We have recently had a gas back boiler and open flame fire front removed. We plan to get a hole in the wall high efficiency glass fronted gas fire fitted with a 4.2 kW output. We have a largish vent in the room courtesy of the last installation. This vent sits behind a radiator. Once the fire is delivered, the gas fitter will be round to look at the job again, but is he likely to suggest that we keep the current vent, as it is already there. The reason I ask is that we want cavity wall insulation and the vent is not sleeved so we will have to fit a new sleeved vent to the existing hole at least. I am just trying to plan ahead a bit. The room has been stripped back to brick so want to plan all such work now.