CCN1 Flue Systems and Chimneys 2

Question 1

What is the minimum distance a balanced flue terminal must be from an opening window, air vent, or other opening into a building?

Accepted Answer

300 mm

Answer

A balanced flue terminal must be positioned at least 300 mm from any opening into a building, including openable windows, air vents, and doorways. This separation prevents combustion products from being drawn back into the building. Specific distances may vary depending on the appliance rating and flue type — always refer to the manufacturer's instructions and BS 5440-1.

Question 2

What material is commonly used for flexible flue liners in gas installations within masonry chimneys?

Accepted Answer

316 grade stainless steel

Answer

316 grade stainless steel is the standard material for flexible flue liners used in gas installations within masonry chimneys. It provides excellent resistance to the corrosive condensates produced by gas combustion and has the durability required for the expected lifespan of the installation. It must conform to BS EN 1856-2.

Question 3

When installing a vertical flue from a gas boiler through a flat roof, what is the minimum height the flue terminal must extend above the roof surface?

Accepted Answer

600 mm

Answer

A vertical flue terminal passing through a flat roof must extend at least 600 mm above the roof surface. This height ensures adequate dispersal of combustion products, prevents the terminal from being blocked by debris or ponding water, and reduces the risk of flue gases being drawn back into the building through nearby openings.

Question 4

What is the purpose of a flue gas analysis test carried out during commissioning of a gas boiler?

Accepted Answer

To measure the carbon monoxide, carbon dioxide, and flue gas temperature to verify safe and efficient combustion

Answer

A flue gas analysis (FGA) measures the levels of CO, CO₂, O₂, and flue gas temperature in the products of combustion. This verifies that the appliance is burning efficiently and safely, with combustion products within acceptable limits. The CO/CO₂ ratio must be within safe limits (maximum 0.004 for most boilers).

Question 5

When a chimney serves an open-flued gas fire, what test must be carried out to confirm the chimney is safe to use?

Accepted Answer

A smoke test (flue integrity test) and spillage test

Answer

Before connecting an open-flued gas fire to a chimney, a smoke test (flue integrity test) must be carried out to confirm the chimney is structurally sound and does not leak combustion products. A spillage test must also be performed with the appliance operating to ensure the chimney provides adequate draught and products of combustion are safely evacuated.

ACS CCN1 Practice Test

ACS CCN1 Practice Test

CCN1 Flue Systems and Chimneys 2