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1. Tl;dr

Many reports indicate that indoor air quality (IAQ) interventions are likely to be effective at reducing respiratory disease transmission. However, to date there’s been very little focus on the workforce that will implement these interventions. I suggest that the US Heating, Ventilation and Air Conditioning (HVAC) and building maintenance workforces have already posed a significant obstacle to these interventions, and broad uptake of IAQ measures will be significantly hindered by them in the future. The impact will vary in predictable ways depending on the nature of the intervention and its implementation. We should favor simple techniques with improved oversight and outsource or crosscheck technically complex work to people outside of the current HVAC workforce. We should also make IAQ conditions and devices as transparent as possible to both experts and building occupants.

To skip my bio and the technical horrors section, proceed to the recommendations in section 4.

2. Who am I? Why do I think This? How Certain am I? 

I began working in construction in 1991. I did a formal carpentry apprenticeship in Victoria BC in the mid-90s and moved to the US in ‘99. Around 2008 I started taking greater interest in HVAC because - despite paying top dollar to local subcontractors - our projects had persistent HVAC problems. Despite protestations that they were following exemplary practices, our projects were plagued with high humidity, loud noise, frequent mechanical failure, and room-to-room temperature differences. This led me to first learn all aspects of system design and controls, and culminated in full system installations. Along the way I obtained a NJ Master HVAC license, performed the thermal work of ~2k light-duty energy retrofits, obtained multiple certifications in HVAC and low-energy design, and became a regional expert in building diagnostics. Since 2010 I’ve worked as a contractor or consultant to roughly a dozen major HVAC contractors and hundreds of homeowners.

I’m reasonably certain that the baseline competence of the HVAC workforce is insufficient to broadly and reliably deploy IAQ interventions and that this is a serious obstacle. My comments are specific to the US. I’ve discussed these problems extensively with friends and acquaintances working at a national level and in other parts of the US and believe them to be common to most of the country. The problems are specific to the light commercial and residential workforce, but not domains that are closely monitored by mechanical engineering teams (e.g. hospitals). Based on some limited experience I suspect these problems are also common to Canada, but I’m less certain about their severity.

3. Technical Horrors: Why is This so Difficult?

Within HVAC, many important jobs are currently either not performed or delegated to people who are largely incapable of performing them. Many people convincingly lie about their capacity to perform a job they’re incapable of, report having done things they haven’t, or even make statements at odds with physics.

Examples include:

  • Accurate heat load/loss calculations: These are used to size heating and cooling systems, and in most areas are code mandated for both new and replacement systems. Competent sizing (Manual J for residential) is viewed as highly important by virtually all experts within HVAC. However, despite decades of investment in training and compliance, a lead technical manager of a clean energy program reported to me that >90% of Manual Js reviewed by his program had significant errors made apparent due to internal inconsistency (eg duct load on a hydronic system) or obvious inconsistencies with public information on zillow or google maps. In an especially egregious example, one of the largest HVAC companies in the state had its Manual J submission admin go on vacation. The temporary replacement forgot to rename files and submitted applications named for their installed capacity (1 ton, 2 ton, 3 ton, etc.), revealing that the company had submitted copies of the same handful of designs for thousands of homes.
  • Setting and correcting airflow: In systems equipped with a furnace and air conditioner this is especially common. The furnace fan motor moves air for both heating and cooling. However, most furnace fans are capable of moving a range of airflow for various capacities of air conditioning (a 5 ton furnace fan may have 3-5 tons of airflow capacity), and therefore must be programmed. The great majority of these are not programmed, leaving the fan in a default setting, which is usually its highest nominal airflow. In most cases this is too high. The net effect is a significant loss of dehumidification in a sizable number of homes and excessive system noise. Almost all of my “very humid home” diagnostic calls have this condition, often with multiple HVAC techs failing to detect the problem prior to my visit in spite of obvious symptoms (little to no condensate being produced by the AC system).
  • During the early phases of the Covid-19 pandemic, public health officials asked school managers across the country to upgrade their central ducted HVAC system filters to MERV 13 and set the fans to continuous circulation. However, a sizable number of building managers reported that these systems, “couldn’t handle the pressure of a filter upgrade.” This statement was largely taken at face value by public health officials and parents, despite the great majority of cases being 1) corroborating information via equipment manuals not being provided in any case I’m aware of, and 2) not based on (total external static) pressure (TESP) readings taken from equipment in any case I’m aware of. In the vast majority cases the people making this claim didn’t even possess the tools or knowledge to measure TESP. In evaluating this claim in person and remotely several times, I have yet to find a claim backed by data, suggesting the default position should be that the claim is false.
  • In the mid-90s John Proctor created CheckMe as a tool to evaluate the rampant false claims of technicians charging refrigerant. Data collected by Proctor on 8,873 systems suggested that 65% were in need of repair adjustment to charge. These repairs largely wouldn’t have been discovered in the absence of the CheckMe tool. 
  • Electrification in response to global warming has rightly gained significant policy traction. However, electrification will necessitate widespread heat pump adoption in cold climates, most of which currently require the field installation and verification of refrigerant charge. The most common residential equipment refrigerant today is R410a, which has a somewhat high global warming potential (GWP 2088). Procedures for the installation of “tight & dry” systems are contained in equipment manuals and broadly disseminated by industry field guides & standards. In principle, adhering to these installation standards makes near-term failure exceedingly rare. However, despite widespread access to these standards many of the gains of electrification are being clawed back by unexpectedly high refrigerant leak rates, primarily due to a systematic failure of the HVAC labor force to follow best practices.

