Analyzing a database of over 6 million online sales of residential HVAC filters from 2008 to 2017

Back in May 2018 I was invited to give a talk about our research on mass-based HVAC particle filtration metrics at the National Air Filtration Association’s (NAFA) annual Tech Seminar, and I made a pitch to the audience of mostly filter manufacturers and retailers that the academic community needs more information on the residential air filtration market. Basically: how can we estimate what fraction of the U.S. population uses what kinds of filters? I’ve tried to get at this question before. In a 2014 paper in which we needed some statistics on the national distribution of filter ownership, we really had to make some back of the envelope estimates from a variety of fairly low quality sources (including some personal communication with a colleague in the industry who gave us the thumbs up on our estimates, saying “that sounds about right”).

Fortunately, one of the audience members at my NAFA Tech Seminar presentation, Rich Scott from Discount Filters, a major online retailer of HVAC filters, volunteered to provide me some sales data. Rich and his team provided me a database of over 6 million filters they have sold to (mostly) residential customers from 2008 to 2017. I say “mostly” because they sorted the data by commercial vs. residential address, although they know that not to be the most accurate description of their customers, but sufficient enough for this purpose. There are a few other caveats worth noting about their data as well, including: 1) the sample is large, but might not represent the entire U.S. residential marketplace (e.g., online consumers might differ from in-store consumers; some of their customers are large management organizations that buy lots of filters, which can dwarf individual consumers); 2) they don’t sell every type of filter under the sun, so the data are obviously skewed to the products they sell (e.g., they only sell MERV filters and not other metrics like FPR or MPR; these are mostly 1-inch filters and deeper-bed 4- and 5-inch filters combined into one data set, I don’t think there are any 2″ filters here); and 3) some of the trends over time capture more than just changes in sales due to consumer preference alone (e.g. changes are also affected by the marketing efforts and product offerings of this particular retailer, which have also changed over time). Nevertheless, let’s look at the data! Many thanks to Rich Scott and Tyler Dishman at Discount Filters for providing these data and being so willing to share the data publicly. 

First, let’s look at the data set of sales over time. Their sales grew from ~180,000 filters in 2008 to ~1.3 million filters in 2017. The total number of filters in the data set is about 6.4 million from 2008 to 2017.

Total number of (mostly) residential filters sold by discountfilters.com from 2008 to 2017

That’s a lot of filters! Next, let’s look at the trends of fraction of total sales of the different filter types that this retailer sells over the same time period. 

Fraction of different types of (mostly) residential filters sold by discountfilters.com from 2008 to 2017

You can see MERV 13 steadily on the rise since 2008, while the fraction of MERV 8, 11, and fiberglass (i.e. low MERV, probably less than MERV 4) filters are all fairly steady over time, albeit with some year to year variation. MERV 10 filters have been decreasing but the retailer mentioned to me that has less to do with the filters themselves and more to do with production and marketing (in other words, the retailer has moved away from MERV 10 in favor of some of the other filters). Washable, MERV 16, and activated carbon filter sales were steadily low throughout the period.

Last, let’s look at a snapshot of these same data in 2017, the most recent full year of sales in the data set. 

Fraction of different types of (mostly) residential filters sold by discountfilters.com in 2017

In 2017, for this particular retailer, MERV 11 filters made up the largest share of sales at about 35%, followed by MERV 8 at about 29% of sales. Fiberglass filters were third at around 16% followed by MERV 13 filters at about 14% of sales. In fact, fewer than 15% of filters sold were MERV 13 or higher. These data suggest that at least for shoppers on this major online retail site, not that many people are using high efficiency filters in U.S. residences! I hope you find these data helpful.




BERG provides comments on proposed 2019 California Title 24 residential air filtration requirements

California’s Title 24 of the CA Code of Regulations — also known as the California Energy Code or part 6 of the CA Building Standards Code — is one of the most (if not the most) aggressive codes in the country in terms of advancing energy efficiency in buildings. It was created in 1978 by the CA Building Standards Commission in response to a legislative mandate to reduce CA’s energy consumption. It undergoes periodic revision and has continued to strength its efficiency standards over time, setting the pace for the rest of the country.

Most items in the code deal explicitly with energy efficiency, but in recent years more language has been adopted to promote better indoor environmental quality. We were recently asked to provide our opinion on some new proposed language regarding air filtration for the upcoming (2019) rulemaking process. Since this is an in which we are active, BERG PhD student Torkan Fazli and I decided to provide a brief opinion.

Among the changes proposed to Title 24 in 2019 is language to increase the level of air filtration required for new residential construction, from MERV 6 to MERV 13, with the stated goal of reducing indoor PM2.5 concentrations. This is quite a bold move in a relatively slow-to-change industry. To accommodate the higher efficiency filter requirements, the proposed changes would also require that return grilles be able to accommodate at least a 2-inch deep filter to ensure that MERV 13 filters can be installed with minimal impact on HVAC system performance. You can read more about the justification for the proposed changes at the Title 24 residential indoor air quality and ventilation stakeholders site.

