I'm installing a direct vent fireplace with horizontal venting (straight out the back through the exterior wall). The problem is the vent extension is too long. Since it has a dual piping for intake and exhaust I thought it might require a special tool to cut and shorten them? The fireplace side has interlocking grooves but the other side (that connects to the termination cap) does not. That side is what I will cut down. Any thoughts? Tin snips. Mini cut-off saw? Chop saw with metal cutting blade?