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Healthy Buildings

Maximum CO2 Concentration Calculator

This tool was developed to support the use of real-time carbon dioxide (CO2) sensors indoors as a way to help evaluate ventilation rates in indoor environments. Users input their target air changes per hour through ventilation and information about the room, and the calculator returns the estimated CO2 concentration.

Important: sufficient clean air delivery can be achieved through any combination of outdoor air ventilation and filtration, but this tool is only for assessing outdoor air ventilation. It is possible to exceed these target CO2 concentrations and still be meeting targets for clean air through filtration.

This guidance does not supersede state or local guidance or guidance from CDC, WHO, or other bodies. It is provided to support efforts to understand ventilation rates in indoor spaces.

1. Room Size

Imperial
Metric
sq. ft. sq. m.
ft. m.

2. Target Air Changes Per Hour

Air changes per hour
=
Clean air rate (ft3/hour)
Clean air rate (m3/hour)
Room volume (ft³)
Room volume (m³)
=
Cubic feet per hour
Cubic meters per hour
Room length × width × height (ft)
Room length × width × height (m)
Note: This tool considers outdoor air ventilation only. If additional impacts from filtration and air cleaners are needed, a combination of ventilation and filtration can be used.
Ideal (6 ACH) Excellent (5-6 ACH) Good (4-5 ACH) Minimum (3-4 ACH) Low (< 3 ACH)
Ideal (6 ACH) Excellent (5-6 ACH) Good (4-5 ACH)
Minimum (3-4 ACH) Low (< 3 ACH)

3. Occupancy

Group 1


Select activity from list »

4. Outdoor CO2 Levels

ppm
Note: If outdoor CO2 measurements were NOT taken, use a default value of 400 parts-per-million.

Result

Configure the settings and then click the button below to calculate.

Strategies to Reduce Infection Risk

If room CO2 consistently exceeds the above calculation:

  1. Consider increasing outdoor air ventilation either by increasing mechanical system operation and/or introducing natural ventilation (e.g., opening windows)
  2. Consider upgrading media filters to higher efficiency versions (e.g., MERV 13), if the HVAC system can accommodate this*
  3. Consider implementing (additional) portable air cleaners.*

This air cleaner calculator can be used to explore portable air cleaner options. Since portable air cleaners increase total effective ACH, but do NOT reduce indoor CO2 concentrations, use the linked portable air cleaner calculator, and NOT indoor CO2 measurements, to assess total effective ACH when using portable air cleaners.

*Strategies two and three increase total effective ACH, but do not change the indoor CO2 concentration. Only strategy one (increasing outdoor air ventilation) reduces the indoor CO2 concentration while also increasing total ACH. Implementing strategy two and/or three will reduce the portion of the total target ACH that will be provided by outdoor air ventilation, which can be helpful if the ventilation system has operational limitations.

About the Calculation

Estimated CO2 concentration is based on a steady state. If the CO2 concentration of an indoor environment is increasing more than 50 ppm per 10 minutes, wait until levels reach a steady state before comparing to the results of this calculator.

This estimate of the steady-state CO2 concentration is based on the number of people, an estimate of their ages and activity level, the room dimensions, and the outdoor air ventilation only. This calculator makes the following necessary assumptions to perform this simplified calculation:

  • Benefits from filtration and portable air cleaners are not captured in this calculation.
  • Indoor air is perfectly mixed (i.e., indoor CO2 concentration is uniform).
  • Indoor CO2 concentrations remain constant over time (i.e., at steady-state).