HVAC competence is a strong determinant of IAQ intervention success. Surprisingly, public health experts have largely avoided examining the labor force presumably tasked with performing most of their proposed interventions. In part I suspect this is due to differences in their respective cultures, tasks performed within them, and some intrinsic differences between white and blue collar work.

Public health work is similar to most knowledge work wherein ‘doing’ is physically minimally distinct from ‘researching’, ‘proposing’ or ‘planning’. With physical work, talking or writing is much easier than doing. In addition, white collar work is often characterized by higher levels of transparency, and dishonesty is frowned upon and frequently held to account. None of these are true of HVAC work, where honesty isn’t a strong cultural norm, and many tasks lack sufficient transparency to allow for its policing.

4. Recommendations

For many years, poor competence has resulted in suboptimal outcomes for the occupants of many buildings. For example, at the beginning of the Covid-19 pandemic many teachers had endured years of seemingly intractable comfort problems despite many failed repair attempts. Once the pandemic struck, these teachers understood that the ventilation and filtration provided by the same technicians had inherently lower verifiability than previous HVAC work. Naturally they were hesitant to entrust occupant health to the same people who had frequently failed them. Therefore, the success of future IAQ interventions significantly depends on providing clear and verifiable information to building occupants.

Interventions That are Likely to Fail

Complexity and opacity strongly predict failure. Tasks involving direct airflow measurement or its longstanding proxies (temperature and pressure) are especially problematic, as these aren’t well understood. Most technicians won’t have the knowledge or tools to quantify airflow. Keep in mind that technicians and managers routinely lie, so asking whether an individual or company can perform a task has the potential to select for lying instead of competence.

Suppose we wanted to invent a seemingly viable yet pragmatically horrible device that exploited the worst industry traits. We’d probably create something like in-duct UV that’s dependent on a narrow range of airflow velocity, installed in a system capable of providing too much/too little airflow for the device to be effective. We’d add the possibility that the device could be installed in multiple configurations (backwards or upside-down) or multiple locations (supply or return plenums or trunks) with performance and safety impacts from each. Finally, we’d add the condition that the device wouldn’t convey its sub-optimal performance to installers or end-users. While there may be some other conditions we could add to make this worse, we’ve probably created a device that’s virtually guaranteed not to work effectively, while simultaneously providing naive building occupants with the illusion of increased safety. Interestingly, current public health understanding of HVAC industry capacity would find little fault with this device provided its installation in optimal conditions produced favorable results.

Interventions That are Likely to Succeed

The ideal intervention requires minimal technical sophistication, and its proper functioning is both comprehensible and visible, ideally even to occupants. Where necessary, expert planning should be performed by people with minimal connections to the HVAC industry. Many current interventions are broadly promising, but leave significant room for improvement. Given the limitations proposed herein, I suggest the following:

  • Displayed CO2 as proxy: Carbon dioxide is a good proxy for indoor air quality generally, and respiratory virus transmission risk specifically. While handheld CO2 monitors have become somewhat widespread, to date visible public displays have gained very little traction. In part this is due to the complexity of clear targets for rooms in which mixed ventilation and filtration are both present. However, this could probably be addressed via multiple targets in rooms with standalone filters with known Clean Air Delivery Rate (CADR).
  • Displayed Clean Air Delivery Rate (CADR) on visible, standalone filters. Standalone filters are superior to central ones because laypeople aren’t readily able to verify central system filtration rates. However, with improvements to the display of CADR on freestanding filters, it would be fairly simple for a sophisticated layperson to roughly calculate the filtered air exchanges in a given room. 
  • Adopt standards for UV air exchanges and display them: UV is a highly promising intervention for reducing disease transmission. We’ve already established that in-duct UV has a strong potential for failure. However, unlike filtration and ventilation, UV currently lacks an agreed upon standard of work rate. Consequently, current freestanding versions of the technology lack visible displays showing effective operation. 
  • Improve the transparency of necessary HVAC work: Where HVAC service or installation is required, transparency should be the default position. Technicians should geotag pics of measured performance and diagnostics. Claims regarding equipment parameters and limitations should include geotagged photos of nameplates and highlighted sections from installation manuals (most manuals are accessible via web search currently).
  • Improve transparency of ventilation calculations: Most ventilation calculations (including ASHRAE 62.1 & 62.2) are moderately simple to perform and unconnected to the routine demands of HVAC work. Our default position should be to have these calculations at minimum available, - and ideally cross-checked - by interested laypeople.

