Most models can be converted to a Power Vent (pulling the exhaust from the stove), mounts on outside of house.
Yes, you can buy the power vents separately ex)FIELD CONTROLS SWG POWER VENT
Direct Vents are more common on the Keystokers, mounts directly to the appliance and pushes the exhaust fumes out and the pipe has to be sealed properly.
If you do a search on Power Vent vs. Direct Vent, you see there is a slight difference, but basically function the same.Direct vent vs Power vent...