References and Assumed Calculation Inputs

CO2 Generation Rates (cfm) for Different Metabolic Rates by Age

Age (y) Mean body mass (kg) BMR (MJ/day) CO2 generation rate (L/s)
Level of physical activity (met)
1.0 1.2 1.4 1.6 2.0 3.0 4.0
Males
<1 8.0 1.86 0.0009 0.0011 0.0013 0.0014 0.0018 0.0027 0.0036
1 to <3 12.8 3.05 0.0015 0.0018 0.0021 0.0024 0.0030 0.0044 0.0059
3 to <6 18.8 3.90 0.0019 0.0023 0.0026 0.0030 0.0038 0.0057 0.0075
6 to < 11 31.9 5.14 0.0025 0.0030 0.0035 0.0040 0.0050 0.0075 0.0100
11 to <16 57.6 7.02 0.0034 0.0041 0.0048 0.0054 0.0068 0.0102 0.0136
16 to <21 77.3 7.77 0.0037 0.0045 0.0053 0.0060 0.0075 0.0113 0.0150
21 to < 30 84.9 8.24 0.0039 0.0048 0.0056 0.0064 0.0080 0.0120 0.0160
30 to <40 87.0 7.83 0.0037 0.0046 0.0053 0.0061 0.0076 0.0114 0.0152
40 to <50 90.5 8.00 0.0038 0.0046 0.0054 0.0062 0.0077 0.0116 0.0155
50 to <60 89.5 7.95 0.0038 0.0046 0.0054 0.0062 0.0077 0.0116 0.0154
60 to <70 89.5 6.84 0.0033 0.0040 0.0046 0.0053 0.0066 0.0099 0.0133
70 to <80 83.9 6.57 0.0031 0.0038 0.0045 0.0051 0.0064 0.0095 0.0127
≥80 76.1 6.19 0.0030 0.0036 0.0042 0.0048 0.0060 0.0090 0.0120
Females
<1 7.7 1.75 0.0008 0.0010 0.0012 0.0014 0.0017 0.0025 0.0034
1 to <3 12.3 2.88 0.0014 0.0017 0.0020 0.0022 0.0028 0.0042 0.0056
3 to <6 18.3 3.59 0.0017 0.0021 0.0024 0.0028 0.0035 0.0052 0.0070
6 to < 11 31.7 4.73 0.0023 0.0027 0.0032 0.0037 0.0046 0.0069 0.0092
11 to < 16 55.9 6.03 0.0029 0.0035 0.0041 0.0047 0.0058 0.0088 0.0117
16 to <21 65.9 6.12 0.0029 0.0036 0.0042 0.0047 0.0059 0.0089 0.0119
21 to < 30 71.9 6.49 0.0031 0.0038 0.0044 0.0050 0.0063 0.0094 0.0126
30 to < 40 74.8 6.08 0.0029 0.0035 0.0041 0.0047 0.0059 0.0088 0.0118
40 to <50 77.1 6.16 0.0029 0.0036 0.0042 0.0048 0.0060 0.0090 0.0119
50 to <60 77.5 6.17 0.0030 0.0036 0.0042 0.0048 0.0060 0.0090 0.0120
60 to <70 76.8 5.67 0.0027 0.0033 0.0038 0.0044 0.0055 0.0082 0.0110
70 to <80 70.8 5.45 0.0026 0.0032 0.0037 0.0042 0.0053 0.0079 0.0106
≥80 64.1 5.19 0.0025 0.0030 0.0035 0.0040 0.0050 0.0075 0.0101

Activity Levels (met) for Relevant Occupant Activities

Activity M (met) Range
Calisthenics—light effort 2.8
Calisthenics—moderate effort 3.8
Calisthenics—vigorous effort 8.0
Child care 2.0 to 3.0
Cleaning, sweeping—moderate effort 3.8
Custodial work—light 2.3
Dancing—aerobic, general 7.3
Dancing—general 7.8
Health club exercise classes—general 5.0
Kitchen activity—moderate effort 3.3
Lying or sitting quietly 1.0 to 1.3
Sitting reading, writing, typing 1.3
Sitting at sporting event as spectator 1.5
Sitting tasks, light effort (e.g, office work) 1.5
Sitting quietly in religious service 1.3
Sleeping 0.95
Standing quietly 1.3
Standing tasks, light effort (e.g, store clerk, filing) 3.0
Walking, less than 2 mph, level surface, very slow 2.0
Walking, 2.8 mph to 3.2 mph, level surface, moderate pace 3.5

Occupant Density

The default occupant density was assumed based on ASHRAE Standard 62.1-2019: Ventilation for Acceptable Indoor Air Quality

References

Persily, A. and de Jonge, L., 2017. Carbon dioxide generation rates for building occupants. Indoor air, 27(5), pp.868-879 (Tables 3 and 4.)

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