HETAS registered installer since 2013
GTD logo

HETAS Installer based in Hitchin, Hertfordshire

Installing Woodburners in Herts, Beds & Bucks

01462 431910

GTD Installations Ltd

Building Regulations

Changes to the building regulations were introduced in 2010. Before this a wood burning or multifuel stove could be installed using only the existing masonry chimney to remove the potentially dangerous fumes from the stove. All stoves installed after 2010 must meet very specific conditions to be considered safe. If your stove was installed before this, there is a good possibility that needs a liner fitting. For more info visit HETAS

There should also be a hearth, CO detector, register plate and cowl to stop animals from entering your flue / chimney and creating harmful blockages. Your installer should leave you with a HETAS certificate and data plate.

Flexible liner and twin wall systems can degrade over time and will need regular sweeping to prolong their life. This is best done at the beginning of Summer.

Building Regulations -  Part J

"We really felt at ease through the whole process and would definitely recommend you"  - Jonathan in Beds

Flexible Liner

Stainless Steel Liner

To be a legal installation a connection needs to be made from the woodburning stove to the top of the chimney. If you do not have a clay or pumice lined chimney, as many new builds do, you may be advised to use flexible liner. 

316/316 Flexible Liner

Flexible liner made of 316 grade steel is used to line the chimney connecting the cowl on the chimney pot, to the vitreous pipe exiting the woodburning or multifuel stove, via the chimney flue. Suitable for wood, gas, and oil it has around a 15 year life expectancy when used with these fuels. HETAS approved product.

904/904 Flexible Liner

904 grade steel liner is thicker than 316 and is also used to connect the cowl to the enamelled pipe on the stove. As it is more robust it is suitable for wood, gas, oil & smokeless fuel. It comes with a 35 year product replacement guarantee and is a HETAS approved product.

Building Regs insist that install is accessible by your chimney sweep

Protect your flooring

Another requirement of the regulations is the hearth area, which is the area underneath the stove and directly in front of it, shown here by the black and white tiles.


These regulations have recently been reduced and state that the hearth should extend a minimum of 225mm in front of the stove. However, we feel that this is a little small and we recommend 300mm in front of the stove in order to protect your flooring or carpet from being damaged by any burning debris that occasionally may escape from the fire when you are loading it.


We recommend 20mm or 30mm honed granite as it is very durable but other suitable materials are slate, gass, marble, stone, tiles and precast concrete. We will measure for your new hearth and have the Stonemason cut it to size ready for fitting, usually a week later.

"they work so hard to make it right and it looks beautiful, very happy" - Julie in Cottered

Contact us for repairs
Suspending Cowl

Stop unexpected guests

A cowling is also required as this will stop birds and squirells from sheltering in your warm chimney and setting up home. A nest in your chimney will cause harmful gases to escape into your house and may even set alight and cause a chimney fire. There are many different types of cowl on the market.


A suspending cowl (also known as a pot hanging cowl) is attached to the chimney pot and holds the liner in place.It will protect the opening from the weather and also from birds as it is surrounded by steel mesh. As stainless steel lasts for years longer than cheaper materials; we only supply cowls made of 316 Stainless Steel from HETAS approved suppliers.

DEFRA approved wood burners
Multi-fuel freestanding stoves

"I would have no hesitation in contacting you again" - Alan in Letchworth

Access Hatch

Aid Chimney Sweeping

Another requirement of the 2010 regulations was to ensure that when a stove is installed that adequate access is provided to sweep the chimney in the future. Older installations may not allow for this which makes it very difficult for the chimney to be cleaned and your chimney sweep may refuse to do it and indeed condemn your installation.

You would usually find an access hatch in the section of black vitreous pipe that directly connects to your stove and enters the chimney. They are mainly used on stoves without a removable throat plate or baffle plate on the inside of the stove, such as Gas woodburner effect stoves.

Most stoves have a removable throat plate as this ensures good cleaning from the tip of flue to the bottom of the stove.

Throat Plate

Air control

You will find the throat plate inside the stove at the top. It is made of metal  and is a very important part of the stove. Also known as the baffle plate it is what makes your woodburner more efficient by slowing down the release of heat up the chimney.

It should never be removed, unless by a chimney sweep when cleaning the chimney. If yours comes away or falls easily, have your sweep check the bolts that hold it in place for signs of wear and tear.


Occasionally throat plates become damaged and need replacing. They can usually be purchased direct from the manufacturer of the stove and you should check your warranty before ordering as it will be covered if still under guarantee. If your stove is no longer in production you could have one especially fabricated, which is cheaper than buying a new stove!

Need your flue lining?
More questions about building regs?
Other items

Data Plate

Your installer should complete one of these and leave in an accessible place such as the Electicity Supply cupboard. It holds data useful for the fire service.

Register Plate

This blocks of your chimney above your fireplace allowing the enamelled pipe to go through. This will stop debris such as pargin which older chimneys were lined with and mortar from falling into your living space. It will also hold any insulation up if required.


You may find that by insulating the area between the flue lining and the brick chimney wall that you make the most of the heat produced by your woodburning stove. Rockwool lengths can also be used for the same purpose. Useful for chimneys on cold exterior walls and thatched cottages. The fire bricks inside your stove are also made of this heat resistant material. Contact us if you need to replace your fire bricks.


Building Regulations Part J
Stainless steel chimney liner creates a physical connection from the stove to the top of the chimney, as required by Building Regulations Part J
Tiled hearth area must be at least 225mm in front of the stove. Larger is better if possible.
Suspending cowl on a chimney to stop vermin entering
An access hatch is a door on a pipe which allows the sweep to clean your flue annually as required by Building Regulations Part J
Visit GR8 fires to buy a throat plate. Photo copyright GR8fires.co.uk
Data Plate
Flexible chimney liner in chimney before chimney was rebuilt

""thank you for all your help, the new fire place looks amazing" - Steven in Potton

Twin-Wall System

Don't have a fireplace?

If you don't have an existing chimney stack then you will be advised to use a twin-wall system. This will be designed specifcally for your property and is made up of lengths of double-walled pipe with insulation between them. The system will need to include a cowl, hearth, data plate and hearth to be HETAS certified. It will connect to the stove and exit the fumes 4.5 metres above as required by Building Regulations Part J.

Quality Stainless Steel

There are many different twin wall manufacturers and systems. We always use a stainless steel system over the cheaper galvanised steel as research has shown it to be more durable at high temperatures and less susceptible to corrosion and rust. It is available in silver or black.

Building Regulations requires your flue to be 4.5m tall.
Twin wall / rigid pipe system for fires without a chimney stack or fireplace