What is the impact of negative pressure in an exhaust-only system on air quality?

In an exhaust-only ventilation system, the creation of negative pressure within a building effectively causes the building to draw air from outside to replace the air that is being exhausted. This means that if there are any contaminants, allergens, or pollutants present outside, they can be pulled into the indoor environment.

Negative pressure can inadvertently increase the infiltration of outdoor air, which may carry dust, pollen, smoke, and other airborne particles into the living space. These outdoor contaminants can negatively affect the indoor air quality, particularly if the external environment has a high level of pollution or if there are sources of contaminants nearby, such as construction sites or heavy traffic areas.

In contrast, simply exhausting air does not inherently improve indoor air quality or reduce outdoor pollutants decisively. Additionally, while managing humidity is an important aspect of indoor air quality, negative pressure does not directly balance indoor humidity but may exacerbate it under certain conditions depending on the moisture levels of the incoming air. Thus, the impact of negative pressure in an exhaust-only system primarily concerns its potential to introduce outdoor contaminants into the interior space.