Vent Size

Ventilation of Domestic Natural Gas Appliances
These notes are for information only and should not be used as a substitute for
normative documents or manufacturer’s instructions. The notes have been carefully
checked for errors but RAD Training (Midland) Ltd. accepts no responsibility for any
consequences ensuing upon their use or reliance upon information within them.
These notes form part of the domestic ACS natural gas training programme from RAD
Training Midlands. They cover the underpinning knowledge requirements for the
ventilation of domestic natural gas appliances. An up-to-date version of these notes is
available from www.radmidlands.co.uk

Contents
Page
2

Topic
Why is ventilation important?
Normative documents
Determining the category of unsafe situation

3
4

Types of gas appliance
Flueless appliances
Open flue appliances
Room sealed appliances

5
6

Ventilation of flueless appliances
Examples

7

Ventilation of open flue appliances
Adventitious air
Decorative fuel effect (DFE) appliances
Examples

8
9

Ventilation of rooms containing more than one appliance
Examples

11

Provision of ventilation

13
14

Appliances in compartments
Examples

16

Ventilation taken through adjoining rooms
Example

17

Heat input, net and gross
Conversion table for common units of power and gas rate

18

Glossary

Ventilation of Domestic Natural Gas Appliances

© RAD Training Midland 20/01/2011

Page 1 of 18

Why is ventilation important?
Gas needs a certain amount of oxygen to burn correctly. One cubic metre of gas needs
ten cubic metres of air for complete combustion.
The most serious effect of under-ventilation is incomplete combustion. This is where
lack of oxygen causes carbon monoxide (CO) to be produced. CO is an extremely
poisonous gas.
Some gas appliances take their combustion air from the room, which must then have a
permanent source of fresh air. It is crucial that air vents are...