Winter inversions in Utah cause pollution and other contaminants to build up near the ground, creating unhealthy air for days at a time. Whenever winter inversions occur in Utah, we want to keep as much outdoor air from entering our homes and further filter the air that we recirculate indoors. Running your HVAC system correctly can help you decrease indoor pollution levels while maintaining comfort in your home.
For most Utah homes, your HVAC system should be on recirculation with the windows closed until local officials announce that the outdoor air quality has improved.
HVAC System and Airflow During an Inversion
- Keep windows and doors closed and run your HVAC system in recirculation mode so that indoor air cycles repeatedly through your system filter.
- Use higher efficiency filters such as MERV 13 if compatible with your system. Otherwise, utilize portable HEPA air purifiers.
- Turn off any fresh-air intake or economizer modes which bring outdoor air into your home.
- Don’t burn candles or engage in other activities that create indoor air pollutants.
- Replace HVAC filters after inversion events to remove trapped particles.
Your heating and cooling system mechanically moves air from your home’s ducts through filters and other components. Understanding how air flows through your system will help you minimize polluted outdoor air from entering your home during an inversion event.
Methods for air exchange through your HVAC system include:
- The fan
- Outdoor air intake dampers
- Dedicated ventilation equipment such as heat recovery ventilators (HRV)
Learning how to manipulate these functions will allow you to minimize outdoor air infiltration.
Recirculating Air vs Bringing in Outdoor Air
Air that is being recirculated indoors passes through your HVAC system’s air filter repeatedly. Each time indoor air cycles through the filter, less outdoor air pollution enters your home.
The opposite happens when your HVAC system brings outdoor air into your ductwork. Air pollution such as PM2.5 and ozone can get into your house while local air quality is impacted by inversions.
If you need to bring in outdoor air for humidity control or odor concerns, limit the amount of time outside air is brought into your home. Only introducing outside air for a few hours after local air quality returns to normal will keep additional pollution out of your home.
Misconceptions About Bringing in “Fresh Air”
Fresh air is not always better than indoor air. Inversions cause outdoor air quality to become much worse than indoor air.
Typically, we think that by opening windows or forcing outdoor air into our homes, we are decreasing indoor particulate matters.
Research has shown that using MERV 13 filters and running portable HEPA air cleaners throughout your home reduces indoor air pollution during smog alerts.
Minimize Outdoor Air Intake on Red Air Days
The main goal for air quality while an inversion is in effect should be filtration. Minimize outside air infiltration as much as possible by:
- Running your HVAC system fan in recirculation mode.
- Installing a high-efficiency HVAC filter.
- Turning off dampers which pull outdoor air into your HVAC system.
- Eliminating activities that create indoor smoke or dust.
Running the fan continuously can create issues with increased energy use. Set your fan to run periodically between heating or cooling cycles.
Turn Off Fresh Air Intake Modes
Outside air enters a home through forced and natural means. While forced air infiltration can be controlled through your thermostat and duct system, natural infiltration can take place through:
- Poorly sealed windows and doors
- Weatherstripping missing from windows and doors
- Door sweeps absent from exterior doors
- Attic hatches and wall penetrations
- Pipes, wiring, and other openings found through floors and walls
- Duct joints and connections
Most infiltration takes place through small cracks and openings around the house. Any gaps and cracks create pressure imbalances that suck outdoor air into the home.
Consider hiring a contractor to perform blower-door testing on your home. The results will determine how much and where air infiltrates your home. From there, you can prioritize sealing based on the test results.
Supplemental Indoor Air Purification
Using high-efficiency HVAC filters and portable air cleaners helps improve indoor air quality when pollution levels are elevated during inversion events.
Consider these options to reduce PM2.5 particles inside your home:
- Use MERV 13 or higher filters in your HVAC system.
- Utilize portable HEPA air cleaners.
- Install whole-home air purification systems.
Whole Home Air Purification Systems
These systems are designed to connect to your return ducts and help improve air filtration of circulated air.
Contact your HVAC technician to verify if your system is compatible with high-efficiency air filters. Some HVAC systems have limited airflow that will alarm or even damage the system when higher-rated filters are installed.
Portable Air Cleaners
Use portable HEPA air cleaners in bedrooms and common living areas. Follow manufacturer instructions for optimal performance.
- Select a unit that is appropriate for the room size.
- Run the air cleaner continuously while indoors during an inversion event.
- Position the portable air cleaner in sleeping areas and common seating areas.
- Replace filters as recommended by the manufacturer.
Don’t use air purifiers that generate ozone as a by-product. Ozone is harmful to your lungs and can aggravate allergy and asthma symptoms.
Final Thoughts
During an inversion in Utah, you want to run your HVAC system on recirculation and avoid introducing outdoor air into your home. Using high-efficiency HVAC filters and running portable HEPA air cleaners will help decrease airborne particulates.
Once the outdoor air quality returns to normal, you can resume regular ventilation practices. Follow local air quality reports to determine when it is safe to open windows and bring outdoor air into your home.
Frequently Asked Questions
Can I run my HVAC when the Air Quality Index is red?
Yes! Running your HVAC system will improve filtration when set to recirculation using a high-efficiency HVAC filter.
How should I set my thermostat fan during an inversion?
Set the fan switch to ON instead of AUTO if you want improved filtration. Leaving your fan on continuously will cycle more air through the filter.
What air filter should I use?
MERV 13 or higher air filters are best at trapping fine particulate pollution. Consult your HVAC technician to ensure your system is compatible with these filters.
When can I open my windows?
Do not bring outdoor air into your home until after air quality levels return to yellow or green. Check with your local officials to see when outdoor air quality is safe.
What maintenance can I perform during inversion season?
Replace HVAC filters frequently during inversion season, seal air leaks, and run portable HEPA air cleaners in your bedroom and living areas. Some may choose to stay in hotel rooms with individual air filtration until outdoor pollution levels decrease.
