DM System Chimney Internal – Video and FAQ


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What size of flue for an open fire?

It is recommended to use one of our firechests which will predetermine the flue size. For further details kindly contact our Technical department to size your flue requirement.

What size of flue is required for my appliance?

The flue size is dictated by the appliance manufacturer. The pumice flue must not be less than the spigot diameter of the appliance.

Which way up does my flue liner need to go?

The flue liner must be placed socket upwards.

Can I use ordinary mortar to bed the flue components?

No, you must use our lip glue adhesive. The instructions for mixing are on the packet.

Do I need a bend?

It is recommended that chimneys should be built straight wherever possible. In the scenario that in can’t, then we can provide a range of bends with different angles.

What is the minimum flue height?

For an open fire you require a minimum height of 4.5m from top of opening.

Additionally, 4.5 m from the top of appliance but please refer to manufacturer’s instructions.

What is the minimum thickness for leca insulations?

The minimum thickness of leca you require between a pumice liner and masonry chimney is 15mm.

Do I need a chimney pot or terminal?

It is not essential for you to have a chimney pot or terminal, although it can be used for aesthetic reasons or to help prevent rain or birds entering the flue.

Do I need an air brick?

Yes, combustion air is required for natural draft chimneys. The amount required will depend on the size of open fire or chosen appliance. Please follow Document J of the building regulations guidelines.

Do I need to line the pumice with stainless steel?

No, but is important to get the correct diameter of pumice flue to match your appliance.

What distance do I need to combustible material?

The distance to combustibles is 38mm from the outside of the DM chimney system and is 40mm from the outside of a masonry chimney when using pumice liners.

What fuel can I burn?

You must use dry season wood with less the 20% moisture content or HETAS approved solid fuels, gas or oil.

Can I use pumice for my condensing appliance?

Pumice is only suitable for dry chimney situations, therefore cannot be used for condensing appliances, including pellet and biomass.

Do I need a soot door?

If an appliance flue pipe connects into the side of a chimney you must have soot door below the flue pipe entry. If the chimney is built above the appliance you can sweep through the appliance or connecting flue pipe.

How often do I need to sweep my chimney?

It is recommended to sweep your chimney twice a year , once at the start of the heating season and once at the end . You may also need to sweep during the heating season depending upon use.


Connection to an appliance, which is not connected to the fuel supply, may be carried out by a competent person. However, connection to an appliance, which is connected to the fuel supply, must be carried out by a GAS SAFE (gas) or OFTEC (oil) registered installer.

Schiedel Chimney Systems Ltd. recommends the use of HETAS registered installers for solid fuel applications.

This installation assistant is to be used as a visual aide only, by qualified installers, in conjunction with the detailed component installation instructions. For full design and installation details, the key referral documents are as follows:-

  • BS EN 13229: Inset appliances including open fires fired by solid fuels. Requirements and test methods.
  • BS EN 1858: Chimneys. Components. Concrete flue blocks.
  • BS EN 1443: Chimneys – General Requirements
  • BS EN 15287-1: Chimneys. Design, installation and commissioning of Chimneys for non-roomsealed heating appliances.
  • BS EN 5440-1: Flueing and ventilation for gas appliances of rated input not exceeding 70kW net (1st, 2nd and 3rd family gases). Specification for installation of gas appliances to chimneys and for maintenance of chimneys.
  • Approved Document J: Combustion appliances and fuel storage systems (England and Wales)
  • DFP Technical Booklet L:- Combustion appliances and fuel storage systems (Northern Ireland)
  • Technical Handbook (Domestic & Non Domestic), Section 3 – Environment (Scotland)
  • Appliance Installation Instructions and related standards. Other standards covering specific applications will also be relevant and should be adhered to.

Planning permission may be required and reference should be made to the local Building Control Department.

Ensure all chimney components are available and check them to ensure there has been no damage.

Do not use damaged components. Build the chimney up to follow the previously designed route, which should be as straight as possible.