termination point’ of the chimney which means smoke can’t out quick enough and can build up and back up down the chimney. Ideally you want a pot that is straight and does not narrow. It is often difficult to know which type of cowl is suitable for your circumstances so ask your sweep or check our Pots and Cowls page.

We regularly see unsuitable cowls on chimneys and we ourselves don’t use cowls at home, they don’t always work and can get in the sweeps way. Older buildings were designed so rain water falling down the chimney would soak into the bricks and mortar and then evaporate away. This relies on good ventilation, i.e. air is able to flow through the chimney when the fire is not in use.

Poor Ventilation
All fires require air to work properly. As the fire burns air is drawn from the room into the fireplace. Usually air enters a room through vents and gaps in doors and windows. If there is not enough ventilation coming into the room there is not enough air to pull into the fire and the result can be a sluggish burning fire and smoke coming back into the room.

To check if ventilation is a problem, when the issue occurs open the door to the room and open a window in the next room to create a good air supply that can flow freely to the fire. If the problem improves then you know ventilation is at least partly to blame and you need to review the ventilation in your room or keep a window open slightly in the room while the fire is lit.

Chimney Height & Position
The height of your chimney, its position on the roof and the height of other buildings and trees etc in close proximity to your chimney can all affect its performance and can be a cause of smoke coming back into the room. Generally the higher the chimney the better but air pressure changes, wind and eddies caused by the wind changing direction due to higher buildings can push air and smoke back down the chimney.

Current building regulations give directions as to the height chimneys should be built for fires to be used safely. Many chimneys in use today were built decades or even centuries ago and todays building regs can be used to help determine if a chimney is sufficiently high enough. We have summarised details from the regs on our FAQ ‘Is My Chimney Tall Enough?‘ and you can find a link to the regs themselves.

Size Of The Fireplace Opening
If the size of the fireplace opening is too large in relation to the size of the flue, the performance of the chimney can be affected and the result can be smoke coming back into the room rather than being drawn into the chimney. This should not cause a problem for stoves as long as they have been fitted properly – with flue pipes appropriate to their size. This can be a problem for open fires, particularly if a decorative fireplace has been removed effectively leaving the ‘builders hole’ as the new fireplace.

Current building regs state that an open fire with an opening size of up to 50cm by 55cm (total area 2,750cm2), requires a round flue size of 20cm diameter or a square flue size of 17.5cm by 17.5cm (total area 306cm2, or appropriate dimensions for a rectangular flue to match the total area size of the square flue).

If the fireplace opening is larger than 50cm x 55cm the flue size should be equal to 15% of the opening size.
Example: An opening size of 60cm x 70cm (total area 4,200cm2) requires a flue with an area of 630cm2 (15% of the opening size), equivalent to a square flue size of 25cm by 25cm.

If you think your fireplace opening is too big and may be the cause of smoke entering the room, you can test the theory by temporarily reducing the opening by fixing a non combustible material across the front of the fireplace opening at the top, thereby making the opening smaller. If the smoking stops than you know the opening size is at last part of the problem. It’s relatively easy to increase or decrease the size of the fireplace opening and a reputable builder should be able to help with this. Decreasing the size of a flue can be achieved with a lining although this can be expensive. Increasing a flue size is far more difficult and would require major work.

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To Book A Professional Chimney Sweep In Brighton & Hove, Get In Touch Today To book a chimney sweep appointment, call us on 01273 726 989 or 07742 829 848. Alternatively you can book online using our simple Online Booking Tool. It is quick and easy to use, you can select the date and time that suits you and pay securely with a debit or credit card via PayPal. Stay safe when using your fire or stove, keep your chimney clean!