When installing a wood burning stove it is important to make sure that your installation is in accordance with the law. That means complying with Document J of the building regulations.
If your woodburner is not going to be placed in a fireplace recess and has been tested to verify that it cannot cause the upper surface of the hearth to exceed 100C, it must stand wholly above a non-combustible board, sheet or tiles that are at least 12mm thick.
Otherwise it must be wholly above a constructional hearth that is made of a solid, non-combustible material and that is at least 125mm thick, including the thickness of any non-combustible floor and decorative surface. If the constructional hearth is on a combustible floor then it must be 250mm thick or 125mm thick with a 50mm air gap beneath it before the combustible material.
Your heart must extend a minimum of 150mm to each side of the stove and 300mm in front of it.
For a freestanding stove, the hearth must be 840mm by 840mm, unless the stove is installed in a fireplace recess.
Flue outlet height
Document J also dictates the height above your roof at which the flue should terminate. The distance between the top of the flue pipe to the nearest horizontal point on your roof should be at least 2300mm.
The exception is if the flue terminates within 600mm of the ridge, in which case the flue pipe should be at least 600mm above the ridge. If the flue terminates within 2300mm of an adjacent building, again it must run at least 600mm higher than the adjacent building.
And if the flue will terminate below or within 2300mm of an openable rooflight, dormer window or other opening, the flue must run at least 1000mm above the top of the opening.
There are separate regulations relating to combustible roofing materials, such as thatch and shingles, so dig into the document to check those if that applies to your property.
A stove with a heat output of up to 20kW that is DEFRA exempt in accordance with the Clean Air Act must have a clue that is at least 5 inches (125mm) in diameter. All other stoves up to 30kW must have a flue that is at least 6 inches (150mm) in diameter.
Flue pipe distance to combustibles
If you’re using a single wall, uninsulated flue pipe it must be a distance at least three times its diameter away from any combustible material. So, a 6-inch flue pipe should be at least 18 inches away from anything combustible.
If that isn’t possible or practical, you can use a heat shield between the flue and the combustible material. The flue must be at least 1.5 times its diameter away from the heat shield, which must extend at least 1.5 times the flue’s external diameter either side of the pipe. There must also be an air gap of at least 12mm between the heat shield and the combustible material.
Flexible flue liners can only be used within existing chimneys and not in new chimneys. The liner must be of a suitable grade for use with woodburners. It must be installed in a continuous length with no joints allowed within the chimney.
Boxing in twin wall flues
If your twin wall flue (or factory made metal chimneys, as the building regulations have it) passes through a cupboard, storage space or roof space, it must be boxed in to keep it away from combustible materials. The relevant distance should be given on the flue itself and the guard should not be placed any closer than the distance given.
Woodburners need good levels of ventilation in order to perform effectively and safely remove gases from the stove, up the flue and prevent them seeping back into the room. Given the potential dangers of gases and smoke not being evacuated correctly, the levels of ventilation required are included in building regulations. The requirements are as follows:
Stove with a draught stabiliser fitted
Air permeability > 5.0m³/h.m²
300mm² for each kW up to 5kW
850mm² for each additional kW
Air permeability ≤ 5.0m³/h.m²
850mm² for each kW
Stove with no draught stabiliser fitted
Air permeability > 5.0m³/h.m²
550mm² for each kW above 5kW
Air permeability ≤ 5.0m³/h.m²
550mm² for each kW
Most homes other than those built very recently will have air permeability of more than 5.0m³/h.m², which means that no additional ventilation will be required in order to comply with the building regulations. You might choose to add more ventilation if the existing air supply is not resulting in an efficient burn and the safe evacuation of smoke and flue gases. Properties where the flue outlet is exposed to the wind are particularly prone to needing extra help.
If an additional vent is necessary, it can be place in the walls or floor of the room. It is advisable to place the vent near to the stove to reduce any draught in the room when the air is drawn into the appliance. Any protective mesh used over the outside of the vent must not have an aperture smaller than 5mm.
Some stoves are now available with an external air supply, which connects an outside air source directly to the appliance. This is a useful way of providing ventilation to the stove without compromising the airtightness or energy efficiency of your home.
You must notify your local authority’s building control department before installation work starts. The exception to this rule is if you are using an installer who is registered with a competent person scheme.
Carbon monoxide alarm
Carbon monoxide alarms are compulsory with all new wood-burning stove installations. This has been the case with all installations since 2010.
All woodburner installations are required to be accompanied by a notice plate, which should contain information that is essential to the correct application and use of the stove. The notice plate must detail the location of the hearth, fireplace or flue box to which it refers; the category of flue and generic types of appliances that can be safely used with it; the type and size of the flue (or its liner if one is used) and the manufacturer’s name; and the installation date.