Flue Systems

flue systems

What Is a Flue System ?

A flue is a duct, pipe, or opening in a chimney for conveying exhaust gases from a fireplace, furnace, water heater, boiler, or generator to the outdoors.


Flue Systems: The pipes that take fumes away from your stove and provide fresh air for the fuel to burn efficiently
Midtherm Flue Systems offer a complete range of stainless steel flue systems (including twin wall and Coloured Vitreous Enamel) for all kinds of appliance from wood burning stoves to large commercial boilers.
A flue system can be constructed using a series of pipes and components to convey the gases from the appliance or open fire to outdoors.
This means that whilst you can install an appliance and connect the flue into your existing masonry chimney, you can also build a chimney from flue pipes without the need for connecting to a masonry chimney.


Why do I need a flue system?
If you wish to install an appliance i.e. wood burning stove, in your property and do not have an existing masonry chimney then a flue system can be constructed, either through the property and exiting through the roof, or through the wall to rise externally.
If there is a masonry chimney/existing chimney in the property, it is still good practise to line the chimney when installing an appliance. This is because a flue system improves the efficiency of the appliance by creating an efficient draw by allowing an adequate air supply.
To satisfy the requirements of: building regulations Document J as listed on page 9


Chimney Lining
Most stove installations (within a chimney) will involve the use of a lining which can improve the draw of the chimney; reduce both condensation in the flue system, and the risk of a chimney fire.
Due to the efficiency of stove and uses of secondary combustion much of the energy from your fuel is used to heat the stove and surrounding air. This causes the heat of the extracted gases to be generally cooler than that of a normal open fireplace. Cooler gases can result in tar deposits if in contact with condensation with the flue system. Build-up of tar can increase the risk of a chimney fire as it sticks to the sides of the chimney.
Lining the chimney insulates the flue system reducing the condensation present reducing tar deposits. This can be further improved upon by insulating the liner with Rockwool sleeves or chimney wrap through-out the length of the liner. The liner is and made from steel which tar does not easily stick to which also reduces the possibility of chimney fires.
It is therefore good practise to install a liner when installing a wood burning appliance.


Key Reasons for use of appropriate flue liners:

  • Stop the products of combustion from corroding brick chimney
  • Reducing the possibility of and containing chimney fires
  • Enabling efficient maintenance of a chimney
  • Insulated flue improves the efficiency of the appliance

Stainless Steel Flue Systems

Where there is no existing chimney then twin walled stainless steel flue system is required. The pipes on a wood-burning stove get extremely hot and twin wall (i.e. double-Insulated pipes) protect the ceiling; walls and roof from the heat transferring through the pipes and creating a potential fire hazard.

Twin wall systems are used for both interior and exterior flue systems and are also suitable for multi-fuel appliances. These are more complex systems and subject to building control regulations, therefore we would always recommend that a professional HETAS registered installer is used to fit the stove and flue system.

The flue systems can usually be designed by the fitter to suit the property and setting of the stove; including incorporating safety features; cleaning and access support within the design.

What flue system is required?
The right flue system ensures your appliance is safe and reliable as well as efficient, ultimately creating the right draw of air to ensure all gases are taken up the flue system
It is important to select a flue system suitable to your stove and chimney in order to achieve the best results. Not all chimneys draw effectively enough to enable your stove to burn fuel and extract gases properly and all stove installations now come under building control which is why using a HETAS registered installer is recommended. (HETAS are the governing body for this sector).

Simple Chimney Installation
Prior to installation of a stove it is recommended the chimney is swept and inspected by a NACS approved chimney sweep, who can also perform a smoke test to assess the draw of the chimney and identify any leaks or defects which would need to be addressed.
In situations where it is possible to connect the flue from the stove straight into the chimney a vitreous enamel flue pipe is generally used which connects directly to the stove and into the chimney. The chimney is then blocked off with a register plate to enable the draw to remove air through the stove.






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