It’s rarely the duct work. The dust that lays in the ductwork is not where…in the air!! The bottom of ducts are like filters, they collect dust. This dust will lay there unless disturbed by someone or a change in the system is made such as a new furnace/fan with more cfm/higher air velocity or the dust gets wet from a leak…then the mold will grow.
From CMHC: What Can Duct Cleaning Do For You?
A thorough duct cleaning done by a professional duct cleaner will remove dust and debris-pet hair, paper clips, children’s toys and whatever else might collect down there. Ideally, the inside surface will be shiny and bright after cleaning. Duct cleaning may be justifiable to you personally for that very reason: you may not want to have your house air circulated through a duct passage that is not as clean as the rest of the house. However, duct cleaning will not usually change the quality of the air you breathe, nor will it significantly affect airflows or heating costs
Does duct cleaning prevent health problems? The bottom line is: no one knows. There are examples of ducts that have become badly contaminated with a variety of materials that may pose risks to your health. The duct system can serve as a means to distribute these contaminants throughout a home. In these cases, duct cleaning may make sense. However, a light amount of household dust in your air ducts is normal. Duct cleaning is not considered to be a necessary part of yearly maintenance of your heating and cooling system, which consists of regular cleaning of drain pans and heating and cooling coils, regular filter changes and yearly inspections of heating equipment. Research continues in an effort to evaluate the potential benefits of air duct cleaning. In the meantime…
I have heard and seen heating companies offering duct cleaning show blown up pictures of dust mites (Note: we go to bed with these creatures every night!!!) and claim the ducts were full of them because of the dust. NO!NO!NO! Ducts are usually quite dry and sometimes very warm/hot (110-130 deg)…not much can live in them…there’s no moisture.
Where do dust mites live…in your bed or your favourite stuffed cloth covered chairs…or in the wet ear of the teddy bear that your small child chewed on. They want to live close to us since they feed on our sloughed off skin cells and need the moisture we supply to them.
I agree that there are less-than-professional companies out there who try to sell duct cleaning when it is not needed. That is not my point. Nor is dust mites.
My point, with this post, is to show that this 75 year old house, with many joist plenum return ducts, had never (that the owner’s knew of) had the ducts cleaned. There are also many materials in the ducts, besides mold spores, that could be causing the kid’s respritory problems.
The client was convinced that mold was the problem and that her house was full of mold. One of the most important thing that a trained mold inspector can do is to educate the cleint. This includes cutting through all the hype about mold and presenting the facts.
If there is a problem with mold, I point it out and provide the testing to verify what I see. If there is not, I also educate the cleint about that. I talk more people out of testing than I actually do sampling on.
BTW: Around here, ducts can get moist. People have this bad habit, during the winter, of turning their humidistat up to 50 - 60%. They believe (falsely) that the colder it is outside, the higher they should set their integral humidifier. Then they complain about window sash condensation, surface most formation and other problems.
I also recommend duct cleaning for new houses. When I check them, there is usually a great deal of sawdust, drywall mud dust and other construction debris in the ducts.
Just expanding the duct cleaning issue as the cleaners are scamming people with saying they should be cleaned very 3-5 years!! Have to arm the consumer/HI with unbiased info.
Want to keep the ducts fairly clean…keep a clean house, lift the floor supply/return grilles and vacuum duct/pan under them yearly, keep the furnace in good repair, use a bit higher quality filters (if air flows are are not restricted too much)
I, regularly, see people who want mold inspection clients whose houses are just a complete mess.
Maybe they see the HVAC system as a kind of a big central vac system :mrgreen:
They also beleive (falsely) that the furnace filter is, in some way, meant to clean the air, with regards to indoor air quality. Not true.
The furnace filter is not to protect humans from dust (or mold or sawdust or cat and dog and ferret hair or matchbox cars), it is meant to protect the furnace’s heat exchanger and A/C coil from dust and debris.
They are also totally convinced that they only have to change the filter every year of so.
Then they wonder why their air flow is so low.
Education is, most probably, a home inspectors most important job.
Can be. I spend 45 min to 2 hours with each client delivering/explaining the report, even if the client has been on site for the inspection. Have a set of brochures from gov ( mould, IAQ, energy efficiency, house ventilation, HVAC, etc) that I hand out. People are pleasantly surprised with this use of their tax $$$.