The following information is a summary of the COVID-19 guidance developed by REHVA – the Federation of European
Heating, Ventilation and Air Conditioning Associations, with additional content from CIBSE – the Chartered Institution of
Building Services Engineers and BESA – the Building Engineering Services Association.
The full published articles can be found here
The advice in this document is for building owners/managers and operators when reopening buildings
following a period of inactivity and considering the requirements for the ventilation system.
It is to be read in conjunction with any information available on, or linked from
The document is written in the context of a temperate oceanic climate as experienced in the UK and
will outline the main actions you should take regarding your ventilation. Section 3 explains
different ventilation systems within buildings and their key operating characteristics, Section 4
then explains how you should operate these different types of ventilation to reduce the risk of
SARS-CoV2 transmission. This includes preparing the ventilation system for the re-occupation of the
building, considerations about operating it during re-occupation.
In some cases the occupancy of a room/zone may be reduced due to social distancing criteria and
ordinarily this would result in a reduction of the ventilation airflow required. However, in order
to reduce risks associated with viral transmission the number of air changes has to be as high as
It is primarily intended for application in non-domestic buildings excluding health care and
hospital buildings where NHS and PHE guidance should be sought.
If a confirmed case or case(s) of Covid-19 has been identified from a building user then please
consult current Government advice.
The advice contained in this document specifically concerns the ventilation provision in indoor
spaces and presents advice as to what can be done to reduce the risk of viral infection
transmission indoors, as such it should be read in conjunction with advice on social distancing,
cleaning and other building management advice.
The key actions are:
– Understand your ventilation system
– Run your ventilation at higher volume flow rate; this may require changes to CO2 set points (for
both mechanical ventilation and automated windows)
– Avoid recirculation/transfer of air from one room to another unless this is the only way of
providing adequately high ventilation to all occupied rooms
– Recirculation of air within a single room where this is complemented by an outdoor air supply is
– If applicable enthalpy (thermal) wheels should be switched off, but the pressure difference will
need to be maintained between supply and extract to minimise any leakage flow from the extract to
Specialist localised exhaust ventilation
In some settings specialised extract ventilation is used to remove lots of air from a specific
location, for example; cooker hoods in kitchens, local exhaust on CNC machinery, fume hoods.
Although these systems generally remove large volumes of air, it is important to ascertain where
the replacement air is coming from which replaces that exhausted from the room. It may come
directly from outside through windows/doors, or air may enter from other rooms/zones e.g. adjacent
corridors or adjoining rooms. In the case of large factory floors replacement air is likely to be
from the outside. Specialised local exhaust ventilation is the subject of specific workplace
regulations and the Institute of Local Exhaust Ventilation Engineers provide more specialist advice
and practitioners who have particular expertise in these systems.
3.4 No obvious ventilation strategy
Some spaces may not have an identifiable ventilation system. For example, it is common for there to
be no ventilation in corridors or staircases as these are deemed to be transient spaces and they
rely on air infiltration from neighbouring spaces. However, rooms/zones that are occupied routinely
without any obvious ventilation strategy are going to be a significant
risk and the ventilation provision should be addressed.
Government latest cases