Last Defense for IAQ – Clean Condensate Pans

Indoor air quality (IAQ) is directly affected by the building’s mechanical air conveyance system. This article will address mechanical hygiene of the air handler unit and proper maintenance.

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By Tony Febbraro, Indoor Environmental Quality Consultant (Contributing Author to CRT)

Indoor air quality (IAQ) is directly affected by the building’s mechanical air conveyance system. The degrees of cleanliness of outdoor (fresh) air and recirculated (return) air will determine the amount of airborne and settled dust that enters the occupied space. The air conveyance system can be divided into two basic components: the Air handler unit (AHU) and the duct system. This article will address mechanical hygiene of the air handler unit and proper maintenance.

The primary components of the air handler unit are: filters, conditioning coils, condensate tray, blower assembly and internal insulation. Any of these will promote microbial growth and/or dust distribution.

The amount of moisture in the AHU will determine the environment conditions that promote mold and bacteria growth. These microbes may either be brought into the air conditioning system or will grow on unclean and damp or wetted surfaces in the air handler unit.

Dust contains a variety of materials. Outside source dust will contain mold, bacteria, pollen, silica (sand), biodetritus. Proper air handler hygiene maintenance is important for minimizing these pollutants.

The condensate tray provides the primary reservoir for microbial growth. Water collected here comes from condensed water off the cooling coils. This water has been wrung out of the air and collects any fine dust from the cooling coil fins. Over a short period of time, an untreated tray will accumulate enough fine ‘dust’ to cause two results: clumping of debris and microbial growth.

Clumping debris can a) clog the condensate tray and b) provide a food source for microbial growth. Even with very efficient filters, dusty will find their way into the air handler unit. Degraded internal insulation (fibrous glass or rubber) will release debris. In draw-thru systems, leaking or improperly sealed access doors will also allow unfiltered air into the blower chamber.

Clogged condensate trays will cause more moisture to accumulate on other surfaces including internal insulation and blower fan blades. This moisture will further collect ‘dust’ and promote microbial growth (amplification).

So it becomes apparent that a key component of the air handler unit is the condensate tray. It is the last defense of the AHU in providing acceptable indoor air quality.

Given the above, what do we look for in condensate tray hygiene?

  • Clumping or accumulation of dust/debris
  • Clogged condensate drain plug lines
  • Visible microbial growth

As air circulates through the AHU continuously, it is not likely that scheduled annual or semi-annual cleaning is sufficient to keep conditions acceptable. Treatment of the AHU needs to be on a continuous basis.

In our inspections across the country, it is easy to see the effects of poor hygienic maintenance. The common culprit is the condensate tray, often negating all the other ‘good’ conditions observed. Similarly, it is very easy to see the effects of a properly maintained system. Treated condensate trays have little to no accumulation of debris, microbial staining, corrosion or discoloration. These systems provide the best available indoor air quality.

Treatment limitations

Treatment systems come in many varieties. Some systems will focus on debris accumulation and are dispersants, usually some detergent. Others will focus on biocide abilities, ignoring the ability of molds and bacteria to ‘hide’ inside accumulated debris. Also note that what may kill bacteria can provide ineffective for molds. Some systems may work, but only for short periods of time as they are ‘spent’ with the first significant water condensation. In this case, you would prefer a slow time-release product to limit the amount of manual servicing or replacement.

Harmful to other components

Few people realize that certain chlorine-based treatment products, while effective against many microbes, may have adverse effects on rubber components including belts, seals and even rubber roof systems. Some products may have an extreme pH that can also affect (corrode) the metal tray.


Certain products will have distinctive ‘colors’. It is not unusual for certain table products to leave significant yellow stains both in the tray and all along the roof.

Optimum treatment

Proper hygienic maintenance of the condensate tray therefore requires that all conditions be addressed: clumping, biocide, pH, long lasting and aesthetics. While you may be able to purchase multiple products, the preferred products will have most or all of these features.

The main product observed in well maintained systems is Algae Guard by Controlled Release Technologies. After years of building inspections, this product has demonstrated itself as the most effective in addressing the four categories we described.

The product is used in main air handler units on both rooftops and mechanical rooms. The Algae Guard slow-release system contains detergents for dispersing debris, near-neutral pH to limit corrosion, and an EPS registered biocide that addresses both mold and bacteria and is non-odorous or staining.

Facility Environment Partners recommends this type of product often to maintain good AHU hygiene as well as bring less hygienic units up to acceptable levels.

See you next time on HVAC Preventive Solutions.

Tony Febbraro has been doing building studies since 1987 across the eastern United States. He is a Certified Indoor Air Quality Professional and president of Facility Environmental Partners, LLC, a consulting firm based in Florida.

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