Bulletin – Indoor Air Quality for Residential Buildings

Air Filtration and Indoor Air Quality - Unionville Heating and Air Conditioning

Unionville Heating and Air Conditioning is continuously monitoring and gathering information to provide their customers with the best recommendations and implementation for residential HVAC systems.  Our goal for learning about advancements in technology is to apply these learnings to help keep us all safe. We care!

This bulletin is issued by ASHRAE to address the COVID-19 pandemic and it’s effects on HVAC

The American Society of Heating, Refrigerating and Air-Conditioning Engineers, (ASHRAE) is a global professional society of over 55,000 members committed to serve humanity by advancing the arts and sciences of heating, ventilation, air conditioning, refrigeration and their allied fields. ASHRAE has established a Task Force to help deploy technical resources to address the challenges of the COVID-19 pandemic and possible future epidemics as they relate to the effects of heating, ventilation, and air-conditioning (HVAC) systems on disease transmission. Guidance and building readiness information for different operational conditions have been developed for several building types, including commercial; residential; schools and universities; and healthcare facilities.

Home is usually the safest indoor space and we stay there as much as possible to protect ourselves and to help mitigate the spread of COVID-19. ASHRAE recommends following CDC guidance on minimizing contact, wearing cloth face masks and creating a household plan. ASHRAE’s residential building guidance supplements the CDC guidance with general recommendations for minimizing virus transmission through the air using the home’s HVAC equipment and controls. ASHRAE’s website provides additional details and the most up-to-date information on residential buildings, as well as answers to Frequently Asked Questions. Please consult the full guidance for important details and consider reaching out to qualified design professionals for detailed analysis as needed.

  • Maintain thermal comfort: Avoid extremes of temperature by operating and maintaining the building and the heating and cooling equipment to keep temperature and humidity in normal ranges, which are generally 68-78 Fahrenheit (20-25 Celsius) and 40-60% relative humidity.
  • Filtration for Homes with Forced-Air Systems: Upgrade filters to high-efficiency filters (MERV 13 or the best the system can accommodate), if practical. Adjust the fan setting to run even if not currently heating or cooling.
  • Ventilation (with outdoor air): Increase mechanical ventilation, if practical. If the house is not equipped with a mechanical system that provides whole house ventilation opening multiple windows is an acceptable alternative for a single-family home. Whole-house “summer cooling” fans or economizers may also be used to increase outdoor air ventilation. Weather may make this impractical at times.
  • Restrooms: Operate exhaust fans in bathrooms, toilets and lavatories preferably continuously. Toilet lids should normally remain closed, especially prior to flushing. Do not allow plumbing traps to become dry.
  • Air Purifiers: Stand-alone air cleaners (often called air purifiers) with HEPA particle filters can help remove suspended small airborne particles that can contain viruses and the fine particles typical of wildfires. When either is a risk, operate the device(s) continuously. In general, the larger the flow the better. Those with ultraviolet disinfection can further reduce virus risk.
  • Multi-Family Homes: Minimize the use of open windows to limit the potential transfer of infective air from nearby apartments. Seal any large openings in walls or ceilings or gaps around plumbing or electrical penetrations that could allow air to flow into the dwelling unit from other units in the building.
  • Create an Isolation Space for Infected Household Members: Barriers should be used between the isolated and common spaces. The isolation space should have flow into it from other spaces which can be achieved using exhaust fans temporarily installed in windows or bathroom exhaust fans if the isolation space has its own bathroom. Air purifiers should be considered.
  • Create a Protected Space for High-Risk Household Members: Barriers should be used between the protected and common spaces. The protected space should have air flow out of it to other spaces which can be achieved using supply fans temporarily installed in windows. Air purifiers should be considered.

The information above is provided as a service to the public. While every effort is made to provide accurate and reliable information, this is advisory, and is provided for informational purposes only. They are not intended and should not be relied upon as official statements of ASHRAE.

Government of Canada COVID-19: Guidance on indoor ventilation during the pandemic

Replace filter with a high MERV rating

The Public Health Agency of Canada (PHAC) has developed a guide to inform Canadians about how indoor ventilation, combined with other recommended public health measures, can reduce the spread of COVID-19. The guide also provides practical tips on improving indoor air, ventilation and filtration to help reduce the spread of COVID-19.

The complete content of this guide is available on the Government of Canada website.

Please read the key messages

  • Limit indoor gatherings
  • Open windows and doors
  • Consult an HVAC professional
  • Consider avoiding the area

Influence of ventilation on risk of aerosol transmission

If a person who is infected is in an indoor space, build-up of viral particles will depend on:

  • how infectious the person is
  • the activities the person undertakes
  • the size of the space and its ventilation

The smaller the room, the faster the build-up of particles containing SARS-CoV-2 virus. In larger spaces, it may take longer for virus-containing aerosols to build up throughout the room. Good ventilation will:

  • move outdoor air into the space
  • dilute potentially contaminated air
  • remove contaminated air through vents or open windows

In any size of room, close proximity can result in high-risk exposure, regardless of ventilation.


There are many ways to improve ventilation to mitigate the transmission of infectious diseases. The most appropriate measures depend on the characteristics of the particular setting. One way to improve ventilation is by opening exterior doors and windows for a few minutes, ideally with more than one open at a time.

Opening windows in winter may not always be comfortable or possible. Doing so for a few minutes at a time during the day can still improve air quality, with minimal impact on the indoor temperature. If occupants will be indoors for longer periods, for example at schools, occupants should have regular outdoor breaks, to allow for ventilation of the room.

An HVAC system will exchange indoor air a certain number of times per hour as a part of regular operation. To increase ventilation, run your HVAC system fan continuously at a low speed to provide air movement and filtration without unwanted draft. Within non-residential buildings, run the system for 2 hours at maximum outside airflow before and after the building is occupied. Bathroom and kitchen exhaust fans that are vented to the outside can also be used to help remove potentially contaminated air, where appropriate.

Most HVAC systems will recirculate some air through the indoor space, making it important to:

  • ensure that filters are well sealed without a bypass
  • clean or change your filters regularly per manufacturer’s recommendations
  • select filters with higher MERV ratings that are more efficient at removing particles

This should be done within the specifications of your HVAC system and in consultation with an HVAC professional.

Portable or ceiling fans, or single unit air conditioners may circulate air within the room, but they do not exchange air or improve ventilation. If using a window air conditioner unit or a fan is necessary, aim the air stream away from people to reduce the spread of potentially infectious droplets or particles.

Please contact us if you have any concerns or questions about how to improve your indoor air quality.  We are happy to provide a free no-contact consultation.