There are many articles being submitted with regards to ventilation systems, their efficiency and how to maximize air quality. Most articles deal with spaces ventilated with forced air at reasonable pressure, filtered and distributed through appropriately designed diffusion grills providing the necessary air flows evenly through a defined space.
The large majority of our buildings are not designed this way and rely on natural ventilation with steam and or hot water heating. The air changes in a sanctuary space probably occur once per day at best if doors remain closed during the cooler seasons. Air flow measurement is not necessary in this environment. There is relatively none. This results in a situation where disease transmission is high risk.
USE OF HAND-HELD FOG MACHINES TO TEST VENTILATION?
The use of hand-held fog machines and fake smoke emitters is solely for the purpose of assuring vertical laminar flow in settings like hospital procedure rooms, chemical laboratory applications, electronics and food manufacturing etc. These types of spaces range 6 -10 air changes every hour for safety and hygiene reasons!
To improve air quality in a church setting portable HEPA filter units can be purchased to recirculate air in a sanctuary setting. This is a costly venture.
USE OF FANS TO IMPROVE VENTILATION?
The CDC guidance for ventilation in the link below is excellent. Please note that the majority of the recommendations are for buildings with pressurized HVAC systems with filtration which offer the best protection by changing the air volume in the building 2-3 times per hour based on the design of the system.
Open doors and windows combined with the minor recirculation offered by ceiling fans is the only option available in many churches. This provides relatively low volumetric air changes in the building.
Learn more: https://www.cdc.gov/coronavirus/2019-ncov/community/ventilation.html#fans
RECOMMENDATION
Vaccination, use of PPE, social distancing and limiting the time of occupancy are the best practices that remain in effect.