Infiltration

When outside air enters a building, it has to be cooled or heated to maintain comfort. The more unconditioned air entering the building, the greater the load on the heating and cooling system and the greater the cost. Air can enter the building in three ways: 1) intentionally via the HVAC system (to provide fresh air), 2) unintentionally through cracks and crevices in the building, 3) unintentionally through doors and windows as they are opened and closed throughout the day. Uncontrolled infiltration may not provide fresh air where needed, and it cannot be turned off when the building is unoccupied. Wind will increase infiltration and tall buildings have a “stack” or “chimney” effect that draws air into the bottom of the building and forces it out the top. HVAC systems that have leaky ducts or do not provide fresh air to replace that exhausted by fans may cause air to infiltrate through building crevices as well. There are several methods to address unwanted infiltration:

1. Caulking and weatherstripping should be in place for doors and windows. Consider adding automatic door closers to reduce heating and air conditioning costs.
2. For open doorways (such as are often used at loading docks and warehouses), clear vinyl strips can be used to reduce infiltration.
3. HVAC system outside air dampers should seal tightly when closed. Replacement with good quality opposed blade dampers with seals at the blade edges and ends will reduce infiltration.
4. Exhaust hoods should be examined and adjusted to ensure they are exhausting the minimum air necessary to remove contaminants. Baffles can be added to the exhaust ducting or inside the hood to reduce flow.
5. Avoid using building cavities for return air paths. While not well documented in commercial buildings, indications are that using building cavities as return air paths can lead to substantial increases in infiltration rates.

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