Regardless of if you are building or renovating and if your property has a chimney you’re going to want to ensure that it works as it should. Chimneys do not just add a huge amount of character to a home, but they are also crucial if you want to enjoy the warming joy of a wood burning stove. This guide is designed to explain everything you need to know about chimneys and flues and how to make sure you’re safe and functioning.

Why do We Have Chimneys?

Despite holes in the roof and walls of older homes, it is evidence that our ancestors knew it was important to get smoke out of their homes, chimneys were not really widely adopted until the Tudor times, and even then, only by the upper classes, with more common people having to put up with smoke-filled rooms.

Even when chimneys were used more frequently, they were extremely inefficient and could often be dangerous too as they were often made of wattle and daub and susceptible to spreading fire. By 1710, all clay-built chimneys in England were ordered to be rebuilt from brick.

However, a distinct lack of understanding of heat and smoke indicates that chimneys can still not draw in the way they should, and it wasn’t until the mid-18th century where the likes of Benjamin Franklin who was referred to as The Universal Smoke Doctor, Charles Willson Peale and Benjamin Thompson, known as Count Rumford, led the way to change.

Count Rumford created a fireplace and chimney made to decrease the smoke pollution in London. The new Rumford fireplace forced heat back into the roof, with the chimney being incorporated into the wall itself.

How do Chimneys Work?

At the bear minimum it’s important that a chimney works properly and is safe. Firstly, you need to know what makes a chimney work. Basically, you’ll want to know, why does the smoke go up the chimney rather than drift out into your house? Well, the upward motion of air and smoke in a chimney is referred to as the draft. Draft takes place due to the physical fact that hot gases are less dense than colder gases. The heated gases in a chimney are lighter than the air in the atmosphere which in turn makes them draw up into it.

Fundamental Fireplace and Chimney Maintenance

There are a few fundamental maintenance factors to consider in regards to chimney care and here we list a few of these key pointers for you:

• Have your chimney swept regularly by an experienced chimney sweep.
• Be sure that the chimney is safe and in good working order when prior to usage.
• Check the carbon monoxide and smoke alarms frequently.
• Fit both if they are not already put in place.
• Factor in that chimneys are impacted by erosion from the inside because of the corrosive impact of flue gases.
• Always burn dry, well-seasoned wood, otherwise tar deposits may collect within the flue.
• Inspect chimneys externally as they tackle the full force of the year-round weather.
• Look for loosened chimney pots, eroded mortar on the stack and defective flashing where chimney and roof come together.
• In the roof space check for dampness around the chimney stack.
• When buying a salvaged fireplace take precise measurements to make sure that all the parts fit together.
• Regularly clean your fireplace, clearing ash and debris from the grates.
• Fill in any cracks and gaps that you notice in the fireback and surround.
• Clean and polish decorative elements.

Common sense may indicate that a taller chimney creates more draft due to the simple fact that there is often much hotter, lighter gas in it, which produces more updraft. Moreover, the increased draft inherent to a taller chimney tends to be offset by the greater friction found in the chimney and by the tendency of the gases to decrease in their heat as they rise. A dirty, roughly-lined, tall chimney is subject to ineffective insulation and potential air leaks could well be less efficient than a well-designed short chimney.

Physics also happens to be a factor in the functioning of chimney performance. As air is blown from the end of a tube, a drop in pressure is created at the end of the tube. Wind blowing over a chimney has a similar effect, adding to the draft.

For a chimney to work as it should do, it is required to have a good flow of air and for the flue to maintain as high a temperature as possible, so, there are exacting Building Regulations about specific chimney design. For example, it’s crucial for chimneys to be insulated, as this ensures the smoke is warm and decreases the chances of it condensing as tar deposits. This is very important with wood burning appliances, as they burn cooler than coal.

Warning signs of chimney maintenance problems

A fire within a fireplace or stove should burn well with smoke and fumes being carried away via the flue. A chimney must be swept at least once a year by a qualified chimney sweep and more often if fires are lit often. A good company that specialises in chimney maintenance will be able to advise on potential problems.
Various early signs to look out for:

• Twigs in the hearth from a bird’s nest.
• Plaster, brick, stone or soot debris coming down the chimney.
• Poorly burning fires.
• Smoke coming into the room.
• Recurring sooty smells.
• Damp patches or staining appearing on chimney breasts.

Common significant defects to look out for:

Smoky fires

There are quite a few reasons as to why smoke can gush into the room instead of rising up into the flue as it should. A distinct lack of air is a common cause. Open fires require at least six changes of air in the room every hour to burn as they should. To check if bad air starvation is the issue, try opening a door or a window, if the smoke clears then the solution is to increase air supply, for example by installing vents or underfloor ducts.

Smoky fires can also be triggered by chimneys being blocked by debris or nests, hence the importance of regular sweeps. Smoke may occasionally be blown back down by downdraughts where a chimney is too short or overshadowed by surrounding high rise buildings, trees or hills. Short stacks could be built up or extended by fitting specialised cowls or pot extenders.

Fire burns weakly

Where a fire may struggle to burn, it could choke on exhaust gases that are not totally dispersed. This may be due to a poor airflow or because of a downdraught. Problems with indoor air supply are frequent in houses where draughts have been totally sealed up so there’s just not enough air being sucked into the fireplace. These solutions are as described in the above section for smoky fires.

Smoke and fumes leaking into different rooms

Air leaks through defective brick joints can permit toxic smoke and fumes to seep into different rooms. Leaks can be traced using smoke pellets. Test for leakages using a smoke pellet bought from a fireplace shop or plumbers’ merchant. Where possible, temporarily seal the top of the flue, however, scaffolding will generally be required for access. Light the pellet in the hearth and then examine the whole length of the chimney, including the loft space, for smoke leaking out through any of the masonry. The solution is to have the flue professionally lined.

Chimney fires

Over the years, excessive soot and tar could build up on ledges inside a flue, which could eventually ignite. Flues need to be swept once a year to remove combustible soot deposits and blockages, particularly if burning green unseasoned wood or peat, which are often aggressive fuels.

Birds entering the house

Unprotected chimney pots may permit bird’s to have access and start nesting. The solution is to fit a special protective bird guard into the chimney.

Here at James Dunn Roofing, we know it can be very easy to overlook chimney damage. However, the consequences could be disastrous. From falling parts to perished brickwork and falling tiles, there are many reasons to book a regular chimney service. If your chimney has aged or you suspect weather-related defects, the team at James Dunn Roofing Ltd can help. From a simple chimney repair to a complete rebuild, we have the knowledge and skills to deal with your chimney. Based in Oxford and servicing clients around Oxfordshire, we provide free quotations for all your chimney needs. To find out more, please get in touch with us today.