Gas fire wall/floor vent requirements?

I have a gas fire installed ~2yrs ago in a room ~3mX3m Does anyone know what are the wall/floor vent requirements if any? The fire is fed into a chimney. There were originally 2 vents in the room (one in the floor and one in the wall) which were installed years ago, well before recent gas fire. However, during recent building work the builders have covered over both. Any sugestions on what the requirements are? Cheers