Fully Ducted HVAC System
by Brad Keyes, CHSP, on Feb 23, 2015 12:00:00 AM
Q: I have never been able to understand what a fully ducted heating system is and when a damper is not required. Can you explain this matter to me?
A: ‘Fully ducted’ HVAC systems are those in which the air in the HVAC system travels from the air handler to the room diffuser in ducts. The alternative is open return-air plenum ceilings or open supply-air plenum ceilings. Those types involve the open space above the ceiling for the movement of air, and there is no HVAC duct in that area. The return-air plenum ceilings are much more common than supply-air plenum ceilings, and would have an opening at the smoke compartment barrier (above the ceiling) to allow the movement of ventilation air without being inside ducts. What the Life Safety Code is saying is if you have ‘fully ducted’ HVAC system from the air handler all the way to the room diffuser on both the supply and return sides, and it penetrates a smoke compartment barrier, then the LSC does not require that you have a smoke damper in this barrier if the smoke compartments on both sides of the barrier are protected with sprinklers. While this is a huge benefit for facility managers, if you are required to comply with the International Building Code (IBC), they do not allow this exception, and you would have to have smoke dampers at the barrier.