Step-by-step chimney flow check and spillage observation methods.
To verify that an open-flued appliance can discharge its combustion products safely, two distinct flue testing procedures are carried out under BS 5440-1:
- Flue Flow Test (Chimney Check): This is a mechanical integrity check of the chimney before the appliance is lit. A smoke match or smoke pellet is placed in the flue opening or draught diverter slot. The smoke must be observed for at least 15 seconds to ensure it is drawn continuously and cleanly up the chimney without spilling back into the room.
- Spillage Test: This is carried out after the appliance is commissioned and lit. The appliance is operated at its maximum heat input for 5 minutes (to allow the chimney to warm through and establish a stable thermal updraft). A smoke match is then passed along the edge of the draught diverter or canopy. Any smoke blown back into the room indicates spillage (flue products escaping), which is Immediately Dangerous (ID).
*Original revision guidance; verify testing durations and safety classifications against BS 5440-1 and the GIUSP.*