Introduction
Every fall, offices, schools and retail spaces see more sick days. One of the most overlooked defenses sits above your ceiling: your HVAC system. A well-maintained system dilutes and filters the airborne particles that can carry viruses. A neglected one lets them build up.
Standards and guidelines we recommend:
🔹 Filtration: MERV-13, or the highest rating your system can handle (ASHRAE/CDC)
🔹 Clean air: 5 or more air changes per hour in occupied spaces (CDC)
🔹 Ventilation: Meet the ASHRAE 62.1 outdoor air rates
🔹 Infection control: ASHRAE 241 clean airflow targets and a Building Readiness Plan
🔹 Humidity: Keep indoor relative humidity (RH) at 40–60%
Preventive maintenance essentials:
✅ Change filters on schedule and check that no air bypasses them
✅ Clean coils, drain pans and condensate lines
✅ Check belts, motors and airflow
Seasonal controls and calibration:
- Fall/winter changeover
- Recalibrate outdoor air temperature and humidity sensors so economizers switch over at the right point
- Check minimum outdoor air damper positions with actual airflow readings, not just the control screen
- Test freeze protection and preheat coils
- Check humidifiers and winter humidity setpoints
- Set heat pump balance points and backup heat lockouts so you don’t waste energy
- Update schedules for daylight saving time and holidays
- Add 2 hours of ventilation before and after occupancy
️ Spring/summer changeover
- Reset cooling setpoints and economizer limits
- Make sure dehumidification keeps RH below 60%
- Clean condensate drains before peak cooling season
🔄 Year-round
- Calibrate the CO2 sensors used for demand-controlled ventilation. A drifting sensor can cut outdoor air without anyone noticing.
- Review alarms and trend data for stuck dampers or sensors that don’t agree
Sensors drift. A system that was programmed perfectly in spring can be under ventilating by winter.
Healthier air means fewer sick days, happier customers and equipment that lasts longer. For Washington building owners, a documented O&M program also supports compliance with the Clean Buildings Performance Standard.