Landscape view of two brick chimneys

Does the Chimney Balloon cause damp?

As the years have gone by, we’ve talked to many different people: customers, trade representatives, engineers, and housing associations – all about chimneys and chimney draught excluders. But, despite their difference in job, lifestyle, and expertise they have one thing in common. They believed that blocking off the chimney ALWAYS caused damp.

We’re here to dispel that myth and tell you a little more about what can cause dampness in chimneys, how you can block off your chimney safely, and whether the Chimney Balloon really does cause damp.


Dampness in chimneys

Moisture is the key ingredient to chimney dampness. Without moisture, there’ll be no dampness – so getting to the source of the moisture is critical when it comes to diagnosing chimney issues.


One of the main causes of excess moisture within a  chimney is rainwater. Either through rainwater entering through a large chimney pot opening or perhaps a leak in your chimney stack, rain is the most common cause of damp issues in the chimney. Once the water enters the chimney stack it drips down the walls of the chimney and is slowly absorbed by the brickwork or lining until it starts to appear on your interiors. The more rain that enters the larger the damp issues will become so when dealing with dampness caused by rainwater it’s important to seal the source quickly.

Generally solving issues with rainwater is easy, in the vast majority of cases fitting a cowl or chimney cap will do the trick, as it’s just rain entering via the chimney pot and there are no structural issues present. However, in some cases fitting a cap or a cowl doesn’t help – this would indicate a structural issue such as a crack in the top of the chimney, issues with the lead flashing, or perhaps issues with the pointing. In these cases, we’d recommend contacting a local chimney specialist or builder for a full structural overview of the chimney and to help you figure out what’s going on.


Chimney Cracks:

Chimney cracks can present internally within the interiors of the chimney, or externally so on the outside of the chimney structure. They can be found in areas inside the home such as the chimney breast or in outside areas too such as on the chimney stack. Cracks let in moisture either from either inside the home or outside. So the moisture can come from condensation (such as cooking fumes or laundry water vapour) inside the home or from rainwater.  This moisture then accumulates inside the chimney and is absorbed by the brickwork.

These issues are a little bit harder to fix as they involve locating the cracks and filling them in with strong, waterproof material. Depending on the size and location of the crack this could be a DIY job or require a bit of professional help.


Hygroscopic salt damage:

Hygroscopic salt damage. This one is less common and only seen inside chimneys that have had frequent use but poor upkeep over the years. But, if you’re struggling to find the source of your chimney dampness it’s always worth a check. When coal, wood, or other substances are burned, smoke is produced – whilst large amounts of this are carbon and carbon dioxide some of this is other substances such as salts. These salts can coat the walls of the chimney internals and slowly penetrate the brickwork inside the chimney. Unfortunately, these salts are hygroscopic, meaning they hold water incredibly well. These hygroscopic salts pull moisture out of the air and hold it – meaning over time the walls of the chimney become moist. In cases where the salts have penetrated the brickwork quite deeply, the chimney internals can also become moist leading to dampness damage.

This issue requires specialist treatment so if you think you have hygroscopic salt damage present in your chimney we’d strongly advise you to contact a chimney specialist to assess the damage and come up with a treatment plan.


Condensation within the home is a huge issue, especially in the UK where the weather is persistently damp throughout the year. Condensation in the home can be caused by a variety of factors, whether that be lacking ventilation, excessive amounts of moisture being produced indoors from laundry or cooking, or generally leaky properties that are getting excessive moisture inside.

This excess moisture in the home often culminates with an issue in the chimney. Chimneys pull the warm, moist air out of homes up and out – but as the warm, damp air rises it is cooled the closer it gets to the chimney stack. This leads to it condensing and forming water droplets on the side of the chimney walls. If you’ve got excessive amounts of moisture in your home already, this leads to larger quantities of water droplets forming on the walls of the chimney which in turn can seep through the brickwork causing damp patches on the chimney.

Condensation is often something you can take control of yourself, by taking measures to ensure all of your ventilation systems are working well, you’re not producing excess moisture with your laundry or cooking habits, and double checking there are no leaks in your property. However, sometimes the cause does require professional input to sort.

Blocking off your chimney?

So let’s get this straight. It is a myth that blocking off your chimney causes chimney dampness or dampness within the home. Chimneys are a source of uncontrolled ventilation and their purpose was to extract waste gases from a lit fire, not to ensure there was sufficient air movement within the home. Provided you do not have issues with dampness in your home, your home has been built to building standards and has other forms of ventilation closing off that draughty chimney shouldn’t give you any issues whatsoever! If you already have a big issue with moisture in your home, blocking off a chimney will remove a source of uncontrolled ventilation from the property, this could exacerbate an already present issue.

However, if you do block the chimney and damp appears – it’s a signal that there is a bigger issue present. It indicates that you don’t have enough controlled ventilation in your home to keep moisture at bay and this is something you should check. Chimneys provide way more ventilation than a home should need to stay dry – so if you’re closing off that draughty chimney and experiencing issues you should be double checking all your vents, your roofing ventilation and airflow systems are as they should be – as there could be a hidden issue.

So, does the Chimney Balloon cause damp?

Absolutely not! As above, blocking off your chimney really shouldn’t cause any issues with dampness. Especially if your home has inbuilt controlled ventilation. Chimneys are a massive source of uncontrolled ventilation and cause a lot more air movement than is necessary within the home. You shouldn’t find blocking your chimney with a chimney balloon causes any issues with dampness. If you find it does you may have a bigger ventilation issue at hand that needs addressing.