Air conditioning systems - simple, cheap, coronavirus mitigation

Checkout this article regarding coronavirus spread through building air conditioning systems, and how to simply and cheaply mitigate it:

Article from an NZ national engineering consultant:

Basically, all management have to do is leave the aircon fans on overnight, and purge the air in the building. This does not cost that much - it is heating and cooling that costs a lot.

Also – news article:
“Coronavirus could be spread by air-conditioning and may be more contagious than previously thought, scientists believe after finding traces of the virus in hospital air-duct”

Governments are spending $trillions on coronavirus mitigation measures, and we don’t hear a word about this simple, cheap mitigation measure that could be implemented immediately with the flick of a switch.

I worked in CBD office towers for 40 years. I did a lot of after hours work - every building sets the aircon to turn off automatically at about 6pm and back on at 7am, and take a week to change 100% of the air in a building (about 15%/day). I used to get multiple colds and flu’s every year. Now that I am retired, I don’t get anywhere near as many. Workers have to live with this life-long affliction … and now die of coronavirus … just so management can save a few pennies on aircon electricity

Hi @Paradox, welcome to the community.

As a first post, this is interesting information however, there seems little available scientific evidence of the claims made by the air-conditioning servicing expert.

It is also worth noting that similar information from the same expert/company appears elsewhere on the internet.

I wonder if this information is about self promotion or creating an issue to drive more business.

One has to take care when reading information on the internet, especially those which commercial interests as the agenda may not be what it initially appears.

If you or anyone have/has any information from agencies such as WHO, US Centre for Disease Control, Government Health departments, universities etc which verifies the claims, it would be good if these can be added to this thread for others to read. As air-conditioning is prevalent in many countries in hospitals, aged care facilities, offices, shopping centres etc, one would have expected that there would have been controls communicated by the relevant authorities for air-conditioners. The silence seems to suggests that the claims by the air-conditioning servicing expert’s may not stack up.

There is one article about COVID-19 and air-con…

but this was about airflow in the restaurant from air-con and not a result of the air-con or its servicing. The recommended controls in this case are social distancing and fresh air ventilation, and not changing the servicing or operation of the air-con.


I am naturally sceptical when authorities preface statements with “There is no evidence that ……” when my own experience tells me otherwise. When I worked in office blocks (for 40 years) I got frequent colds and flus, when I have months or years away from them, I am a lot healthier. When I fly, especially long-haul flights, I get a cold or flu, but my last flight in December to Paris I wore a surgical mask and did not get sick.

Case study: From the US National Library of Medicine National Institutes of Health
Subject: ‘Airborne spread of measles in a suburban elementary school’

New York Times article: Author - Dr. Allen - director of the Healthy Buildings program at Harvard T.H. Chan School of Public Health.
Title: ‘Your Building Can Make You Sick or Keep You Well’

Scientific Report:
Search on: ‘Assessing the Dynamics and Control of Droplet- and Aerosol-Transmitted Influenza Using an Indoor Positioning System’ at nature dot com (new users (i.e. me) can only put two links in a Choice forum post)

It seems to me that the ‘powers that be’ are simply not really interested in getting to the truth (which they could easily do with proper clinical trials), because it is not commercially expedient.

… or worse still … maybe the authorities are fully aware that air conditioned buildings transmit disease … and that is why they are ordering us to stay home during the coronavirus epidemic.

We all have had similar experiences and wondered what was going on.

Anecdotes and personal experiences do not make for good science. There are too many ways that false associations can be reported and too many ways that bias, conscious or unconscious, can come into play.

I too had the experience that I got colds and flu often when in business. It was most likely because I spent the day meeting people who wouldn’t stay home when they were sick. We know that personal contact transfers viruses. Sharing their droplets through the aircon may have had something to do with it but maybe not too.

Given the supply of droplets would be replaced daily I don’t see the evidence that supports aircon venting would be a significant advantage. One study from 1978 is not strong evidence. If it had been taken up and many studies had replicated these findings and many experts were recommending it things would be different.


The truth seems to be that being in a closed building (irrespective of whether it is airconditioned or not) with poor ventilation increases the risk of one coming into contact with pathogens from another individual. The problem seems to be the building and not necessarily airconditioning. This is possibly why diseases like influenza spike in winter months when indoor living increases due to the cold.

As being in buildings can not be totally avoided, this is possibly why the government has implemented controls for high risk buildings (clubs, pubs, restaurants etc) and also implemented social distancing.

Also, comparing a disease like measles with COVID-19 is disingenuous as they are very different pathogens which react differently in the environment. Even last night if one saw the 7.30 report, the UK medical specialist indicated that COVID-19 can’t even be compared to influenza (which one may think is more similar than measles) as they are very different beasts with very different human reactions to the infection.


I have also found the same article by the same business on and here
and on, and other references using Google search on “Can air conditioning systems in buildings spread coronavirus?”

So it may well be a campaign to promote business for air con industry. I could not find any authoritative reference verifying the claims.


My searching some professional resources also drew a blank. The importance of managing air quality in distributed air conditioning systems is well and long established. Back in history (50years or so) there were numerous enquires into serious concerns with airborne diseases such as legionnaires, often spread by faulty design or poor maintenance.

Keeping it simple, HVAC systems for many decades have been professionally designed. They are required to be properly constructed and maintained to deliver low risk. There are National Building Codes, standards and manuals to provide reliable outcomes.

There are numerous professional service providers who regularly test the air in buildings. These include microbial tests. There are Australian and ISO Standards for the procedures and all test criteria.
EG just one of many,

Regular testing of building air quality provides assurance.

This should go a long way to explain why

The interest of the “powers to be” was responded to decades passed and is now history. The work has been done and the lessons learnt. Legionnaires disease some may remember as an example. It is airborne, highly infectious and has a very high risk for the elderly. Modern HVAC manages this risk. Is COVID-19 any different?

Coronavirus COVID-19 is primarily spread by physical contact and coarse droplet spread, air borne fine vapour spread is a lower risk.

For high risk environments higher standards apply. EG Hospital operating theatres and infectious disease wards.