Combustion & Flues Flashcards
6 cards from real ACS practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Combustion & Flues flashcards as text
What is the minimum distance that a flue terminal must be positioned above an openable window or door, as required by BS 5440 Part 1?
Answer: 300mm
BS 5440 Part 1 specifies minimum separation distances between flue terminals and openings such as windows and doors to prevent flue gases being drawn back into the building — typically 300mm minimum.
What causes 'sooting' of a gas appliance heat exchanger or burner?
Answer: Incomplete combustion due to insufficient air, a blocked burner, or a restricted flue, producing soot (carbon) deposits instead of clean combustion products
Sooting is a symptom of incomplete combustion — insufficient oxygen or a faulty burner prevents complete conversion of carbon to CO2, depositing carbon as soot and almost certainly producing CO.
What is a 'plume management kit' used for on a condensing boiler?
Answer: To direct the visible water vapour plume from the flue terminal away from windows, doors, and neighbouring properties
A plume management kit redirects the highly visible water vapour plume produced by a condensing boiler flue terminal, preventing it from obscuring windows or causing nuisance to neighbours.
What does 'excess air' mean in combustion analysis?
Answer: The amount of air supplied above the stoichiometric (theoretical) minimum needed for complete combustion, measured as a percentage above the theoretical requirement
Excess air is the additional air beyond the stoichiometric minimum required to ensure complete combustion; some excess is needed to ensure complete burning, but too much reduces efficiency by carrying away heat.
Which condition in a flue system can cause 'backdraught' and allow combustion gases to enter a room?
Answer: Negative pressure in the building from extract fans, trickle vents, or sealed rooms that reverses the natural draught in the flue of an open-flued appliance
Modern buildings are often very airtight; powerful extract fans or extractor hoods can create negative internal pressure that reverses the draught in an open flue, causing combustion gases including CO to spill into the room.
What is the 'stoichiometric air-to-fuel ratio' for natural gas combustion?
Answer: Approximately 10:1 (air:fuel) by volume — approximately 10 cubic metres of air are needed to completely combust 1 cubic metre of natural gas
Methane requires approximately 10 volumes of air (roughly 2 volumes of oxygen with 8 volumes of nitrogen) for complete combustion — insufficient air causes incomplete combustion and CO production.