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How to make indoor air in buildings safe after lockdown

May 21, 2020

We’ve all been through a lot over the past few months, none more so than those who have contracted Covid19, and sadly, the families of those who have succumbed to this terrible disease – our hearts go out to all of those affected.

The lockdown is beginning to ease and workplaces are opening up again, albeit with care and safety in mind.  During the lockdown, many building managers will have switched off air conditioning and turned down ventilation systems, so starting them up again needs to be managed.

Ideally, systems should be regularly maintained, however if they’re not, then it’s important to ask an air conditioning service engineer to carry out an inspection (particularly as we enter the summer period).

What can occupants do to improve air quality in buildings after lockdown?

Open windows

Buildings that have been closed for weeks on end will have stale air inside, so the very first thing to do is to open up windows where it is safe to do so.  At the very least, this will help to freshen up the internal air.

Deep Cleaning

If the building has been closed for 14 days or more, there will be no live Covid19 virus in circulation. That said, it’s essential that deep cleaning is carried out throughout the building to reassure people returning to work.

Air Conditioning Systems

With regards to heating and cooling systems, there is no evidence that they can spread the virus and it will not be present in the system. While it’s important to have the system serviced, it’s advised to keep the temperature at the setpoints already in place prior to the lockdown.  Increasing heat or cooling will have no affect on the control of bacteria – all it will do is cost you more money.

Ventilation Systems

If you have a mechanical ventilation system then your service engineer should have advised you to keep the system running at a lower ventilation rate whilst the building is unoccupied, rather than turn it off.  However, if it has been off for some time, then it’s advised to turn it on for 48 hours prior to occupancy and then set the system to deliver maximum fresh air.

If your system is usually set to run at higher rates during the working day – say 9–5 – then it’s advised to extend the run time by two hours at each end of the day.  If occupants are working around the clock then it should be running 24/7.

Air Handling Units

If you have an air handling unit then it is advised that your service engineer close off recirculation dampers and switch to 100% outdoor air. This is because the system may harbor virus particles in return ducts which could re-enter the building.  This is only advisable whilst the virus is still circulating – only when we know that the virus is no longer a public health concern should recirculation be switched back on.  Your service engineer will outline the effects that this will have on heating and cooling capacity.


Humidifiers tend to be used (if installed) during colder months. While the transmission of some viruses can be limited by changing temperatures and humidity levels, this is not the case with Covid19, as tests have shown that it is quite resistant to environmental changes. 

If you do have a humidifier as part of your air conditioning system, it is advisable to switch it off – you do not need to have it on anyway during warmer weather, and once the Covid19 virus is no longer in circulation, you can switch the humidifier back on during the winter months.

We hope that you find this information useful and if you would like an air conditioning system inspection or service, or if you have any questions at all, please don’t hesitate to contact us.