Many forces are at work against and within a building. Some include wind, stack effect, duct leakage and even exhaust fans. These forces cause changes that create positive and negative pressures inside and outside of a building. An air boundary, or air barrier, is used to control airflow and control the loss of conditioned air. Conditioned air is air that has been heated or cooled by a heating, ventilating and air conditioning (HVAC) system and is used for temperature control of a living space.
It is important to understand the benefits and purpose of an effective air barrier. One can hardly overlook the importance of comfort and durability of a living space. Common issues relating to improper air boundaries and pressure imbalances include drafts, whistling, noises, doors slamming, and unusually hot or cold rooms. One important step in recognizing the actual cause of the issue is to determine which way the air is moving. Problems are commonly related to airflow and pressure differences. An example of this is slamming doors. In a building with poorly balanced heating and cooling systems, pressure differences between two rooms can cause doors to close when the HVAC comes on. Be sure to examine the carpet under the door. If it is discolored, it is most likely due to dust in the air that is being pulled under the door and into the room with the low pressure. Bear in mind, that not all leaks and pressure issues are created equal. In fact, they are usually various and cumulative. Fixing some problems here and there might just make others worse.
Another important aspect of a proper air boundary is related to energy efficiency, which is increased when the air boundary is continuous and properly aligned. This is a very important part of any efficiency strategy and is accomplished by controlling air exchange and minimizing needless losses of conditioned air.
One of the most important is related to the health and safety of building occupants. Combustion safety, in particular, is a major concern when a building is under negative pressure. This condition leads to backdrafting and flame roll out of appliances that burn natural gas. These exhaust gases get sucked back into the building instead of ventilating. These flue gases are harmful and potentially fatal. They contain carbon monoxide which is odorless, tasteless and colorless. The human senses are unable to detect it, which is why it is known as a silent killer. Therefore it is imperative that proper ventilation and positive pressure cause flue gasses and pollutants to be pushed out as intended.
It is important to determine the severity and locate the source of the imbalance. A blower door is generally used to test an entire building, depending on size. In many instances an energy auditor will use a thermographic camera during a more detailed inspection. Duct testing is used for just that, testing the ductwork. ENERGY STAR states, “In a typical house about 20 percent of the air that moves through the duct system is lost due to leaks, holes, and poorly connected ducts. The average homeowner spends more than $600 on space heating and cooling each year. Tightly sealed and well insulated ducts… can reduce annual utility bills by $120 or more.”
A professional energy auditor will create an action plan that identifies needless losses of energy and pressure imbalances while ensuring that the improvements are in line with building occupants’ health and safety.
