CENWAT Flue Requirements & Pressure Relief 4

Question 1

What is a balanced flue boiler?

Accepted Answer

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

Answer

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.

Question 2

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

Accepted Answer

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

Answer

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.

Question 3

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

Accepted Answer

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

Answer

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.

Question 4

What is a flue liner and when is it required?

Accepted Answer

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

Answer

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.

Question 5

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

Accepted Answer

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

Answer

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.

ACS CENWAT Practice Test

ACS CENWAT Practice Test

CENWAT Flue Requirements & Pressure Relief 4