CMI HVAC Systems and Mold Growth

Question 1

Mold growth in an air handling unit (AHU) is most commonly found in which location first?

Accepted Answer

The evaporator coil and condensate drain pan where moisture accumulates

Answer

Supply air ductwork downstream of the coil

Answer

The return air plenum far from any moisture source

Answer

The outdoor air intake damper during dry weather

Question 2

A clogged condensate drain pan in a fan coil unit creates conditions for mold growth primarily because:

Accepted Answer

Standing water in the pan provides sustained moisture and organic nutrients for fungal growth

Answer

It causes the coil to freeze, releasing mold spores into the air stream

Answer

It increases supply air velocity, spreading existing spores further

Answer

It causes the refrigerant charge to drop, reducing cooling efficiency

Question 3

Which HVAC filter MERV rating is the minimum recommended to capture most fungal spores (3–10 microns) in a commercial building?

Accepted Answer

MERV 11–13

Answer

MERV 1–4

Answer

MERV 6–8

Answer

MERV 16+

Question 4

Flexible ductwork lined with interior fibrous insulation presents a higher mold risk than sheet metal ductwork because:

Accepted Answer

The fibrous liner retains moisture and provides organic substrate for mold colonization

Answer

Flexible duct always has higher air leakage rates

Answer

Flexible duct is not compatible with UV germicidal lights

Answer

Sheet metal duct is always cleaned annually per NADCA standards

Question 5

During a mold inspection, the inspector finds visible black growth inside a supply air diffuser. The most important diagnostic next step is:

Accepted Answer

Inspect the AHU coil and drain pan as the probable source, and collect samples from the diffuser and upstream

Answer

Immediately recommend full duct replacement without further investigation

Answer

Clean the diffuser grille only and consider the problem resolved

Answer

Increase filter changes to monthly and re-inspect in 90 days

Question 6

UV-C germicidal lights installed in HVAC systems are most effective when positioned:

Accepted Answer

Directly at the evaporator coil surface to continuously irradiate biofilm and prevent mold colonization

Answer

In the return air duct just before the filter

Answer

Inside flexible ductwork near registers

Answer

At the outdoor air intake to treat incoming air