Q: We recently had our gas pack unit's semi-annual checkup (it's about 8 years old), and were shown some mold that had collected inside the unit and at the entrance of the ductwork. They recommended we install a UV purifier at the entrance to the ductwork for $1600 and a Lennox air cleaner at the entrance to the unit for $980. This is a very expensive solution and we would appreciate a second opinion. Is a little mold normal, and is it necessary to have all this done, or is there a better solution?

A:This a difficult question with the information provided. A “little” mold is not usually a problem or uncommon. But if you or anyone who might be exposed is sensitive or immune compromised the level of seriousness changes. This is particularly true if the type of mold present is one that can be pathogenic.

The air cleaner and ultra violet purifier may not be effective and certainly do not address the reason the mold growth is present. They may be the right solution if a solution is needed and if the conditions producing the mold growth can’t be prevented. Mold requires moisture and a substrate to grow on. If the surfaces are kept reasonably clean (the semi annual check up should involve cleaning) then mold will have nothing to grow on. Moisture is usually held in check by dehumidification. If the surfaces that are supporting the mold growth are properly insulated and the humidity is kept under control then microbial growth should be minimal.

Finally, are the people recommending the new equipment competent to determine that which is being call mold, is in fact mold? Dust deposits can occur when moving air generates static electricity (this is what we see on supply diffusers frequently). It is not mold (although if the humidity is high enough it can cause it to grow).

Mark Goldman is a senior air quality scientist for Engineering and Fire Investigations (EFI), a firm that provides mold investigation and indoor air quality services nationwide.

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