Let's look at what we do know. First, insulation in ducts provides noise control - and this is an important consideration. Air quality isn't the only thing that affects the indoor environment; noise is an important issue as well, and excess noise can lead to a general dissatisfaction with IEQ (Indoor Environmental Quality), which people often confuse with poor indoor air quality. Also, it is clear that any sufficiently wet and dirty surface can support microbial growth. However, it's not so clear that this entails an attitude that there's no difference in what you use in ducts.

We have seen no evidence that duct liner and unlined duct are equal in their propensity to support growth. That should be an important consideration. Also, there are differences among various types of liner and even between many liners of the same brand. It would seem important to know what these differences are, so that designers and building owners and managers can make informed decisions. Logic would dictate that porous duct liner has a greater propensity than non porous materials to trap and hold both dirt and moisture - just as so-called "fleecy surfaces" in an office space do the same thing.

The question then becomes whether the benefits of insulation for noise control outweigh the dangers. Some are correct in saying that the task should be to keep excess dirt and moisture out of HVAC systems. However, this isn't happening on a broad scale. Current systems do seem to be prone to just the sort of contamination that contributes to microbial growth.

One problem may be the "out of sight, out of mind" phenomenon. If facility managers don't know whether there is dirt and moisture in the ducts - whatever the lining may be - they are less likely to take steps to remediate it. Another factor may be that facility managers don't appreciate the scope or severity of the problem - not realizing what will happen if potentially contaminated duct liner is left in place and not removed and replaced according to NAIMA's (North American Insulation Manufacturers Association) directives.

A question for designers and managers is whether they should design buildings for a best-case operation and maintenance scenario. Should designers assume that facility managers will maintain the building and its systems in a certain way, when evidence seems to point to the fact that many don't?

A more important question is the financial burden involved with removing and replacing contaminated duct liner. The effort and expense involved with that may lead some facility managers not to take wet and dirty duct liner seriously - or not look close enough for signs of contamination. Again, logic would dictate that cleaning unlined duct would be easier and cheaper than removing and replacing contaminated duct material, but the financial trade-offs would be for each building owner to decide.

What's the bottom line? It would seem that the responsibility does fall on the facility managers and operation and maintenance staff. They need to be aware of what materials are in their systems - whether lined or unlined - and to keep an eye out for the conditions that might lead to microbial growth. If those conditions exist, then the only recourse is to adequately clean the ducts if unlined, or, if lined, follow NAIMA's (North American Insulation Manufacturers Association) recommendations to remove and replace the insulation. To ignore potential or existing microbial contamination is to invite IEQ (Indoor Environmental Quality) problems.

Author's Bio: 

Julian Arhire is a Manager with DtiCorp.com - DtiCorp.com carries more than 35,000 HVAC products, including industrial, commercial and residential parts and equipment from Honeywell, Johnson Contols, Robertshaw, Jandy, Grundfos, Armstrong and more.