Flue Requirements & Pressure Relief Flashcards

What is a balanced flue boiler?

Answer: A room-sealed boiler where the flue terminal faces the outside, drawing in combustion air and expelling flue gases in a balanced arrangement

A balanced flue boiler is room-sealed with a concentric terminal positioned on an outside wall; air is drawn in through the outer annulus and flue gases expelled through the inner tube, with wind effects balanced on both.

What is a fan dilution flue system (also known as a 'Potterton Performa' type fan flue)?

Answer: A system where a fan dilutes flue gases with large amounts of air before discharge, allowing flexible terminal positions

Fan dilution systems use a high-volume dilution fan to mix large quantities of air with flue gases, reducing their temperature and concentration, which allows more flexible terminal siting.

What is the minimum flue gas temperature that a flue must be designed to withstand on a condensing boiler?

Answer: The condensing boiler flue must withstand flue gas temperatures specified by the manufacturer, typically up to 120°C

Condensing boiler flues operate at much lower temperatures than non-condensing boilers (typically 50–120°C) but must still be rated for the maximum temperature specified by the appliance manufacturer.

What is a flue liner and when is it required?

Answer: A flexible or rigid duct inserted into an existing chimney to provide a safe gas-tight flue passage

A flue liner is installed inside an existing chimney or flue duct to provide a correctly sized, gas-tight and heat-resistant passage for flue gases, required when using an existing chimney for a new appliance.

What is 'spillage' in the context of an open-flued gas appliance?

Answer: Flue gases spilling back into the room rather than being drawn up the flue

Spillage occurs when flue gases escape into the habitable space rather than discharging through the flue; it can be caused by blocked flues, down-draughts or insufficient ventilation.

What test is used to check for flue spillage on an open-flued gas appliance?

Answer: A smoke match or smoke pellet test near the draught diverter when the appliance is running

A smoke match or smoke pellet is held near the draught diverter while the appliance is at operating temperature; smoke should be drawn into the flue. If it spills into the room, a spillage problem is confirmed.