INSTALLER’S GUIDE
Page 9
2.9.4
Metal Flue Box
A twin wall metal flue box conforming to BS715 with a minimum internal depth of
200mm. Incombustible mineral wool insulation of not less than 50mm thickness must be
applied to the top surface of the firebox and it must stand on a non-combustible hearth.
There must be an air gap clearance of 50mm all round the outside of the box and above
the top insulation to any combustible material.
The opening must be within the following dimensions:
Width
Max.
432mm
Min.
407mm
Height
Max.
610mm
★
Min.
560mm**
★
Though the total height of the closure plate will accommodate a maximum opening
height of 650mm, heights above 610mm will leave the closure plate and sealing tape
visible above the appliance.
**This fire has been tested for use on the “Rite-Vent” 7T95125 metal flue box and found
to be satisfactory.
2.10
If the fireplace opening is greater than the acceptable dimensions given in this
guide, do not use the back of a fire surround or marble to reduce the opening. This
may cause cracking of the surround back or marble
.
2.11
The following flues are suitable:
•
225mm x 225mm conventional brick flue.
If a flue liner is used, it must be a minimum of 125mm diameter. The liner must be sealed
to the surrounding area above the fireplace opening and to the top of the chimney. An
approved terminal must be fitted.
•
A properly constructed precast flue conforming to B.S 1289.
•
A flue pipe with a minimum diameter of 127mm. See B.S 6461 Part 1 for suitable
materials. Metal flue pipes must comply with B.S 715. See section 2.9.4 of this guide for
flue box opening sizes.
2.11.1
The flue must conform to BS 5440: Part 1 in design and installation.
The flue, measured from the bottom of the fireplace opening to the bottom of the
terminal, shall be not less than 3m in actual vertical height. When calculated in
accordance with BS 5440: Part 1 Annex A, the minimum
equivalent
height of the flue
shall be 2.0m of 125mm dia. flue pipe.
2.11.2
The flue must be clear of any obstruction and its base must be clear of debris.
2.11.3
The flue must be completely sealed so that combustion products do not come into
contact with combustible materials outside the chimney.
2.11.4
The flue must serve only one fireplace.
