Ventilation Rates Improve Performance

Over the last 10-20 years a significant battle has occurred between the green building movement and the indoor air quality movement.  The conflicts are rarely conscious, but the underlying goals of each side often create divergent results.  What is good for one is bad for the other.

Ventilation is an excellent example of this tension.  The energy efficiency crowd would prefer to maintain low ventilation rates, because ventilation decreases efficiency.  Or, at a minimum, makes it much more expensive to maintain the same level of efficiency.  Alternatively, the IAQ crowd would prefer dramatic increases in ventilation rates as a means to exhausting indoor pollutants.  Ironically, this creates a scenario where the techniques that most benefit the planet (energy efficiency) offer the least benefit to the health of the people (ventilation).

Of course, this creates a bit of a false dichotomy.  Builders have found clever methods for increasing ventilation without dramatically reducing energy efficiency.  Heat recovery ventilators (HRVs) are a great example of this.  However, the systems are not cheap, especially in retrofit projects.  Thus, unless an unlimited budget is available, a sacrifice is often inevitable.

Lately, several fascinating studies have bolstered the side arguing for increased ventilation.  The first study measured the performance of office employees in a call center.  Performance measurements were collected on items such as information processing, telephone interaction time, etc.  These measurements were collected before and after IAQ adjustments were made.  In this study, two changes were used to improve the IAQ:  1st, remove 20 year old carpet and 2nd, increase the ventilation rates. Below are the changes in performance based on these changes.

Performance improvements due to ventilation increases

Another similar study (Seppänen et al.) attempted to quantify the effect of specific levels of ventilation on performance.  Both work and school performance factors were utilized.  Perhaps most interesting was the significant improvement in performance achieved when ventilation was increased above building codes.  It isn’t just underventilated buildings that negatively influence performance, but even normally ventilated buildings may be insufficient.

How ventilation rates effect performance.

Far less research has been conducted on the effects of ventilation in a residential environment.  Much of this is due to the difficulty of obtaining objective measurement points in a non-work setting.  The most conclusive studies to date have instead focused on the secondary effects of ventilation, i.e. reduced humidity and dampness.  Many studies have found a correlation between indoor dampness and negative health effects such as asthma and allergies.  Improved ventilation, of course, can dramatically reduce the dampness of a building, and in turn, improve the health of the occupants.

According to the Lawrence Berkeley Laboratory, “the few studies that have directly investigated whether lower ventilation rates in homes are associated with a worsening of health have had mixed findings. These studies have considered only respiratory health outcomes such as asthma symptoms and wheeze. However, for indoor pollutants that have been clearly linked with adverse health effects, the reductions in indoor pollutant concentrations in homes with higher ventilation rates would be expected to improve health.”




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Duct Cleaning is a Scam

Duct Cleaning – Scam or Legitimate Service?

Every month, without fail, I receive at least 3 or 4 solicitations for duct cleaning services.  They always provide a good chuckle before I toss them into the recycling bin.   However, it recently occurred to me that many people must hire these companies or they wouldn’t keep spending the money on advertisements.  Thus, I felt compelled to provide a bit of education on the merits, or lack thereof, regarding duct cleaning.Duct cleaning scam

First, let’s just point out the obvious.  Duct cleaning companies have a terrible habit of massive upselling at the customer’s home.  Take a quick glance at the next 2 or 3 duct cleaning coupons or ads you receive.  Almost without exception, they advertise a price of around $100.  I’ve even seen some as low as $37.00.

Here’s the problem.  Even if they were running a non-profit and paying their employees minimum wage, it would still be impossible to stay in business charging only $100/house.  This wouldn’t even cover the cost of labor and gas to drive to the home and setup the equipment.  How is this addressed?  Upselling.  Massive upselling.  A typical duct cleaning project advertised as only $100 will quickly turn into a $350 project once they factor in the caveats found in the limitations.

Okay, but hey, they’re providing a good service right?

Let’s look at the science behind duct cleaning.  If you read their ads, the big problem with ducts is that they’re full of nasty accumulations of dust, mold and dust mites.  And, so the claim goes, these unpleasant particulates are blown throughout your house every time the furnace runs.

Mold doesn’t like ducts.

Duct cleaning & dirty ducts

One of the primary claims promulgated by duct cleaning companies is their ability to remove mold growth.   Is this true?  Most ducts that are capable of undergoing duct cleaning are made from metal.  Metal, of course, isn’t a very good food source for mold.  It suffers from two problems.  First, it lacks the digestible components necessary for mold to flourish.  Second, because metal can’t absorb moisture, it is unlikely to provide conditions conducive to mold growth.  Now granted, mold could grow on the dust that settles on top of the metal.  We’ll explore that next.

Mold likes moisture.

