Is Mold a Winter Problem?

Org Published 1998

Down here in south central Florida right now it is about as winter as it gets. A lot of nice days; some cool (in 40s). Humidity is about as low as we see it which is still high for much of the country (normally above 60%). For much if not most of the rest of the country, however, things are a good bit different. Temperatures stay below freezing for weeks on end, humidity is well below 50% virtually all of the time. As a result, mold growth is not a concern for most of us at this time of year. Or is it?

We have learned that growth of bacteria and mold is very rapid when humidity is above 60% and it is warm. Here in Florida we see dramatic evidence of this during the summer. Mold grows on the sides of our buildings, sidewalks, plants, and almost everywhere exposed to the heat and humidity during the summer. At this time of year, we can relax and not clean our patio furniture and other outside surfaces so often. Growth has slowed down if not totally stopped.

Growth Is Low In The Winter

In addition to being appreciative of the unexpected business, we were curious as to why there would be so much need for mold control products in areas of the country where growth was normally not thought to be a concern. We began to pay close attention to orders from those areas. We asked customers about the needs that led to their purchases. In some cases, we were told of water leaks that had led to gross levels of growth. In most cases, however the customers cited the same situations we experience in the south. The main difference seemed to be that our summer growth is easy to see. This is the case whether it is on a patio lounger or in an HVAC air handler. When you look at it there is little doubt as to what you are seeing.

All of our customers cite concerns for health and comfort caused by mold and bacteria in indoor air as their main reason for using growth control products. In the case of northern customers, however, their concerns normally are related to actual tests that show what seems to be an excessive level of organisms. These tests are what lead to the buying decision. Here in the south, in contrast, mold control is more likely to be a normal part of system maintenance. The problem is so obvious that control measures are accepted as normal. Thus it has began to appear to us that the problems are not related to climate. They are universal. The difference is that humidity belt residents are more prepared to recognize the problems because of the conditions they see outdoors every day. So, if mold is such a universal air quality problem, why haven’t we heard more about it?

The IAQ/Health Debate

Until very recently, indoor air quality has not been considered a health matter. Poor indoor air quality was seen as something that could be distracting, uncomfortable, and lead to low productivity. It was not seen as a threat to health except in the most outrageous cases. As a result, little research was done to better understand the role of microbial growth and indoor air quality problems. It was felt that if growth was important, health would be more of an issue because microbial growth clearly can affect health.

When work started in ASHRAE committees on revisions to Standard 62-1989, a question posed early on was what effect, if any, poor indoor air has on health. Eventually this became one of the most important debates involved in updating the standard. As the topic was discussed, it soon became apparent that most experts believed that poor indoor air quality has a very negative effect on health. Some even called for the standard to become a health standard rather than just a ventilation standard. Everyone conceded that there is little that is helpful in the present research literature.

The debates that have taken place have led to much new research, that is producing some interesting information. It adds to our belief that growth is a major cause of IAQ problems. Research that will conclusively demonstrate the relationship between biological air contamination and health is complex and time consuming, however. It may be many years before the proof that many want is available. Even so virtually everyone associated with IAQ believes there is a considerable linkage between health and microbial growth. The only question is whether the health effects are limited to allergies, colds, and other temporary conditions or are they more permanent and debilitating.

Winter and Cool Climate Growth

So, the answer is, Yes! There is growth during the winter and in cool climates that causes problems in HVAC systems. This is because the inside of the HVAC system has a climate of it’s own that is independent of either the outdoors or the building the system serves. The introduction and removal of heat, humidity and creation of rapid air movement through the system creates a micro climate that can be quite different from the outside air conditions. This climate system also changes from hour to hour creating conditions within the air handler and ducts that alternately promote microbial growth.

With proper maintenance, these continuous mini climate changes will not lead to excessive growth. More often, the result is a buildup of increasing levels of contamination until it reaches a concentration that causes problems. More and more contractors are finding that in order to maintain an acceptable level of indoor air quality (and possibly health) for their customers, they need to include the prevention of growth as part of their maintenance offering. Those services must be included year round because the mini climate inside the HVAC system has winters and summers independent of those of the outside world.

Bob Baker is a member of ASHRAE and Chairman and CEO of BBJ Environmental Solutions, Inc., a manufacturing company specializing in providing clean air through environmentally responsible products, such as BBJ MicroBiocide, BBJ Micro Coil Clean, BioSoft Spray Disinfectant/Cleaner, and Fresh Duct, as well as The Indoor Air First Aid Kit.