This is an area that I’ve done a lot of work in, starting with my master’s thesis work under Dr. Jeff Siegel then at the University of Texas (here and here), and more recently at Illinois Tech working with several graduate students (e.g. here, here, and here). Even more recently, we’ve been conducting measurements of filter pressure drop, air handler flow rates (in a nominal 1000 CFM air handler with a PSC blower), and in-situ filtration efficiency for fine and ultrafine particles for a large number of commercially available filters with various manufacturer-reported ratings (e.g., MERV = minimum efficiency reporting value, FPR = filter performance rating, and MPR = micro-particle performance rating) and various depths (e.g., 1-inch, 2-inch, 4-inch, and 5-inch). You can read about some of this initial testing here. We’ve now tested about 50 filters, 36 of which have had a MERV rating reported by the manufacturer. We plan to publish this work in the near future, but until then, we provided some our data on pressure drop and MERV to help justify the proposed Title 24 changes. The figure below shows filter pressure drop measurements made with each of these 36 filters plotted against the manufacturer-reported MERV rating for each filter. Note that all pressure drops are measured with new (clean) filters.

Filter pressure drop versus MERV # for various depth new (clean) filters

From this work, our previous work, and the work of several others referenced throughout the publications linked above, I think we can generally conclude the following about higher efficiency residential filters:

  • PM2.5 is probably the most important indoor pollutant to control to mitigate long-term (chronic) adverse health outcomes associated with indoor pollutant exposure
  • Only MERV 13 filters and above are explicitly required to have a single pass removal efficiency of at least 50% for particles smaller than 1 µm (according to ASHRAE Standard 52.2)
  • Targeting removal of particles 0.3-1 µm generally increases PM2.5 removal efficiency, more so than targeting removal of 1-3 µm or 3-10 µm particles
  • Therefore, MERV 13 makes sense from a public health perspective
  • MERV 13 filters can have high pressure drops, particularly in the narrower 1-inch depth variety
  • The energy consequences of high filter pressure drops are probably smaller than most people think, but they can still cause increased fan energy consumption in residential systems with ECM fan motors that increase fan power to maintain the same airflow rate and can cause longer system runtimes (and thus higher energy consumption) in residential systems with PSC fan motors that respond to increased pressure drop by reducing air handler flow rates and thus capacity
  • Thicker depth filters — including at minimum 2-inch filters — tend to have lower pressure drops than 1-inch filters within a given MERV category
  • Therefore, if one is to move to MERV 13, one should strive to accommodate deeper bed filters that should have fewer pressure drop issues

For these reasons, we generally support the move to require MERV 13 and minimum 2-inch depth filters. You can read our full statement here, as recorded in the California Energy Commission docket log.




Some thoughts on conducting energy and environmental research during the first 2 months of the Trump administration

I don’t think of Twitter threads as a particularly helpful means of communication, but it’s a good way to rant about my experience conducting energy and environmental research during the first 2 months of the Trump administration:

Thanks to Chuck Haas at Drexel University as well for making a Storify of this thread.




New 3D printer test: Up Box+ Printer with HEPA filter

We recently tested emissions of ultrafine particles (UFPs) and spectated volatile organic compounds (VOCs) from an Up Box+ desktop 3D printer using ABS filament, which is a relatively unique product on the market because it includes a 100% recirculating HEPA filter inside a full enclosure in order to reduce particle emissions. It’s one of the first, if not the first, printer that we’ve seen specifically address UFP emissions. (However, we should also note that it does not have any intentional gas phase filtration to reduce VOC emissions). Results of our tests are provided in detail in the full report, but briefly:

  • The total number of UFPs emitted throughout the test print job was reduced by about 74% simply by printing with the enclosure completely closed (but no filter operating) compared to operating the printer with an open enclosure
  • The total number of UFPs emitted throughout the test print job was reduced by about 91% by printing with the enclosure closed and HEPA filtration system switched on compared to operating the printer with an open enclosure
  • VOC emissions were relatively low compared to other printers and filaments we’ve tested, although surprisingly, operating the printer with the enclosure closed (but without the filter operating) actually increased VOC emission rates by about 50%, while operating the printer with the enclosure closed and with the HEPA filtration system switched on decreased VOC emission rates by about 20%. However, both of these values are near the estimated uncertainty in our measurement and we didn’t get a chance to perform replicate testing, so it’s not clear how meaningful the VOC results really are



New batch of 3D printer filament emissions tests available

We have released 7 new reports on ultrafine particle (UFP) and volatile organic compound (VOC) emissions tests conducted in our lab in 2016 using a Lulzbot Mini 3D printer and 7 different commercially available filaments. Scroll down to the bottom of our 3d printer emissions testing page to see the reports, or download them below: