Ventilation Calculation Tool

An Excel-based tool to assist you in determining the adequacy of the ventilation in your workspace*

*Tool can be used to evaluate classrooms, single offices and small meeting rooms. The levels in this tool are based on classroom occupancies.

Watch John Oudyk's presentation of OHCOW's Classroom Ventilation Tool at a live webinar on December 10, 2021


A snapshot of the Classroom Ventilation Calculation Tool

NOTE:  Downloading the spreadsheet using Firefox as your browser may result in an error message about the extension.
You can open it anyway, or download the file using Chrome or Edge as your browser.

How to Use This Tool

Snapshot of Step 1 of the OHCOW Classroom Ventilation Tool

This is the easy part:

  • you can use a tape measure, or count ceiling/floor tiles
  • there’s apps on some cellphones that let you measure the distance
  • no need to be exact, measuring to the nearest foot will do (area and room volume are automatically calculated)
  • enter the typical and maximum room occupancy (distancing automatically calculated)

Snapshot of Step 2 of the OHCOW Classroom Ventilation Tool

This gets a bit tougher:

  • you probably have to ask someone for this information (maintenance/facilities person, JH&S rep,?) – it is usually found on the building drawings (ventilation plans) – this will be the design flow rate (in cubic feet per minute or cfm)
  • if you have a “ventilation balancing report” (if it’s old, as long as the system hasn’t changed much it should still be relevant) this should give you the measured flow rate
  • the proportion of outdoor air (OA) supply can be fixed at a certain %, but sometimes its variable (then take the maximum and minimum %’s) – again you’ll have to ask for it

Snapshot of Step 3 of the OHCOW Classroom Ventilation Tool

This should be fairly straight forward:

  • you probably have to ask someone for this information (maintenance/facilities person, JH&S rep,?)  but they might not give you the MERV value (there are other ways of classifying filters)
  • if you feel adventurous, ask to have a look inside the unit and see how snuggly the filters fit into place (they won’t work as well if the air leaks around the filters)
  • if you have a look inside the HVAC system, take some pictures – remember, all the air you breath has to go through this unit (it’s the lungs of your building)

Snapshot of Step 4 of the OHCOW Classroom Ventilation Tool

This gets a bit complicated but it’s really “consumer beware!”:

  • you need to find the CADR numbers which aren’t always given – if it’s a HEPA system, the CADR number is the safe as the air flow rate (in cfm – be careful, some manufacturers give the flowrates without the filter)
  • different speeds mean different air flow rates and different noise levels
  • noise level is important to consider since at top speed, most are too loud for classrooms
  • Don’t go for the extras (e.g., ions, UV, vitamin C!)

This is probably most important for naturally ventilated classrooms:

  • a box fan is usually about 1000-2000 cfm (some manufacturers provide this information, some don’t) – noise levels are usually lower than for portable air filters
  • it’s important to specify if you drawing in outdoor air (the best way is to blow the air out one window and let is suck in from another) or just recirculating the air in the room (which doesn’t help and may blow one person’s emissions to another)
  • thermal discomfort becomes an issue but you can dress for that and perhaps provide supplementary heating – we all have to endure some discomfort during a pandemic

(with some guidance on how to interpret the numbers)

  • The CO2 input box is available for you if you have a meter (remember to enter the peak value not the average) – the colour will change based on your measurement value

Post this on your classroom door so those entering know what they’re getting into.

Watch the presentation version of the above steps, complete with audio!

Need help using this tool?

Contact OHCOW and a representative will get back to you asap.

View a complete listing of all OHCOW Occupational Health Apps, Tools and Calculators