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EPA Moisture Control Guide 2013

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www.epa.gov/iaq/moisture Appendix D – Air Pressure Mapping the other port (with no tubing) senses the pressure in the room. The micromanometer reads the pressure difference. The minus sign on the micromanometer interface indicates that the room is under negative pressure relative to the other side of the door. Air pressure mapping is used to determine whether air is moving through a building in a manner that contributes to condensation problems. Unplanned airflow will cause problems if either: • Air is moving from the warm side of an exterior wall, the ceiling, or the basement to the cool side. Figure D-2 shows the pressure map of a building that consists of a single room with an operating 100-cfm exhaust fan. The room is depressurized 4 Pascals by the exhaust fan. The exhaust fan is represented by a box with an X in it and an arrow showing the direction of airflow out of the building. The line with an arrowhead on one end and a circle on the other signifies that air is being drawn into the building from outside. • Cold air is blowing from an air conditioning diffuser into a space where humidity is high. To generate an air pressure map of a building, use: • Floor plans showing the layout of each floor and the location of air handlers, supply diffusers, return grilles, and exhaust grilles. • A micromanometer and flexible plastic tubing to measure pressure differences between indoor air and outdoor air, rooms and corridors, room air and plenum air, and room air and building cavities. This procedure can be applied to more complex buildings and airflows to document air pressure differences between rooms, indoors and outdoors, attics, basements, crawlspaces, utility chases and wall and ceiling cavities. Figure D-3 illustrates a pressure map of a more complex building when the air handler is running, the exhaust fans in the bathrooms are running, there is no wind, and all the interior and exterior doors are closed. • A smoke bottle to determine the direction of air flow. As depicted in Figure D-1, use a micromanometer to measure the pressure difference across a closed door. Note that the tubing is run from one port of the micromanometer to the far side of the door, while D-1

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