chimney cap

I plan on hooking up a Harmon PF100 furnace to a 6" double walled stainless chimney. It is the only thing on that chimney. My question is do I have to have a special cap to that? I currently have it capped with a "cage" with top over it. It is not what I see on the on the websites for the stoves/furnaces. Do I need the cap or is what I have good enough?

Thanks

Your typical Class A style cap should work fine. It just needs to keep the weather and animals out and still let the appliance "breath."