Well-documented set of problems in commercial AHUs/RTUs

Where biofilm (“white slime”), algae, and microbial growth develop in the condensate pan, on coils, and in the drain line. Here are the key issues with solid references:

• Drain clogs → overflow/shutdowns & hidden damage. Slime/algae in pan and drain lines obstruct flow, causing backups, float-switch trips, and sometimes unseen damage inside the unit/ducts. Guidance for hospitals flags trap/drain failures as a contamination and damage risk because problems can be hidden inside the AHU. Healthcare Facilities Today

• Microbial amplification in pans/coils (biofilm forms easily). ASHRAE notes that damp HVAC surfaces—including cooling coils and drain pans—readily support bacteria- and mold-containing biofilms unless managed. ASHRAE+1

• Odors & IAQ complaints. Maintenance bulletins and studies highlight that pans not serviced routinely will grow mold/bacteria, leading to “mildew-like” odors and IAQ issues. AET Inc.

• Energy/heat-transfer penalty. Biofilm on coils and pans isn’t just hygiene—it insulates and fouls heat-exchange surfaces. ASHRAE articles discussing UV treatment specifically target preventing biofilm establishment on coils and drain pans to maintain performance. ASHRAE

• Hospital/critical environments: elevated concern. ASHRAE Journal guidance for critical-care facilities lists fan, coil, drain pan, filters, and ductwork as locations that can harbor pathogenic microorganisms and biofilms if not regularly cleaned/disinfected. ASHRAE Dallas

• “White slime” is bacterial biofilm (not algae). Field write-ups summarizing studies show that the common white, gelatinous clogging mass in AC drains is predominantly bacterial biofilm (not algae), which protects the colony and accelerates blockage. Kobie Complete Heating & Cooling Inc.

• Code/controls implications. Because pan overflow is so common, the IMC requires secondary protection (aux pan/secondary drain or shutoff device) when units are above conditioned spaces—practically acknowledging biofilm-related overflow risk. ICC Digital Codes+1

• Inspection checklists call out algae/mold in drains. Professional guidance for diagnosing condensate problems explicitly tells techs to look for algae/mold growth as a sign of stagnant water and potential blockage. 

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