The ventilation slide rule is an easy-to-use pocket guide that reflects the general requirements of British Standard 5440-2 "Installation and maintenance of flues and ventilation for gas appliances of rated input not exceeding 70kW net (1st, 2nd and 3rd family gases)" – Part 2: "Specification for installation and maintenance of ventilation for gas appliances." As well as providing essential technical advice, the pocket guide has 2 slide rules, one for open-flued appliances and one for room-sealed appliances, which when combined with the heat input of the appliance, gives quick and accurate information on the ventilation provision both for combustion and compartment cooling (if required).