Flue Categories

• A, B, C - flueless, open flues, room sealed
• 1st digit - denotes method of arranging discharge of combustion
  • 1 - with draught diverter
  • 2 - with out draught diverter
• 2nd digit - denotes flue draught method
  • 1 - natural draught
  • 2 - fan downstream of heat exchanger
  • 3 - fan upstream of heat exchanger
  • 4 - fan downstream of draught diverter

Flueless

• Category A
  
  

Open-flued Systems

• Category B
• Balanced Compartments
  • Self-closing and draught proof door
  • Switch fitted to the door that turns off the appliance if the door is opened
  • Door shall not open into a bathroom
  • If over 12.7kW shall not open into bedroom
  • 'Keep closed' notice on the door
  • No other ventilation into compartment
• 4 parts of an open flued appliance
  
  • Primary Flue
    • Part of the appliance
    • Creates the initial flue pull to clear the products of combustion
  • Draught Diverter
    • Diverts any down draught from the burner
    • Allows dilution of flue products
    • Breaks any excessive pull on the flue
    • Usually part of the appliance
  • Secondary Flue
    • Horizontal runs must be avoided
    • Bend minimum 45°
    • Keep internal where possible
    • Minimum 600mm vertical rise to the first bend
    • Cross sectional area of flue must be at least equal to that of the appliance
  • Terminal
    • Stop birds nesting or leaves entering the flue
    • Minimise down draught
    • Help the flue gases discharge
    • Terminals are not required for chimneys with a flue size greater than 170mm if no nesting will occur
• Vertex Flue
  • Air supply taken from the roof space
  • Draught Diverter min height is 300mm above the loft insulation
  • The flue above the Draught Diverter must run for 600mm before any bend

Room-sealed Flue Systems

• Category C
• Balanced (natural draught) flue
• Fan-assisted flues
  • negative pressure within the casing
  • positive pressure within the casing
• Termination options
  • Vertical room-sealed flue termination
    
  • SE/U Duct room-sealed flue termination
    
    • C2 and C4 appliances (room sealed) may be installed
    • All air inlets should be labelled
    • All appliances should be labelled that flue system is shared

Shared Flues

• Each appliance shall have:
  • draught diverter
  • flame failure device
  • atmospheric sensing device
  • flue must be the correct size
  • chimney must have access for inspection and maintenance
  • appliances labelled that they share a flue