This is looking into an HVAC air intake register, where your air filter goes. The pipe is the natural gas water heater exhaust. It penetrates the duct below, and follows it up into the attic. This is a major hazard and has never been allowed. If there is a breach or damage, exhaust and carbon monoxide will enter the HVAC system. This wouldn’t have been discovered until someone went to replace an HVAC filter.
Cary North Carolina Home Inspector!