HVAC agglomerates are particle clusters that are formed in the HVAC sytem. There are two basic sources for these particles. One is the filter medium where the particles are agglomerated on the surface of the filter. These particles are knocked loose during filter change-out or if a hole is created in the filter. The other source is the slow accumulation of particles on the wall of the HVAC duct. These particles start typically as diffusional deposits. As they first accumulate on the wall they create an isolated stactic charge. This attracts more particles and the agglomerate begins to grow. It continues to grow until its mass is sufficient that vibration in the duct jars the agglomerate free and it becomes part of the air stream. These agglomerates are generally dominated by soot particles and are quite dark in appearance. At times they may be dominated by a local activity, such as remodeling, and take on a different appearance. Agglomerates That form in the recycle loop of the HVAC system will include skin flakes and typical indoor particles rather than the pollens, fine minerals, insect parts, tire wear, etc. associated with the fresh air supply duct.

Remodeling agglomerates are particle clusters that indicate remodeling activities. These particles may agglomerate during a cleaning activity or they may agglomerate in the HVAC system. Their characteristic property is that they consist of particles like plaster, paint spheres, glass fiber, sawdust, and other particles associated with the remodeling activity. These particles may be associated with health complaints.