Every Home is unique, with its own heating and ventilation requirements. The information below will help you decide the correct choice for yours.
Chimney (Usually Class 1)A traditional brick or stone built stack with accompanying terracotta pot or gas terminal. Internal dimensions are usually 9" x 9" (230mm x 230mm) square or 7" (178mm) diameter but sometimes a little smaller or larger depending on the construction. Sometimes these traditional types of flue are lined with a flexible stainless steel liner or a refractory lining of some kind, especially if they are old and damaged or unsound in some way. The liner may commonly be 5" (127mm) or 7" (178mm) inside diameter and must be twin wall for solid fuel although single wall type is OK for gas fires. A metal lined flue is often a class 2 type flue. It must be a single continuous length and sealed to the inside of the flue or fireplace top and bottom and/or directly connected to the appliance at the bottom where necessary.
Pre-Fabricated (Usually Class 2)Consisting of a metal flue box and tubular flue system protruding out of the roof with a gas terminal or cowl on the top. In the UK it may commonly be 5" (127mm) or 7" (178mm) inside diameter and should be double (twin) wall construction of at least gas fire quality (solid fuel quality is even better). Often built into a boxed off section of rooms that it passes through. It should be installed with proper clearances to combustible materials and proper firestop spacers etc between floors. The firebox at the bottom for installing the fire into may be of various sizes so do check dimensions before ordering your fire. The firebox will usually be built into some kind of false chimney breast or feature to conceal it.
Pre-CastBuilt into an internal wall from proper refractory concrete blocks and usually identified by a ridge vent or metal flue tube and terminal. Only suitable for gas fires which are designed to work on pre-cast flues. Often there is no sign of the flue inside the house as they are flush with the wall, but a twin wall flue section from the wall connection adaptor to the ridge vent is often present in the loft space. Pay attention to the condition of this type of flue, particularly joints to the terminal and twin wall flue section in the loft and mortar fangs and debris/cobwebs building up inside the flue which can cause appliance safety and performance hazards. Other potential difficulties can arise from pre-cast flue blocks that are directly plastered as the proper construction method is in fact battenning or dabs to space the plasterboard off the hot surface of the flue. Wall temperatures of this type are not appliance related,they are always wall construction related.
No FlueIf you have nothing on your roof you probably have no chimney or flue and will require a balanced flue or fanned flue fire that will fit on a suitable outside wall. Fireplacenet supply both of this type of fire.