What Is a Soffit Duct?

General Description

• Soffit has an interesting word origin. The term comes from the 17th century Italian word for ceiling, "soffita." More specifically, soffita and its male form, soffitto, are a combination of two Latin roots, "under" and "to fasten." This combined meaning, "to fasten under," fits the modern usage very well, for soffits are often installed just under interior ceilings and exterior eaves. Sometimes the air in these places remains stationary, but more and more, architects and heating/cooling specialists are using these enclosed passages as tunnels for currents of moving air.

Forced Air and Cold Air Return

• In most forced-air heating systems, metal duct work connected to the furnace is routed to various rooms and heating vents. Many times soffits are built around metal piping to hide the unsightly heat conductors. This kind of soffit usually is built with a wood frame, covered with sheetrock and painted to match the color of the walls and ceiling. Not only does this structure hide the metal, but it provides a dead air space around the duct, which adds insulation value.

Cold Air Returns

• To maintain pressure, a furnace or condenser needs to pull cooler air through the house and into the central unit. Empty soffits function well with this task as they can be placed in various places around the house to allow cooler air to return to the furnace. Since hot air rises and cool air settles, many return vents are located on or near floor level. Sometimes this air movement is aided by the strategic placement of exhaust fans that switch on and off as the need arises.

Old Houses

• In a new house, architects and heating engineers often collaborate to create a built-in heating/cooling system that is well-hidden within the structure. An old house is a different story, because the original design was seldom meant to hold a forced-air heating and cooling system. When retrofitting one of these old gems, the goal is not only to balance the forced air with the return, but to make the duct work as inconspicuous as possible. This is where soffit ducts are most useful and sometimes obvious.