| Safety Goggles | Your eyes are vulnerable. Here is how to protect them. |
| Sealed Combustion | A system in some furnaces, boilers, fireplaces, and water heaters that is immune to pressure imbalances in a house because it draws combustion air from the outdoors into a sealed chamber and expels by-products to the outdoors. |
| Secondary Ventilation | Ventilation for the quick removal of air pollutants from near a source. See also local-exhaust ventilation. |
| SEER | Seasonal Energy Efficiency Ratio (SEER). |
| Sensible Heat | The amount of heat involved in raising or lowering the temperature of air, not including any heat required to cause water vapor to change state (e.g. from a gas to a liquid). |
| Sensible Recovery Efficiency (SRE) | A measurement, that does not include latent heat recovery, used in determining the amount of energy passed between airstreams in a heat or energy recovery ventilator. |
| Separation | The principle of isolating pollutants from the living space. |
| Shaded-Pole Motor | A type of low-cost, usually inefficient, motor whose starting torque is provided by a permanently short-circuited auxiliary winding. |
| Sheathing | Sheathing adds strength and wind resistance to house walls, and is now made in a variety of materials. |
| Sick Building Syndrome | The term "sick building syndrome" (SBS) is used to describe situations in which building occupants experience acute health and comfort effects, but no specific illness or cause can be identified. |
| Single-Port Ventilator | An exhaust device having only one suction connection for a duct from the living space. See also multi-port ventilator. |
| SIP or Structural Insulated Panel | Structural insulated panels (SIPs) are high performance building panels used in floors, walls, and roofs for residential and light commercial buildings. |
| Solid-state lighting (SSL) | Solid-state lighting (SSL) technology uses semi-conducting materials to convert electricity into light. Light-emitting diodes (LEDs) are an example. |
| Sone | A linear unit of sound measurement used to express sound intensity. Two sones are twice as loud as one sone. |
| Sone Rating | A sone is a measurement of loudness typically applied to ventilation fans. |
| Sound Attenuator | A device, similar to an automotive muffler, that can be used to absorb some of the sound generated in a ventilation system. |
| Source Control | The principle of using nonpolluting materials in the living space, or of removing polluting materials from the living space. |
| Spillage | A situation where some of the combustion by-products spill into the living space, rather than go up the chimney, usually due to insufficient draft. |
| Spot Ventilation | Ventilation for the quick removal of air pollutants from near a source. See also local-exhaust ventilation. |
| Spray-On Insulation | Insulation products that start out as a liquid, but end up as a solid. |
| Squirrel-Cage Fan | A ventilating fan with blades resembling a squirrel cage or hamster wheel, often used in furnaces and ventilating devices. |
| Stack Effect | The naturally occurring phenomena of warm air exerting pressure on cooler air that results in warm air rising. |
| Stale Air | The air leaving a house through a ventilation system. |
| Static Pressure | The amount of pressure exerted against the walls of a duct or airway, created by the friction and impact of air as it moves. |
| Static Pressure Drop | The change in pressure resulting from resistance to airflow. |
| Strain Hygrometer | A relative-humidity sensing device containing a spiral-wound material that is sensitive to changes in relative humidity. |
| Supply Air | The air entering a house through a ventilation system. Also, the conditioned air passing from a furnace/air conditioner into the living space. |
| Supply Grille | A grille through which fresh air enters a room. See also Exhaust grille. |
| Supply Ventilation | A general ventilation strategy that uses either a supply ventilation fan or a forced-air heating/cooling fan to draw air into a house. |
| Supply-Only Ventilation | A general ventilation strategy that uses either a supply ventilation fan or a forced-air heating/cooling fan to draw air into a house. |
| Synergism | The interaction of two substances such that the combined effect is greater than the sum of the individual effects. |
| System | The dynamic interrelationship of components designed to fulfill a purpose. |
