UK Building Regulations for Chimneys and Flues for Stoves
Suitable for heating a wide variety of different living spaces, wood burning stoves (also known as wood burners) are incredibly popular in the UK . Not only do they provide an efficient and carbon neutral form of heating, they also convey an enormous sense of wellbeing, a phenomenon which was explored by American scientist Professor Edward O Wilson in his 1984 publication of the biophilia hypothesis which suggested that human beings have deep elemental connections with the natural world, including fire.
One of the most efficient ways to heat a property, a wood burning stove or wood burner is capable of heating just a room or even an entire home, while helping to keep your energy bills low. Functional and aesthetically pleasing, a wood burning stove or wood burner also provides an attractive focal point in any living area.
This article explores how the UK Building Regulations are applied to Flues and Chimneys used with wood burning stoves and what factors determine the minimum height a flue or chimney should be.
How do short chimneys and/or flues affect a wood burning stove?
As one of the main purposes of a flue or chimney system is to remove the products of combustion (also known as “exhaust or flue gas” ) from your home, it stands to reason that your chimney must be of a certain minimum length and height to safely carry these products of combustion up into the atmosphere and not into your neighbour’s upstairs window.
The answer as to what that minimum length flue should be depends on several factors;-
What type of flue or chimney is being proposed for the building?
There are two types of flue used on wood burning stoves:
Conventional Flues
A Conventional Flue is essentially a “pipe” which allows the flue gas to escape to the outside. Log burners suffer from a phenomenon known as “chimney downdraught” (or downdraft)” which refers to a situation when the flue gas travels down the flue into your living room and fills the house with smoke. There are many potential causes for this but one common cause is a flue terminal whose location is too short in comparison with the height of the pitched roof next to it. When the wind blows from the “wrong” direction then such a short flue gets “blocked” by the positive air pressure around the terminal caused by the wind blowing onto the pitched roof.
The only solution for a conventional flue installed on a Log burner to avoid this downdraft event is to raise the height of the flue terminal so that it is much higher than the highest point of the roof.
Approved Document J of the Building Regulations stipulates a minimum flue height (stove collar to base of terminal) of 4.5m but that is the bare minimum to ensure a sufficient draught to start the fire and the stove to even operate. Many environments, situations and stoves will require longer flue heights than this to perform at their optimum efficiency and heat output.
Balanced Flues
Balanced Flues are more sophisticated than a Conventional Flue and are constructed using two concentric pipes. The smaller inner pipe carries the “flue gas” while the annulus (or ring) between the two pipes carries the air needed for the wood fuel to burn (this is also known as “combustion air”). With a balanced flue the terminal is carefully designed to achieve an arrangement whereby the point of entry of the “combustion air” and the point of escape of the flue gas are in the same location. This means that any pressure changes in the air caused by the wind have an equal (or balanced) effect on both the combustion air and the flue gas, so that there is therefore no influence exerted by the wind on the performance of the stove. It is therefore not necessary to terminate a Balanced Flue above the highest point of the house.
Other considerations in designing a flue for a wood burning stove or log burner
There are also other factors to consider in determining the minimum length of a flue such as the likelihood of the flue gas escaping to cause a nuisance to neighbours and also how far is the flue terminal from openings into your own property.
Further Information on flues for wood burning stoves
Island Pellet Stoves Ltd has been installing flues for its wood pellet burning stoves in England or Wales since 2015.
Our website has a range of resources and frequently asked questions to help you plan your project and to get the best from your wood burning stove or wood burner. Follow the link below for more information or give us a call on – 0330 111 4747