We are remodelling our master bedroom and considering putting in a
vented gas fireplace opposite our bed.

However, we are tight on room so we need to know what is the minimal
depth that would be needed to add such a unit including space for
venting, fireplace itself, insulation, etc.

Of course, details will depend on the unit itself, but I would like to
get a ballpark estimate of the minimum space that would be needed so I
know whether it is even worth pursuing.

I tried googling some units but it wasn't clear in practice how much
total space is required.

Thanks