Well, here's why I asked..... I got Joe L's latest ASHRAE thing, he has a glossary of terms, and he lists this as the term applying to any fan vented appliance where the vented air is from inside the pressure barrier, i.e., any Cat IV appliance that uses interior combustion air or a power vent water heater. He lists direct vent as any appliance where the vented air is from outside the pressure barrier, which is what I understand to be correct. Because before, I agreed with you guys. Now, I don't know. Kibbel's explanation would be in line with Joe's, near as I can figure.