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Heating, ventilation, and air condition (HVAC) systems

Heating, ventilation, and air condition (HVAC) systems can help increase indoor air flow by pulling in outdoor air. They also filter both inside air and outdoor air entering the building. This helps clean the air indoors, reducing the risk of spreading disease.

Consult with your building engineer or certified HVAC specialist to maintain and optimize your HVAC system. If you rent, talk to your landlord. If you don’t have an HVAC system, increase air flow by opening windows and doors when the air outside is clean and it's safe to do so.

You can determine how much air flow you need in your space (and if you should also use other strategies) by considering a few factors, including the number of people in the space and the size of the space. In some situations, measuring CO2 can help indicate when additional ventilation and/or filtration are needed.

Operating an HVAC system

  • Most HVAC systems work by bringing in outdoor air and mixing it with air circulating inside. Work with your HVAC specialist to set your HVAC system to reduce the amount of air recirculated and to bring in as much outdoor air as possible.
    • Experts recommend higher ventilation rates up to 21.2 cubic feet per minute per person, and minimum 5 air changes per hour to reduce the risk of airborne infectious disease transmission. Read more in this Lancet Commission report.
  • Work with your building engineer or HVAC specialist to adjust the airflow to prevent air with pollutants/germs moving from one area to another.
  • It's generally helpful to bring in more outside air during the whole day – during normal operations, between group and work shifts, and while cleaning and disinfecting. Maximizing air flow during these periods helps quickly replace the air in the room with fresh, clean air. (Note: this does not apply during wildfire smoke events.)

HVAC filters

If you are recirculating air, make sure it is filtered. Recirculating unfiltered air can increase the spread of respiratory diseases (like COVID-19):

  • If your system can handle them, use MERV 13 HVAC filters or higher or their ISO ("3M" brand) and Filter Performance Rating (FPR) equivalents ("The Home Depot" brand).
  • MERV 8 filters are the most commonly-used HVAC filters, but they capture 30-40% fewer particles (like pollutants and airborne viruses) than a MERV 13 filter. MERV 10 and 12, while more effective than MERV 8, are still not as effective as MERV 13.
  • Ask your HVAC specialist about upgrading to MERV 13 filters or the highest rated filters your system can handle. The all-in cost (labor, materials, energy) of upgrading from MERV 8 to MERV 13 is about $1.50 per month for a 5,000 square foot office, according to the Lancet Covid-19 Commission Task Force on Safe Work, Safe School, and Safe Travel.
  • If it's not possible to upgrade to MERV 13, consider also using portable HEPA air cleaners or DIY box fans with MERV 13 filters attached

HVAC maintenance

Maintain your HVAC system to ensure maximum air flow, efficiency and filtration:

  • Change filters as needed. Clogged filters make it harder to improve indoor air quality. Visually inspect filters monthly to ensure they are not thickly coated with dust.
  • Inspect and clean the entire HVAC systems regularly. Make repairs quickly to prevent serious issues.
  • Open windows and doors to increase outside air. This may add to heating costs during colder weather, but is an important precaution against airborne viruses like COVID-19.
  • Ask your building engineer to share maintenance and air quality data so you can be aware of health and safety measures in place. If you are the building engineer, proactively share this information.

How to know if you're getting enough ventilation

  • We receive many questions about ventilation and how to know if it’s enough. Ask your HVAC specialist or building manager to set the air flow in the space to achieve a minimum of 5 air changes per hour.
  • In some situations, measuring CO2 can indicate when additional ventilation or filtration are needed. However, results from built-in CO2 monitors can be expensive to install and complicated to interpret. Handheld monitors can be more cost effective and should be used to monitor CO2 levels in occupied spaces.
  • The CDC recommends increasing ventilation when CO2 levels exceed 800 ppm. If increasing ventilation isn’t possible, they suggest increasing filtration.
  • Building managers can use new tools, like this CO2 calculator, that incorporate CO2 levels to determine when ventilation and filtration should be increased.

Questions to ask an HVAC specialist

  • What type of filters does my HVAC system currently use?
    • Ideally your HVAC will use MERV 13 filters or higher (14, 15, etc.) or the ISO or FPR equivalent (3M or Home Depot brand).
  • How often do I need to change my filters?
    • Your HVAC specialist should know how often to replace filters or describe what a dirty filter that needs replacing looks like.
  • How often should I clean or inspect my HVAC system?
    • At a minimum your system should be inspected, serviced, and cleaned once a year. Inspection schedules will depend on type and use of the building. If a system has both heating and cooling functions, heating should be checked in the fall and air conditioning checked in the spring. Additionally, you should visually inspect your filters during wildfire smoke events to ensure they aren't thickly coated with dust.
  • Does airflow in my building move in the direction of clean to less-clean air? 
    • Your HVAC specialist or another expert, such as an industrial hygienist, can assess the air flow in a building using special tools. For example, if a facility has an isolation room for sick patients, the specialist can determine if HVAC system changes can prevent air moving from that space to other areas. 
  • How do I know my HVAC system is working well?
    • HVAC specialists assess how well the system is functioning during their regularly scheduled inspections.

Additional resources

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