Quality Air Consultants - HVAC Service -(Continued) - Port Wentworth, GA
Quality Air Consultants -Savannah's Pro's -  "Leaders in Solutions for a Healthy Indoor Environment"
Duct Board- It can be used to make an air-box- it is stiff, has a foil backing but look at mold growth on surface during mold remediation
The IAQ Battle: Duct Board Vs. Metal
The battle of mold in residential duct systems presents an interesting question: Given the exact same condition variables (size, distance from plenum, identical relative humidity conditions, etc.) would a length of duct board attract more or less mold than its metal counterpart?
At this point there's not enough research to answer the question, but generally if a choice exists between duct board and metal for ultimate IAQ, many experts believe metal duct is the better choice. Duct board manufacturers have produced studies that claim duct board attracts no more mold than metal. While the jury is still out on mold, it's scientific fact that metal duct has less pressure drop, has a smoother surface that's less likely to accumulate dust, and is easily cleaned with a hard surface biocide if mold occurs.
Another disadvantage to duct board is the seams sometime leak over time, which could be due to aging tapes or installation error. Duct tape is not approved for any ductwork and foil tape tends not to hold as long as mastic/cloth tape combination.
These openings created by the connecting tape's failure to adhere over the life of the duct, creates voids that can expose the cold air supply to warm humid condensation-creating conditions outside the duct. Where there's moisture, there's a good chance mold will develop. That's why the moisture source—whether it's a leaking pipe, roof or condensation-collecting void in the ductwork connection—must be rectified.
**The duct board spoken of above; it gets wet from condensation and moisture like a sponge and air borne spores adhere to it as this unit was only two years old. It is a natural home for fungal growth and accelerates the reproduction and amount of spores that are expelled.  This is what your airways look like inside of the unit creating the “conditioned air you breathe in your home.
It should be bright yellow on the front of the board that was cut out of the supply plenum.
Supply Duct going out of unit in #3 during mold remediation on HVAC 

This is the same plenum with sheet metal, and the insulation on the outside of the airway. This supply plenum is 7-8 years old and still clean and sanitized.
A homeowner complaining of respiratory problems should have the home's RH determined, because mold/mildew can't exist without moisture. This is accomplished with either:
  1. determining wet bulb and dry bulb temperatures and calculating RH with a psychrometric chart;
  2. using a humidistat;
  3. documenting an extended period of RH readings with a humidity recording instrument to determine house's tendencies;
To lower the RH, the air conditioning system should be turned on. Much of this boils down to a humidistat and educating the homeowner on using the air conditioning unit to control RH regardless of whether the indoor temperature is cool enough or not. This is particularly important in summer months if the home is unoccupied for extended periods.
Setting the thermostat lower will reduce RH, but it also tends to chill the home's occupants. There are thermostat/humidistat combinations that when set for 55-percent, will run continuously until the RH set point is achieved, regardless of whether the space temperature is too cold in the house. If the occupants complain about the low temperature in the conditioned space, an air comfort solution to the chilling effect is an installed humidity control board. While not efficient this reheat control board activates the furnace to reheat the air when the space if the temperature is too chilling while achieving the targeted RH. A humidity control board is easily wired into the thermostat wiring anywhere between the thermostat and the fan coil unit and works with essentially any a/c or heat pump models.
An oversized air conditioner might be the cause of a high RH because it's not moving enough air across the evaporator coil. Its oversized cooling capacity achieves the set point room temperature too quickly (short cycling) without running long enough to circulate sufficient air across the evaporator coils to remove the humidity at the evaporator.           
Another remedy for oversized a/c units might be adjusting the blower motor speed (for fixed speed units). For example, increasing blower speed will move more air across the evaporator coil, which in turn circulates more air. However if the blower speed is increased too high, the evaporator air exit temperature might be above the dew point temperature and there will be no condensation or moisture from the air. The key is to look at the evaporator air exit temperature. Once the evaporator coil is at steady state temperature, determine if the evaporator air exit temperature is below the dew point. If it is well below the dew point, increase the blower speed. If it's above the dew point, decrease the blower speed to dehumidify. Fan speed can be adjusted by moving a fan lead to a different position or using a different fan-power lead (refer to equipment instructions). The downside of increasing motor speed is the fact that fan noise increases.
EPA Certified Logo, Environmental Protection   There are two reasons why the HVAC contractor should provide IAQ services to their clients, the contractor's realm of the HVAC system can both create mold and also prevent it. Thus it should only be the certified IAQ/HVAC contractor that should remedy the homeowner's IAQ problems.