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.