When I was shopping for an EPA-certified ZC fireplace/stove, I noticed that several brands offered optional kits to hook up directly to existing forced-air ductwork. In fact, I chose the Security BIS Ultima in part because of this. The kit is basically just insulated flex duct, an inline blower, and adapters; the flex attaches via an adapter directly to the outer shell of the unit (which is to say it draws the air immediately surrounding the firebox) and the other end connects to the supply plenum (not the return). You run both the inline blower and the main house blower to distribute the heat. But I see all the recent threads about how it is both unsafe and against code to add returns near a wood stove; is there something about these kits that is fundamentally different? How can manufacturers offer unsafe and illegal options? I bought the kit, but I guess I'll limit my use to when I'm awake; if the inline blower isn't running then there isn't much of a path for smoke to travel from the fireplace to the house ductwork since the flex goes downwards. This may all be moot (if a bit expensive), because the limited experience I've had with the Ultima (it's been too warm to burn much so far) indicates a much greater natural convection throughout the house than the closed floorplan and my previous experience with a heatilator-type fireplace would indicate.