ventilation
ventilation system
ventilating system

They also usually have their own special natural ventilation system.

And now she also understood why the ventilation system was no longer working.

"But there's no central ventilation system and our tests show nothing went up to the living area."

"Has the ventilation system been started up in number one?"

Almost all you hear is the rush of air in the ventilation system.

Turning off the ventilation systems when the school is not in use, he said.

Effects of wind on the ventilation system in a building.

We've been trying to learn his route through the ventilation system.

The problem, it seems, was a fire in the ventilation system.

The ventilation system was the same, too similar to be a matter of chance.