I currently have an open fireplace with chimney (which is open and has been swept) in which the previous owner installed a gas type fire which is run off a gas bottle outside. I'm unsure of the KW of this fire.

Before the installers would do the cavity wall insulation they said this must not be used again because of the free air flow? I'm not 100% sure what they mean by this as I was under the impression any fire under 5KW did not need this air vent. Is it just so there is always a supply of air entering the room incase there was a gas leak/carbon monoxide?

Could anyone with a knowledge of this actually explain it?