The instructions supplied with French models carry information relating to installing as a heat exchange unit, this is not normal procedure in the UK.
We have standard chimneys as opposite.
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The advantage of the French system is that the warm air created by the body of the unit is circulated through vents from within an enclosed cavity, or, piped through to other rooms.
The disadvantage is that you would have to remove your fire breast and construct a new one to accommodate the cavity required. On a safety note, this system leaves itself open to releasing life threatening fumes into rooms should the chimney flue become ruptured. There are flue systems available and a Corgi gas installation accredited company would be the best choice for advice.
The drawing above gives you the simple information of how it sits in an opening. The flue is attached and the fireplace surround built to the required size. There is no specific gap required around the unit when used with a standard chimney situation. If you wish to have the facility of removing the unit in the future then it is suggested you make the opening higher. Put the unit in and connect your pipe and then lift it up placing bricks or similar underneath the base. The space underneath the unit at the front must then be covered with a removable plate or bricks to allow you to 'drop' the unit down to remove it. There is no plate sold to do this, it is simply something to consider when you are designing the surround.
For future sweeping, the metal plate that sits in the inside top of the fire can be removed to allow access to the flue.
