If you are smelling your upstairs neighbor's food through the AC/heat vents, it is possible that there could be some interconnectedness in the ventilation system that is allowing odors to travel between units. While maintenance has told you that the ducts are separate, there could still be certain conditions or issues that are causing the odors to transfer. Here are some possibilities:
Leaks or Gaps: Even if the ducts are supposed to be separate, there could be leaks or gaps in the ductwork that are allowing air and odors to pass between units. Ducts can develop holes or separations over time due to age, poor installation, or damage.
Shared Return Air: While the supply ducts may be separate, it's possible that the return air system is connected or has gaps that allow odors to circulate between units. Return air vents draw air from the living space back into the HVAC system, so if there's a shared return path, odors could be carried to other units.
Stack Effect: The stack effect is a phenomenon that can occur in multi-story buildings. It happens when temperature differences between floors create air movement in the building. If the stack effect is strong enough, it could potentially draw air and odors from one unit to another.
Poor Ventilation Design: The ventilation system's design could be flawed, allowing air to mix between units. This might be an issue with the building's overall HVAC design or improper installation.
It's essential to address any potential ventilation issues, especially during an airborne pandemic, to ensure that air is not being shared between units. Shared air can increase the risk of airborne transmission of viruses and other contaminants.
If you are concerned about the situation, you should discuss the issue again with your building's maintenance team or property management. They might need to conduct a more thorough inspection of the HVAC system to identify any interconnections or leaks. Additionally, you may consider installing air purifiers in your unit to help reduce airborne particles and odors, providing an extra layer of protection during these times.