ASHRAE 62.1, 55 and 241: Ventilation, Comfort and Clean Air
ASHRAE 62.1 sets the minimum outdoor air for commercial buildings: for each zone, a rate per person plus a rate per square foot. The newest edition is 62.1-2025. California’s Title 24 uses its own version: the larger of 15 cfm per person or a per-square-foot rate, so a 900 sq ft classroom of 30 pupils needs about 450 cfm of outdoor air. ASHRAE 55 sets when people feel thermally comfortable, and ASHRAE 241 sets how much clean air a space needs to cut the spread of infection during a risk period.
These three ASHRAE standards decide how much air a building brings in and how it should feel. 62.1 gives the minimum outdoor air for offices, schools, shops and other non-residential spaces. 55 gives the temperatures, humidity and air speeds most people find comfortable. 241 is newer: it sets how much clean air (outdoor air, filtered air and disinfected air together) a room needs when the risk of airborne infection is high.
The calculator below works out outdoor air for any mix of spaces, the CO₂ level it leads to, what that air costs to heat and cool, and how many clean air changes an hour you get. A second box checks thermal comfort the ASHRAE 55 way. ASHRAE’s text and rate tables are copyright, so this page explains the method and lets you enter the rates from your own copy of 62.1; the rates built in are California’s, from its Title 24 Energy Code, which is public.
1. What 62.1, 55 and 241 cover
| Standard | What it sets, and where | Newest |
|---|---|---|
| 62.1, Ventilation and Acceptable Indoor Air Quality | Minimum ventilation rates and other measures for indoor air quality, in occupied spaces other than dwelling units (homes fall under 62.2) | 62.1-2025 |
| 55, Thermal Environmental Conditions for Human Occupancy | The mix of temperature, radiant heat, humidity, air speed, activity and clothing most people find comfortable, in heated, cooled or naturally ventilated spaces | 55-2023 |
| 241, Control of Infectious Aerosols | Equivalent clean airflow during a period of high infection risk, in new and existing buildings and major renovations | 241-2023, revision under review |
Scope of 62.1 from ASHRAE’s 62.1 fact sheet; editions from ASHRAE’s bookstore and read-only list; 241 from ASHRAE’s June 2023 announcement and its October 2026 Standards Actions.
None of the three is law on its own. 62.1 reaches law through state and city mechanical and energy codes, which copy or adapt its rates: California, for one, puts its own version in Title 24 (section 4). Standards 55 and 241 apply where a code, a contract or a building owner calls them up.
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2. How 62.1 works out outdoor air
62.1’s ventilation rate procedure starts at each zone, a space or group of spaces with the same use and ventilation. It needs outdoor air for the people in it and for the building itself (furnishings, finishes and other sources that do not depend on how many people are there):
| Step | Formula | Where the numbers come from |
|---|---|---|
| Breathing-zone outdoor air | Vbz = Rp × Pz + Ra × Az | Rp (cfm per person) and Ra (cfm per sq ft) by space type, from the standard’s rate table; Pz people, Az floor area |
| Zone outdoor air | Voz = Vbz ÷ Ez | Ez, zone air distribution effectiveness, from the standard’s table by how air is supplied and returned |
| One zone, or 100% outdoor air | Vot = ΣVoz | Add the zones up |
| One unit, several zones | Vou = D × Σ(Rp × Pz) + Σ(Ra × Az); Vot = Vou ÷ Ev | D = system population ÷ sum of zone populations; simplified procedure Ev = 0.88 × D + 0.22 when D < 0.60, else 0.75 |
Multiple-zone equations as printed in the 2025 California Mechanical Code, Section 403.5, which follows 62.1’s simplified procedure.
The per-person part covers what people give off; the per-area part covers the building. That split is why a crowded classroom and an empty warehouse of the same size need very different airflows. Where several zones share one air handler, not everyone is in every zone at once, so occupant diversity (D) trims the people part, while system ventilation efficiency (Ev) adds back what is lost in mixing air between zones.
3. Outdoor-air calculator
Add a zone for each space. In Title 24 mode the rates come from California’s table and the people count defaults to the table’s density; in ASHRAE 62.1 mode you type Rp, Ra and Ez from your copy of the standard. Open the three panels to change who is in the room, the state and heating system, and any filters or air cleaners.
How much outdoor air does my space need?
Indoor CO₂: who is in the room
Energy: what this air costs to heat and cool
Clean air: filters and air cleaners (ASHRAE 241, CDC)
Outdoor air under California Title 24
15.0 cfm (7.1 L/s) per person; 3.3 outdoor air changes an hour
- Classrooms (age 9 -18): 30 people, 900 sq ft: 450 cfm (15 cfm × 30 people is more than 0.15 × floor area); CO₂ about 986 ppm
Demand-controlled ventilation: Title 24 requires CO₂ sensors in Classrooms (age 9 -18) (25 or more people per 1,000 sq ft) if the system has an air economizer, modulating outdoor-air control or more than 3,000 cfm of design outdoor air (Section 120.1(d)3).
