CCN1 Combustion and Ventilation 2

Question 1

When testing the combustion performance of a gas appliance, what does a high CO/CO₂ ratio indicate?

Accepted Answer

Incomplete combustion is occurring

Answer

A high CO/CO₂ ratio indicates incomplete combustion. The acceptable maximum CO/CO₂ ratio for most appliances is 0.004 (or 1:250). A ratio exceeding this indicates that the appliance is producing dangerous levels of carbon monoxide relative to the carbon dioxide output, and the appliance requires investigation and rectification.

Question 2

What is 'vitiation' in the context of gas appliance operation?

Accepted Answer

The progressive reduction of oxygen in a room due to an appliance consuming air for combustion

Answer

Vitiation occurs when an open-flued or flueless appliance consumes oxygen from the room for combustion, progressively reducing the oxygen level in the space. This can lead to incomplete combustion, increased carbon monoxide production, and ultimately a dangerous situation if adequate ventilation is not provided.

Question 3

What is the minimum free area of a permanent air vent required for a flueless gas appliance such as a cooker with a rated input of 15 kW?

Accepted Answer

5 cm² per kW of rated net input

Answer

Flueless appliances require ventilation of 5 cm² of free area per kW of rated net input for the total input of the appliance (not just the amount above 7 kW as with open-flued appliances). For a 15 kW flueless appliance, this would require 75 cm² of free area ventilation.

Question 4

What colour flame indicates correct combustion on a natural gas burner?

Accepted Answer

Predominantly blue with a clearly defined inner cone

Answer

A correctly adjusted natural gas burner should produce a predominantly blue flame with a clearly defined inner cone (primary combustion zone). Yellow or orange flames indicate incomplete combustion due to insufficient primary air, while a lifting or floating flame suggests too much primary air.

Question 5

What happens to the products of combustion from a decorative fuel effect (DFE) gas fire?

Accepted Answer

They are discharged through a conventional chimney or flue

Answer

A decorative fuel effect (DFE) gas fire is an open-flued appliance that discharges its products of combustion into a chimney or flue. Although the fire may appear similar to a flueless appliance, it relies entirely on the chimney or flue for safe evacuation of combustion products. The flue must be tested for safe operation.

ACS CCN1 Practice Test

ACS CCN1 Practice Test

CCN1 Combustion and Ventilation 2