A Gas Ventilation calculator for working out ventilation requirements for gas appliances. Open flued, Room sealed, Flueless appliances. This gives you the option of working out ventilation when more than one appliance is fitted in a room. For existing and new ventilators you can calculate the free air area of the vent to work out if its suitable for the appliance(s) it is feeding. No more formulas and calculations to remember, read the heat input from the appliance data badge and press calculate.Check out the tutorial http://www.youtube.com/watch?v=zxmUMVTbneYif your having problems email: [email protected] downloaded the Licensing Service requires validation, this must be done via the phones CELLULAR DATA not through Wi-FI.