fireplace/fire will fit your required application.
dimension you need to work out is the depth needed to fully recess you
fire against your flat wall or in your chimney recess. If the fireplace
is being fitted against a flat wall then the full depth of the fire
needs to be recessed within the fire surround. However, if the fire
surround is being fitted against a chimney then the depth of the fire
can be recessed within the cavity of the chimney.
The rebate is the distance from the back of the wall to the front of
the back panel. Deeper rebates allow the back panel to be brought
forward, creating a void between the panel and the wall. Deep rebates
are popular where inset electric fires, or flueless gas fires are to be
installed onto flat walls.
To work out the fire recess, you subtract the rebate by 20mm to
accommodate the thickness of the panel. Therefore 100mm rebate gives you
80mm fire recess depth (100mm - 20mm for the back panel).