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Why do I need to sweep my chimney?

People who are new to solid fuel fires may not be aware of the importance of having a clean, swept chimney. After two or three generations of families used to gas fired central heating boilers the idea of a chimney sweep belongs to another era.


Firstly, all heating devices that use a chimney or flue to exhaust the products of combustion to the outside should be swept regularly; this includes gas, oil and solid fuel type heating systems. But solid fuels (coal, smokeless fuels, wood, peat etc) are more prone to fouling of the chimney, due to their incomplete combustion process.


This fouling, usually seen as soot or sometimes tar and creosote, is made up of unburnt particles of fuel and can be seen leaving the chimney as smoke. If it all leaves the chimney as smoke, other than wasting energy and polluting the environment, no harm is being done. Unfortunately some of the smoke will condense on to the walls of the chimney and begin to build up in layers. The rate this occurs depends on a number of factors; cold chimneys, high moisture content in fuel, slow burning of fire, already fouled flue and air leakage into the chimney or poor draw.


The important phrase here is “unburnt”, this indicates the layer of soot or tar is still combustible and can catch fire in the right circumstances. Anybody who has witnessed a chimney fire would not want to repeat the experience. Temperatures of 1000 deg C are possible in the chimney and damage to property, including setting fire to the living space can happen.


The chimney of any solid fuel fire is the driving device, the fan, engine, motor of the system, it is the chimney that pulls in the air to the fire so that combustion can take place, once the combustion is completed it draws the exhaust from the fire/stove and pushes it 10m or so up a narrow duct and safely out of the home. It does this with no moving parts and entirely automatically. So why would we want to make its task more difficult by allowing it to be constricted with a build-up of combustible, black, dirty, smelly material.


As a chimney sweep we often visit peoples home and are told that the fire has been leaking smoke for a couple of months, but only a little bit when we first light it and it goes away after half an hour or so. Usually the ceiling is stained light brown and there is a funny smell in the sitting room. We can live with staining and smells, but not with the carbon monoxide gas which is contained within the escaping smoke. Carbon monoxide (CO) is a colourless, odourless and tasteless gas which is toxic to humans and animals. It will kill you in high enough concentrations, first the pets die, then the children and finally the adults.  A CO alarm is cheap and easy to fit and will give you more than enough time to vacate the room. Using the services of a professional chimney sweep should stop you having to face that situation.


The National Association of Chimney Sweeps makes the following recommendations for sweeping a chimney in normal use:


Chimneys with solid fuel appliances – Smokeless fuels at least once a year / Domestic bituminous (house) coal at least twice per year.


Chimneys with wood burning appliances – Quarterly when in use.


Chimneys with gas or oil appliances – Once a year.


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