Gas Safe ACS - Accredited Certification Scheme Ventilation Requirements Questions and Answers

Question 1

An open-flued gas boiler with a net heat input of 22 kW is to be installed in a room. According to BS 5440-2, what is the minimum required free area for a single purpose-provided air vent communicating directly with the outside air?

Accepted Answer

75 cm²

Answer

BS 5440-2 specifies that for an open-flued appliance installed in a room, an allowance is made for adventitious (unplanned) ventilation equivalent to the first 7 kW of heat input. For any input above 7 kW, purpose-provided ventilation of 5 cm² per kW is required. The calculation is: (22 kW - 7 kW) x 5 cm²/kW = 15 kW x 5 cm²/kW = 75 cm².

Question 2

You are installing a flueless gas cooker with a total net heat input of 9 kW in a kitchen with a volume of 8 m³. According to BS 5440-2, what are the ventilation requirements for this installation?

Accepted Answer

A permanent air vent with a free area of 50 cm² is required.

Answer

For a flueless domestic cooker installed in a room with a volume between 5 m³ and 10 m³, BS 5440-2 requires a permanent air vent with a minimum free area of 50 cm². If the room volume were less than 5 m³, a 100 cm² vent would be needed. If it were over 10 m³, no permanent vent would be required, assuming an openable window is present for rapid ventilation.

Question 3

Which of the following statements regarding 'adventitious ventilation' in the context of gas appliance installation is correct?

Accepted Answer

It is the uncontrollable airflow through cracks and gaps in the building fabric.

Answer

Adventitious ventilation refers to the natural, uncontrolled air leakage into a building through gaps around doors, windows, and other parts of the building structure. For certain open-flued appliances, BS 5440-2 allows this to provide the first 7 kW of combustion air requirement, but its presence should not be taken for granted in modern, well-sealed properties.

Question 4

A gas appliance is to be installed in a purpose-built compartment. The ventilation for the compartment will be provided directly from the outside. According to BS 5440-2, what is the ventilation requirement for the low-level air vent?

Accepted Answer

10 cm² per kW of total net heat input.

Answer

When a gas appliance is in a compartment ventilated directly to the outside, BS 5440-2 requires both high and low-level vents. The high-level vent requires 5 cm² per kW, and the low-level vent requires 10 cm² per kW of the appliance's total net heat input.

Question 5

Under what circumstances may an existing air vent that communicates with a roof space be considered acceptable for a gas appliance under the updated BS 5440-2:2023?

Accepted Answer

If it is an existing installation, the total free area is satisfactory, and the opening is free from obstruction.

Answer

The updated BS 5440-2:2023 states that any *new* air vent shall not communicate with a roof space. However, it allows for *existing* air vents communicating with a roof space to remain acceptable, provided the engineer verifies that the total free area is sufficient for the appliance and that the vent opening is clear of any obstructions like insulation.

Gas Safe ACS Practice Test

Gas Safe ACS Practice Test

Gas Safe ACS - Accredited Certification Scheme Ventilation Requirements Questions and Answers