Roy – all good info but my
Roy – all good info but my point still stands: if you (the average homeowner) are not constantly measuring what constitutes good (or bad) IAQ you really don’t know if you have a problem, nor what the real problem might be, nor if you solved the problem after you implement a solution. And the average homeowner will not implement a high-cost measurement device. So any deployed “one-size-fits-all” solutions are just not-real-educated guesswork.

David, the chart on that
David, the chart on that website has been modified by the manufacturer to suit their purposes. If you go to ASHRAE Std. 52.2 where MERV is officially defined, it shows that MERV 8 filters must have a particle removal efficiency of at least 20% for particles in the 1 to 3 micron range. That’s not a very high efficiency, but it will remove some PM2.5. Filters in the MERV 13-16 are not HEPA range. MERV 16 filters have removal efficiencies of 95% or more for particles from 0.3 to 10 microns, but HEPA filters must have a particle removal efficiency of 99.97% or above for particle larger than 0.3 microns. There is no MERV equivalent for HEPA performance, in fact, those are two different rating systems. As far as MERV 13+ filters “negatively affecting” equipment, I see no basis for that unless they are assuming that the pressure drop is higher and will thus reduce airflow rates in the system. However, filter pressure drop is not inherently related to the MERV value, in fact, I have seen higher MERV rated filters with lower pressure drops. It just depends on the overall filter design. Apparently, this company does not have high MERV filters with reasonable pressure drops available.

From what I see, only MERV 11
From what I see, only MERV 11 and greater filters work for PM2.5, See the chart here: http://www.ontimeairfilters.com/air-filter-merv-rating. Notice that MERV 13+ filters (HEPA range) are used at filtering bacteria, tobacco smoke and sneeze contaminates but this firm doesn’t recommend them for HVAC systems as it may negatively affect them (i.e., they’re not made to really clean the air, just “sorta clean” the air).

You don’t need a HEPA filter
You don’t need a HEPA filter to removed PM2.5. HEPA filters are for particle sizes down to 0.3 microns and are overkill for PM2.5. For 2.5 micron particles, you need MERV 8 or higher.

See the next installment of
See the next installment of Allison’s blog for more discussion on “What is bad”. Also see what the US EPA considers in their (outdoor) Air Quality Index: https://airnow.gov/index.cfm?action=aqibasics.aqi.

I think the $269 for a
I think the $269 for a monitor that does not monitor any particulate material (of any size)m ozone or CO is a non-starter; too costly, doesn’t measure enough “stuff”, doesn’t set off any mitigation devices. I have a very good digital temp/relative humidity gauge I got off Amazon for $8. If it isn’t under $100 it will not be accepted by the main market. If it doesn’t start up some kind of remediation device or at least set off an alarm it is not providing much value.
Nate Adams (Ohio) had a very good review a couple years ago of a number of devices with an interesting testing methodology: http://energysmartohio.com/indoor-air-quality/which-indoor-air-quality-monitors-are-best-and-why/
The other side of this “coin” is what do you do about it? My understanding is that the only real device that removes PM2.5 is a HEPA filter so your IAQ system would need one of these at every air return port. How many HVAC/ERV/HRV systems have just 1 HEPA filter (let alone 1 for each return port)? How many home owners replace them each month (this is where the monitoring device comes in)?

Yes, those are good points.
Yes, those are good points. Since I have spent the last 40 years in offices, I forget about the previous 20 as a kid and the next 20 as a possible retiree. This shows how averages can lead to confusion about real individual cases.

In addition to a lot of work
In addition to a lot of work being performed outside an office or a factory, if you look at let’s say 80 years of life, most people only work around 43 years (e.g. from 22 to 65) which is 53 % of their time. So that 23 % would based on that alone drop to around 12 % for somebody that holds an office job for 43 years. Plus usually in those type of jobs after years you have more than 2 weeks of vacation, sick time, holidays, maybe periods of unemployment, etc. … so I can see how the number will shrink even further based on that.

You also have to count
You also have to count children and retirees. For the first 20 years, and the last 0-50 years (depending on retirement age and lifespan), we’re inside a lot without being at work. And we also (always) miscount stay-at-home parents who are “at work” 24 hours a day, but are probably counted in the study as “at home”. Together, these groups could certainly bring down that 23% number by quite a bit.