Indoor CO₂ once it levels off: about 986 ppm in the most crowded zone (outdoor 429 ppm; children aged 10 to 11 each breathe out 3.94 mL/s of CO₂). Title 24’s sensor limit is 1,029 ppm.
Heating and cooling this air: about $207 a year (87 therms of gas and 252 kWh), 0.5 t CO₂e. Sensible heat only, so a humid climate costs more to cool.
Clean air: 3.3 air changes an hour of outdoor air. CDC suggests aiming for 5 or more air changes an hour of clean air.
Minimum design outdoor air, not a design. Title 24 rates: California’s 2025 Energy Code, Table 120.1-A. CO₂: NIST’s method (Persily 2017) with CDC body-mass data; outdoor CO₂ default: Mauna Loa, week from 1 Nov 2026. Energy: NOAA degree days, EIA commercial prices, EPA eGRID. How it works.
4. California’s version: Title 24
California’s 2025 Building Energy Efficiency Standards (Title 24, Part 6), in force from 1 January 2026, set nonresidential ventilation in Section 120.1. They take 62.1’s idea but change the arithmetic: each zone gets the larger of 15 cfm per person or the area rate, not the sum.
- People. Without fixed seating, the expected number is the designer’s figure or the table’s default density times floor area, whichever is greater. With fixed seats, it follows the California Building Code.
- Demand-controlled ventilation. Spaces with 25 or more people per 1,000 sq ft need CO₂ sensors if the system has an air economizer, modulating outdoor-air control or more than 3,000 cfm of design outdoor air. Rooms under 150 sq ft or under 10 people are exempt, and some spaces (science labs, salons, daycare sickrooms and others with fumes) must not use it.
- The CO₂ limit. Controls keep CO₂ at or below 600 ppm above outdoor air. Outdoor CO₂ can be measured near the intake or assumed to be 400 ppm.
- Before people arrive. For the hour before normal occupancy, the building gets the lesser of its minimum outdoor air or three complete air changes.
The full table follows: 75 space types, each with a default occupant density and an area rate. Title 24 sets each default density at half the maximum occupant load the California Building Code assumes for exits. Rates marked F may drop to zero while the space is in occupied-standby mode.
California Title 24 Part 6 (2025), Table 120.1-A. Every space also takes Rp = 15 cfm per person; the zone gets the larger of 15 × people or Ra × floor area.
| Space | People per 1,000 sq ft | Ra, cfm per sq ft | Air class | Notes |
|---|---|---|---|---|
| Educational Facilities | ||||
| Daycare (through age 4) | 14 | 0.15 | 2 | – |
| Daycare sickroom | 5 | 0.15 | 3 | – |
| Classrooms (ages 5-8) | 25 | 0.15 | 1 | – |
| Classrooms (age 9 -18) | 25 | 0.15 | 1 | – |
| Lecture/postsecondary classroom | 25 | 0.15 | 1 | F |
| Lecture hall (fixed seats) | 71 | 0.15 | 1 | F |
| Art classroom | 25 | 0.15 | 2 | – |
| Science laboratories | 25 | 0.15 | 2 | – |
| University/college laboratories | 25 | 0.15 | 2 | – |
| Wood/metal shop | 10 | 0.15 | 2 | – |
| Computer lab | 25 | 0.15 | 1 | – |
| Media center | 25 | 0.15 | 1 | A |
| Music/theater/dance | 33 | 0.15 | 1 | F |
| Multiuse assembly | 33 | 0.15 | 1 | F |
| Food and Beverage Service | ||||
| Restaurant dining rooms | 33 | 0.15 | 2 | – |
| Cafeteria/fast-food dining | 33 | 0.15 | 2 | – |
| Bars, cocktail lounges | 33 | 0.20 | 2 | – |
| Kitchen (cooking) | 3 | 0.15 | 2 | – |
| General | ||||
| Break rooms | 33 | 0.15 | 1 | F |
| Coffee Stations | 33 | 0.15 | 1 | F |
| Conference/meeting | 33 | 0.15 | 1 | F |
| Corridors | 5 | 0.15 | 1 | F |
| Occupiable storage rooms for liquids or gels | 2 | 0.15 | 2 | B |
| Hotels, Motels, Resorts, Dormitories | ||||
| Bedroom/living room | 3 | 0.15 | 1 | F |
| Barracks sleeping areas | 5 | 0.15 | 1 | F |
| Laundry rooms, central | 5 | 0.15 | 2 | – |
| Laundry rooms within dwelling units | 5 | 0.15 | 1 | – |
