Stove with Chimney ‘Pipe’ Smoking Back? Here’s 5 Common Reasons Why…

You can have a chimney pretty much anywhere these days thanks to twin wall insulated systems.

These factory-made flues negate the need to build an expensive, brick chimney and are quicker to install.

However, they aren’t without their issues if they’re not operated or installed correctly.

Here’s the 5 most common issues

#1 – Cold Flue Syndrome

This usually happens when the flue goes through the wall and up the gable end of the property. The reason is pretty simple; despite being insulated they can, by virtue of their position on an exterior wall, get pretty cold. So they can struggle to ‘draw’.

The best way to counteract this is to warm the flue for a few minutes before starting a fire.

This could be with a small camping stove, a heat gun or maybe even a few firelighters (although these can create the smoking back you’re wanting to avoid).

Once warmed for a few minutes, I would then advise using the ‘top down’ burning method to, again, help warm the flue further but also ensure you create the minimum amount of smoke.

Below is a video I did on this a while back. Try it for yourself…

#2 – The Flue Isn’t Tall Enough

For any chimney to work, the flue terminal needs to be a certain height. That height all depends whereabouts it is in your property.

Building regulations have very specific guidance on how far terminals should be from opening windows, adjacent structures and the weather surface of your roof.

Unfortunately I see very many twin wall systems which aren’t tall enough.

This is mostly to do with fitters who don’t want to add scaffolding or additional supports onto the final bill, so they terminate it too short – usually below the apex of the roof.

When this happens it can affect the performance of the installation. So make sure it’s done properly first time, as per below.

#3 – Too Many Bends

Similar to the previous point, Building Regulations have set parameters for flue design and yet I see some very unusual set ups.

A common issue can be excessively long horizontal runs from the back of a stove followed by a 90 degree bend upwards towards the remainder of the flue.

Other designs may have an excessive amount of bends in the flue, causing the chimney not to function properly.

Ideally, you would want a pipe coming off the top of your stove and then having no more than four 45 degree bends before the terminal.

If the pipe is coming off the back off the stove, there are certain rules and calculations needed, depending on the length, in order to prove it works, and that the manufacturer has given consent.

While this may all sound a bit technical, the net result could be, again, that the flue smokes back. So it pays to ensure it’s to regulations.

#4 – Lack of Ventilation In the Room

Because twin wall systems are more common in newer properties (or extended parts of older properties), ventilation can be an issue.

The science is quite simple; stoves need air in order to ‘work’. The newer the home, more likely it is to be ‘airtight’.

Better wall and roof insulation, modern double glazing, extractor fans… they all have the ability to cause issues for a stove.

It’s worth pointing out here that any home with a solid fuel appliance built after 2008 must, under building regulations, have an additional air supply. This is to ensure the stove works properly.

#5 – Design of Stove

Because of a lack of chimney breast, many people want, or are to choose, larger stoves to compensate for this.

These stoves tend to have very large doors and, when refuelling, they can ‘spill’ smoke into the room.

Smoke will generally follow the path of least resistance, so when you open the door, it may – if the pull outwards into the room is bigger than the pull upwards into the flue – cause smoking back.

My advice is to crank open the door to a larger stove slowly, and when refuelling only do so by opening the door a quarter of the way.

That way, you’re not giving the smoke as much chance to escape and keeping the draught in the stove and flue more evenly balanced.


When done correctly, twin wall insulated systems can be fantastic and give many years of happiness. Done incorrectly and it can turn into a thoroughly miserable experience.

If you’re having problems with your own twin wall insulated chimney, you’d be wise to contact your local, professional chimney sweep.

As people who see stoves and flue systems regularly, we can usually pinpoint these issues fairly quickly.

And of course we can provide you with the advice and guidance you need to help remedy the situation as soon as possible.

Mr Soot Chimney Sweep is a HETAS Approved Sweep, and member of the Guild of Master Chimney Sweeps, offering a professional and friendly chimney sweep service. Book Mr Soot online or call 0800 0541154.

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