When most people see the 'AC' in HVAC they think comfort cooling when in fact they should see conditioning of air or 'CA' since the original intent in HVAC included deodorization, de(humidification), and decontamination. In fact 'CA' is appropriately the most suitable surrogate for the H and V in HVAC that we should just all together bury the HVAC acronym.

The confusion over HVAC and IAQ was evident in what I witnessed in the filter aisle at a well-known Canadian retailer. From this impromptu retail survey I discovered that next to money, sex, vacations and kids, a significant amount of marital discord revolves around how much to spend on what model of furnace air filter. Have you ever seen what happens when two educated but completely ill informed people stand arguing in public in front of rows of filters with meaningless (to them) descriptions? The folks I observed were not there because they cared about protecting their furnace – they were there because of the quality of air in their home.

My hunch is that not one person in the purchasing department at corporate retail right on down to the dazed teenage store clerk have been educated on indoor air quality and the air filters stocked on their shelves. Even if combative consumers resolve to buy the best of the bunch based entirely on price, in all likelihood it is still a furnace filter. It will do nothing but protect the furnace – hence the most brilliant and appropriate term 'furnace filter'.

As consumers we're often naive about things that matter most. In this case most consumers think furnace filter means indoor air quality filter. It is one of those unfortunate byproducts from thinking 'AC' means cooling.

This retail roulette with HVAC filters happens across North America on an hourly basis despite housing studies¹ associating asthma and bronchial responsiveness with ducted heating and air conditioning systems.² Further, it may come as a surprise to readers that at the time of writing this article, a specific IAQ filtration specification remains absent from Canada's F326 Residential Mechanical Ventilation Systems Standard (assumed to address IAQ) so if adequate filtration is not specified in the nation’s ventilation standard what do you think the odds are for the general public roaming the retail aisle to pick a suitable model when left to their own accord? It is slim in my books since consumers and industry alike also see furnace filters as a type of strainer like some kitchen tool but with added super powers against odors and gases such as ozone and radon.

Air filters are not particle strainers – they are gauntlets and the ability of a filter to create easy or difficult passage through the gauntlet is based on several mechanisms addressing various air borne particulate characteristics including aerodynamic diameters, size, density, and concentrations. So it should not come as any surprise that particulate filters are not designed to address anything but particulate thus the reason they are called particle filters and not gas or odor filters – go figure.

Filtration mechanisms at work - filters are gauntlets not strainers
 

Testing for particle filters is voluntary and ratings for inline duct mounted filters for whole-building filtration can be tested to the American Society of Heating, Refrigerating, and Air-Conditioning Engineers ANSI/ASHRAE Standard 52.2-2007, Method of Testing General Ventilation Air- Cleaning Devices for Removal Efficiency by Particle Size - for what is known as a MERV designation.

MERV is the acronym for "minimum efficiency reporting value." The test is done with a soufflé of particles with various characteristics measured in sizes ranging from 0.30 to 10.0 microns, which are measured using sophisticated particle counters and recorded as a differential between the up and down stream sides on the filter. The primary scale goes from 1 to 16 with HEPA and ULPA topping the scale off between 17 and 20. Most so called 'furnace filters' on a good day might have a MERV 4 rating; MERV 8 is minimum for 'healthy home' principles and to have a MERV 12 rating, a filter must be at least 80 per cent efficiency for particles in the 1.0- to 3.0 micron size range and 90 per cent or better in the 3.0- to 10.0 micron range.³

So how big is a micron? Well, a human hair is roughly 60 microns, the allergens your dog distributes on your kid’s bed are about 7 microns and viruses are between 0.1 to 1.0 microns. The particles that are of concern to health professionals are called PM₁₀ indicating particulate matter less than 10 microns. This includes pollen, bacteria and mould spores. These airborne particulate are respirable meaning they can enter our respiratory systems.

In the grouping of PM₁₀ is PM_1.0, which can work their way into the deep part of our lungs where oxygen exchanges with carbon dioxide in the blood through the ultra thin membrane of the alveoli.

Let's be clear about particulate filters.

Particulate filters reduce the airborne particulate and improve the quality of air, but it is beyond the skills of the mechanical industry to state that air filters improve the quality of one's health, even if consumers want to hear it. Only a healthcare professional, such as an allergist, could make such a statement and even if they did it would be based on case studies often lasting a number of years.⁴ Additionally, the results reported would only apply to those studied with the caveat that outcomes should not be extrapolated and applied to the general population. Unless we are licensed medical practitioners we would be best advised to avoid making statements about people's health and air filters. We should focus on the actual outcome of filtration, which is to reduce airborne particulate matter (PM).

Finally, we should also be doing a better job as an industry pointing out that a nickel a day ($20 per filter/year) is fine if you want to ensure the furnace is filtered but completely inadequate if indoor air quality particulate is a concern.

Our base recommendation for the average Jill and Jack is a MERV 9-12 filter for particulate and an optional activated carbon based filter for some common household gases.