The HVAC and building maintenance workforces are significant obstacles to widespread IAQ improvements. However, to accept the limitations I’ve outlined isn’t to accept failure. Historic failures provide us with a blueprint for success provided we use them to guide our future actions.


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Sorted by Click to highlight new comments since: Today at 12:31 AM

I appreciate this post, thanks for sharing it! I'm curating it. I should flag that I haven't properly dug into it (curating after a quick read), and don't have any expertise in this. 

Another flag is that I would love to see more links for parts of this post like the following: "In an especially egregious example, one of the largest HVAC companies in the state had its Manual J submission admin go on vacation. The temporary replacement forgot to rename files and submitted applications named for their installed capacity (1 ton, 2 ton, 3 ton, etc.), revealing that the company had submitted copies of the same handful of designs for thousands of homes." I don't fully understand what happened or why (the company was cutting corners and was pretending the designs were customized when they were actually not?), and a link would help me learn more (and see if I agree with your use of this example!). (Same with the example about building managers in schools in the early days of COVID.)

I'm really grateful that you've shared this; I think the topic is relevant, and I'd be excited to see more experts sharing their experiences and what various proposals might be missing. I particularly appreciated that you shared a bit about your background, that you used a lot of examples, and that the "Complexity and opacity strongly predict failure" heuristic is clear and makes sense. I think further work here would be great! I'd be particularly excited about something like a lit review on many of the interventions you listed as promising (which would also help collect more readings), and estimates for their potential costs and impacts. 

Minor suggestion/question: would you mind if I made the headings in your post into actual headings? Then they'd show up in the table of contents on the side, and we could link to them. (E.g.)

Thanks! I'm not totally clear on what curate means in this context but am definitely amenable to editing for clarity!

Those are very valid criticisms. Before posting I felt there were two major shortcomings. 1) It's argumentative (vs scout mindset), and  2) the claims aren't well verified. Taking a different approach with 1) felt disingenuous, but 2) remains problematic.

I'm not aware of any quality empirical work directly focusing on the shortcomings of this workforce. I think this is partly due to a significant disconnect between people working in public health and people working in the industry. So when public health people encounter this argument they say something like "yes we'll need more training for technicians" which isn't really the claim I'm making (an important person from a PH thinktank actually just did this in response to this post lol). I'll try to better corroborate the claims or come up with more readily documented ones. Ultimately I think we'll still be left with something tantamount to a firehouse of anecdotes, which readers will have to decide whether or not to take at face value.

I can definitely better explain Manual J. I'll also give some thought to illustrating the school building manager point more effectively. 

Feel free to edit the headings however you see fit. I'll look for that feature if I make any future posts.

Is it OK if I share the original draft with you? Thanks!

It's hard to think of an industry that has a larger gap between best practice and what is typical than HVAC. Thanks for highlighting this.

Exactly! I'm not making observations that people in the industry aren't aware of. On the other hand, I've yet to see any sort of acknowledgement that this might feature in disease reduction decision-making. It's made the last 3 years a bit surreal, tbh.

I was speaking with someone working on far-UVC research who mentioned that one of the biggest obstacles to GUV being implemented despite it being around for ages is the lack of skilled technicians to install them (which is what we included in our Resources Portal page on how engineers can contribute to biosecurity). I didn't realise the nuances of this until I read this post – so I really appreciate your work here!

Seems right! I think some of the biggest opportunities are improvements to technology that anticipate and correct for downstream failure. To some extent sophisticated manufacturers already do this - eg constant airflow fans installed in restrictive duct systems tend to fail prematurely. Many of Mitsubishi's air handlers now limit external static pressure to .8 inches of water column, I suspect in response to these high failure rates.

ctrl f "external static pressure"


Thanks Jesse, wish we had more like this on the forum! I really appreciate being able to see more clearly what the obstacles between what seem like the most effective set of solutions and their actual implementations are, and how to overcome them.

Thanks Rachel!