Mold growth cannot occur without available moisture.  Thankfully, the amount of moisture required by mold growth is usually in excess of the level of humidity preferred by humans.  Thus, moisture conditions conducive to mold growth only occur when something has gone awry with the home.  Many things can go wrong in a home that lead to excess moisture.  Roof leaks, plumbing leaks, poor ventilation, etc.  However, in all but extremely rare circumstances, the conditions inside your ducts will be far drier than anywhere else in your home.

Settled dust remains settled.

Why does dust accumulate in your ducts in the first place?  The answer to this is the biggest reason why duct cleaning is worthless.  The reason dust accumulated in the ducts in the first place is because the wind speed is insufficient to keep the particulates airborne.  The dust particles are moving throughout the duct system but eventually fall out and deposit onto the duct.  Why would these same particles of dust suddenly feel inspired to jump into the wind stream and float off into the home?

A scientist recently tested this and found an interesting conclusion.  Wind speeds in excess of 160mph are required to move settled dust back into the air stream.  I don’t what brand of HVAC equipment you bought, reaching these speeds within a residential duct system is impossible.  Unless, of course, you’re using a leaf blower instead…

Duct cleaning with a leaf blower.

Still not convinced?

“Duct cleaning has never been shown to actually prevent health problems.  Neither do studies conclusively demonstrate that particle (e.g., dust) levels in homes increase because of dirty air ducts.” — EPA

Caveats. Ok, not all duct cleaning is worthless.  Occasions do exist that call for duct cleaning.  These include asbestos cleanup or post construction cleanup.  Other conditions, like rodent infestation or water damage, are not conducive to duct cleaning, because direct replacement is more effective.

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Mold preventative coatings are a joke

Controversial?  Yep.  True?  Yes, with caveats.

Let’s begin with a basic review of the relevant factors that allow mold growth to occur.  In nearly all circumstances, this comes down to available moisture and food source.  Yes, we can talk about temperature requirements, but we’ve all observed mold happily growing in our 35 degree refrigerators.  In all but the most unusual circumstances, the temperatures we humans prefer to live in correlate well with the temperatures mold prefers.

First up, moisture.

Mold requires a minimum amount of available moisture to grow.  Thankfully, in all but the most humid environments, mold requires more moisture than is commonly found in our building environments.  Exceptions to this include cellars or other areas that require high humidity conditions.  One could also make the case for exterior siding in cool damp climates such as the Pacific NW, where normal buildings can suffer from mold growth.  However, in most situations, mold growth requires an unusual amount of moisture, an amount of moisture caused by a building defect.  This may be a structural defect, such as a leaky roof, or a design defect, such as poor ventilation.

Why is this relevant in our discussion of mold preventative coatings?  In short, if we properly address the elevated moisture conditions, we’ll prevent mold growth more effectively than the most advanced preventative coatings available.  Viewed this way, mold prevention coatings are a cover up solution that fails to address the underlying cause.  Ok, but what if the coatings worked perfectly?  Even if this were true (and it is not!), elevated moisture conditions cause many other problems besides mold growth.

Consider a home with elevated humidity suffering from mold growth.  Imagine, for a moment, that we apply a perfectly effective mold inhibitor on every surface in the home.  Yes, this would theoretically deal with the mold problem.  But if we didn’t address the underlying humidity problem, we’d still leave the client with conditions highly conducive to dust mites and other allergens.  Other IAQ issues, such as elevated contaminants are typically present with elevated humidity as well.  The solution?  Address the underlying humidity and ventilation issues and we not only address the mold problem, but also dust mites, odor buildup, VOC problems, etc.

Mold inhibitor with mold growth.

What about future moisture issues?  Good question!  Mold preventative coatings are often marketed as the solution to unknown moisture issues that may strike in the years to come.  A plumbing leak?  No problem.  The XYZ mold inhibitor will stop mold growth before it starts.  This sounds great in theory, but quickly falls apart in actual building environments.


The problem is due to a settled dust.  Any surface, whether vertical or even inverted, quickly accumulates a thin layer of settled dust.  This settled dust is comprised of many types of particulates, but a significant amount comes from human skin, pet dander and other organic compounds. These unfortunately provide a perfect food sources for mold growth.

Now apply this to a mold prevention coating.  A contractor applies the coating throughout the home.  For a few weeks, no mold growth is possible, as the mold inhibitor does its job.  However, within a short while, a thin layer of dust settles on the surface.  As mentioned before, this deposit of dust is a perfect food source for mold, and thus quickly renders even the most powerful coating absolutely useless.

Failure of a mold prevention coating

Herein lies the caveat.  Mold prevention coatings can be useful if you only need to buy yourself a few week’s time.  For example, if you’re framing a house in the winter and saturation is inevitable, a mold inhibitor coating can prevent mold growth while the building is dried out.  In every other circumstance, a mold prevention coating is worth very little.

Need a bit more proof?  Below is a photo of heavy mold growth on a nylon backpack.  Nylon, of course, is not a food source for mold growth.  Yet mold had no problem attacking the layer of dust and debris found on the surface.

Example of why mold inhibitors won't work.







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