I recently replaced an ~8 year old Heatilator Direct Vent Gas Fireplace with a new Lennox Fireplace. Both are Multi-sided, and 38,000 Btu. The Heatilator used 5"x8" DV venting, and of course the Lennox requires 4"x7" Secure Vent.

Is there an adapter availiable that I can utilize to go from the 4"x7" from the appliance, to the existing 5"x7" venting? Also, other than the fact that Lennox chooses to use the Secure Vent, is there any specifications related to exhaust vs intake that I need to be aware of?