It depends if the gas fire is open fronted or glass fronted.
Open fronted gas fireplaces work in much the same way as a traditional open wood fireplace. This means the fire will use air from the room as an ignition source, and while a certain amount will be drawn under the fire and recirculated into the room, a proportion of the rooms warm air will be drawn into the fireplace box and travel out through the flue.
All Escea fireplaces are glass fronted sealed units. This means air is introduced directly into the firebox (or heat chamber) from outside and pulled down the flue. Air within the room is pulled in through the front of the fireplace surround and over a heat exchanger then circulated back via either a fan or duct system. The fumes are then exhausted back out through another flue, so there’s no potential for harmful fumes to get inside the home.
All Escea gas fires are sealed, glass fronted fireplaces because this is the only way to seal the combustion area of the fireplace.
Learn more about open fronted vs glass fronted fireplaces here.