Stack Effect

When the lower part of a house is depressurized in this way, air enters through cracks and holes located over the building envelope below the neutral pressure plane. In this situation, the house substructure is under negative pressure and creates suction on the surrounding soil. This convective current of warm air rising and makes the house behave like a chimney.  In fact, this temperature-driven airflow is often called the stack effect, as it is powered exactly the same way as the draft on a chimney. As a chimney draws air in at the bottom, it forces the air out the top, which results in a neutral pressure plane somewhere along its length.

Stack Effect in Winter

Warm air is more buoyant
than colder air.  As heat
escapes a roof, cold air is
sucked in through the
basement and first floor
windows.

Stack Effect in Summer

 The reverse happens in summer
when hot air outside of an
air-conditioned house can push
cooler indoor air down from the
ceiling and out of cracks in
the basement.

Stack Effect and Indoor Air Pressure

• Stack effect also affects the indoor air pressure and Neutral Pressure Plane [NPP].
• Neutral Pressure Plane
  • A place in the house where indoor pressure is equal to the outdoor pressure.