I have lots of my auditing customers who ask me about duct cleaning, and if they should do it. It seems like the only way to get them really clean is with some sort of roto brush, but it also seems like that process is going to possibly do more damage than good. Obviously this really depends on the duct system and the quality of the craftsmanship, but I was just looking for the Pro's opinions. Thanks!
The dew point temperature is so close, that it only takes a very few degrees of rise in duct temp that there is no chance of condensation. Add to that the fact the duct surface temp will always stay warmer than the air temp coming into it, there is again, no chance for condensation to happen unless it is from much higher humidity air coming from the exterior of the duct.
There is not a "Reply" button on the last post. So I came back up to this post since it contains the statements about theory vs data not matching means keep the data and get a new theory.
Attached are two pictures showing mold growth in residential and commercial supply air ducts. These are examples of what I find every time I open up a supply duct. Your "theory" is that this does not happen. The data shows it is very very common. In fact if you google "mold in supply ducts pictures", I find pictures where others have found the same thing (that's how I found these). Those pictures indicate this is common all over the US - even in drier climates like San Francisco and Kansas (not designated as humid climates by ASHRAE).
Best of luck to you. This horse is dead.
First of all, I certainly did not mean to imply it never happens, it certainly can and does happen, just not for the reasons you suggest.