Travis Industries DVL Insert EF II Owner's Manual page 8

Min. 23-3/4"
The gas line and shutoff
valve should be installed
prior to insert placement.
For tight fits (under 28"), see the section "Removing the Vent Connector"
Min. 31-1/2" - additional space may be required for gas line installation.
Attach the "This fireplace has been altered..." plate
to the fireplace (use two screws or other suitable
method). You may wish to place it in a location
where it will be covered by the surround panels.
The DVL inserts 14-1/2" into the
fireplace.
See "Leveling Bolts" for details
on leveling the heater.