Really interesting post! Some ideas:

  • It seems like a lot of the problems around dishonesty are facilitated by having the same organization responsible for determining what the situation requires, installing it, and verifying that it is installed correctly and/or performing adequately. Could we pull these apart into separate entities? For example, when we had hazardous material remediation on our house the verification was a completely separate organization.

  • With UV it seems like a big part of the problem is that it's hard to tell if the system as installed is doing what it should. With fresh air you can check CO2 levels, but there isn't something similar for UV. I wonder if it would be possible to develop a cheap test for this, that could be performed as part of standard acceptance testing for a new system? And ideally repeated on stove schedule? Perhaps something like finding a gas that changes into a different one when exposed to UV, releasing it into the building, and then monitoring levels of both that gas and the one UV modifies it to?

  • This seems like it pushes for upper room UV over in-duct UV, because in the former case you can check that it's installed properly pretty easily: verify that UV levels are sufficiently low at head height and sufficiently high above that. Sometimes the need for testing that lower room UV levels are sufficiently low is described as a downside for upper room UV, but maybe it isn't if you actually need testing regardless and testing is more likely to happen and be done correctly in the upper room case.


Re 1) This is probably a factor, but I'd guess it would have low tractability and even if completely corrected would have limited impact. This was the basis for CheckMe that I mention in the post, and since then there are many technological innovations that make crosschecking really simple but have limited impact. For instance, if properly implemented, digital instruments integrated into platforms like measure quick would fix a ton of problems, but I don't see much happening irl with this. 

2) Exactly! Not sure on test, but operating within parameters doesn't seem like a crazy ask.

3) Yes, that's definitely on of the points I was trying to make. If we're choosing between systems that have the theoretical capacity to work in a highly optimized way but are failure-prone and opaque vs systems that work sub-optimally but are readily verified and less failure-prone then I think we should choose the latter.

Thanks so much for writing this; super interesting and important.

Your post also highlights to me the importance of having EAs with a wide range of backgrounds and experiences. For instance, the overwhelming majority of EAs have white collar jobs, so I suspect a lot of us didn’t know/wouldn’t have guessed this:

“White collar work is often characterized by higher levels of transparency, and dishonesty is frowned upon and frequently held to account. None of these are true of HVAC work, where honesty isn’t a strong cultural norm, and many tasks lack sufficient transparency to allow for its policing.”

Thanks! Tbh I was pretty close to cutting that part due to superfluity so I'm happy to hear you found it insightful. 

I agree that there are potential areas where drawing from a wide range of backgrounds could be better than the current structure. Tbc, I don't want to overrate this and it's likely highly domain specific. Long before this I started a piece on the widespread conflation of physical skills vs knowledge that characterizes much of the collapse recovery focus. This also also seems like a potential white collar silo phenomenon.

This is really great - thanks for writing this.

Thanks! Glad you like it!

This is a really interesting post! I think we need more posts like this that detail the practical obstacles to the implementation of solutions. Have shared with the High Impact Engineers Slack!

Thanks! I just signed up. Very curious to see if this is a feature of other technical areas.

Hello Jesse! Great article. I felt the need to translate the article into Spanish to make it accessible for Spanish-speaking individuals! That being said, I'm from Florida, where my home has perennially battled with high humidity. Since childhood, I've dealt with allergies and frequent respiratory illnesses and even saw my mother develop rhinitis. We were under the impression that our HVAC system was functioning optimally, but after reviewing this article, I've come to understand that there's considerable scope for improvement and proactive maintenance. As you mentioned, the workforce isn't very instructed on what to do or has the best interests in installing a safe and reliable system. Thanks again for this. I learned a lot and will put it to use. 

Thanks so much for doing that! 

Florida is a challenging environment. Right-sizing (manual J) of cooling equipment is especially important in humid climates. In over-sized systems, short run times tend to satisfy the thermostat but not properly dehumidify, because this takes much longer. In addition, Florida has many duct systems in unconditioned attics, and duct leakage draws humid air and contaminants from outdoors. If you have a system in an unconditioned attic this should be at minimum fastidiously sealed. Many people in building geek circles feel that conditioned attics are warranted, but my experience suggests that these aren't often cost-effective retrofits: https://buildingscience.com/documents/building-science-insights-newsletters/bsi-119-conditioned-unconditioned

The final 2 considerations are 1) turning the AC fan to the lowest possible speed that can be sustained without freezing the indoor coil. This is generally ~325 cubic feet/minute per nominal ton of cooling. And 2) adding supplemental dehumidification. Target <55% relative humidity at ~75F. This can be a simple standalone dehumidifier piped directly to a sump or condensate pump.

For filtration, recommendations largely in line with pandemic seem fine for small particulate too - i.e. MERV 13 filters in centralized systems. IAQ monitors can be great tools as well!

Reach out directly if you need anything!

great educational article, thanks!