| Lobbies/pre-function | 33 | 0.15 | 1 | F |
| Multipurpose assembly | 33 | 0.15 | 1 | F |
| Office Buildings | ||||
| Breakrooms | 33 | 0.15 | 1 | – |
| Main entry lobbies | 33 | 0.15 | 1 | F |
| Occupiable storage rooms for dry materials | 2 | 0.15 | 1 | – |
| Office space | 5 | 0.15 | 1 | F |
| Reception areas | 5 | 0.15 | 1 | F |
| Telephone/data entry | 33 | 0.15 | 1 | F |
| Miscellaneous Spaces | ||||
| Bank vaults/safe deposit | 5 | 0.15 | 2 | F |
| Banks or bank lobbies | 5 | 0.15 | 1 | F |
| Computer (not printing) | 5 | 0.15 | 1 | F |
| Freezer and refrigerated spaces (<50°F) | 0 | 0.00 | 2 | E |
| General manufacturing (excludes heavy industrial and process using chemicals) | 5 | 0.15 | 3 | – |
| Pharmacy (prep. Area) | 5 | 0.15 | 2 | – |
| Photo studios | 5 | 0.15 | 1 | – |
| Shipping/receiving | 2 | 0.15 | 2 | B |
| Sorting, packing, light assembly | 2 | 0.15 | 2 | – |
| Telephone closets | 5 | 0.15 | 1 | – |
| Transportation waiting | 33 | 0.15 | 1 | F |
| Warehouses | 1 | 0.15 | 2 | B |
| All others | 5 | 0.15 | 2 | – |
| Public Assembly Spaces | ||||
| Auditorium seating area | 71 | 0.15 | 1 | F |
| Places of religious worship | 71 | 0.15 | 1 | F |
| Courtrooms | 13 | 0.15 | 1 | F |
| Legislative chambers | 13 | 0.15 | 1 | F |
| Libraries (reading rooms and stack areas) | 10 | 0.15 | 1 | – |
| Lobbies | 33 | 0.15 | 1 | F |
| Museums (children’s) | 17 | 0.15 | 1 | – |
| Museums/galleries | 17 | 0.15 | 1 | F |
| Residential | ||||
| Common corridors | 5 | 0.15 | 1 | F |
| Retail | ||||
| Sales (except as below) | 17 | 0.20 | 2 | – |
| Mall common areas | 17 | 0.15 | 1 | F |
| Barbershop | 17 | 0.40 | 2 | – |
| Beauty and nail salons | 17 | 0.40 | 2 | – |
| Pet shops (animal areas) | 17 | 0.20 | 2 | – |
| Supermarket | 17 | 0.20 | 1 | F |
| Coin-operated laundries | 17 | 0.30 | 2 | – |
| Sports and Entertainment | ||||
| Gym, sports arena (play area) | 10 | 0.15 | 2 | E |
| Spectator areas | 33 | 0.15 | 1 | F |
| Swimming (pool) | 10 | 0.15 | 2 | C |
| Swimming (deck) | 33 | 0.15 | 2 | C |
| Disco/dance floors | 100 | 0.15 | 2 | F |
| Health club/aerobics room | 10 | 0.15 | 2 | – |
| Health club/weight rooms | 10 | 0.15 | 2 | – |
| Bowling alley (seating) | 7 | 0.15 | 1 | – |
| Gambling casinos | 45 | 0.15 | 1 | – |
| Game arcades | 45 | 0.15 | 1 | – |
| Stages, studios | 33 | 0.15 | 1 | D,F |
Notes, in our words: A: For high-school and college libraries, use Public Assembly Spaces: Libraries. B: Rate may not be enough where stored materials can give off harmful emissions. C: Rate does not allow for humidity control. D: Rate does not include special exhaust for stage effects such as dry ice vapours and smoke. E: Where combustion equipment is used on the playing surface or in the space, add dilution ventilation, source control or both. F: Ventilation may be cut to zero when the space is in occupied-standby mode. Air class 1 is clean enough to recirculate anywhere; class 2 may go to some other spaces; class 3 only back to the same space. Source: CEC-400-2025-010-F.
Exhaust
Some rooms need air taken out rather than brought in. Title 24 Table 120.1-B lists minimum exhaust for toilets, kitchens, laboratories, parking garages, salons and others; makeup air can be outdoor, recirculated or transferred air.
California Title 24 Part 6 (2025), Table 120.1-B: minimum exhaust
| Space | cfm per unit | cfm per sq ft | Air class | Notes |
|---|---|---|---|---|
| Animal imaging(MRI/CT/PET) | – | 0.90 | 3 | – |
| Animal operating rooms | – | 3.00 | 3 | – |
| Animal postoperative recovery room | – | 1.50 | 3 | – |
| Animal preparation rooms | – | 1.50 | 3 | – |
| Animal procedure room | – | 2.25 | 3 | – |
| Animal surgery scrub | – | 1.50 | 3 | – |
| Large-animal holding room | – | 2.25 | 3 | – |
| Animal Necropsy | – | 2.25 | 3 | – |
| Small-animal-cage room (static cages) | – | 2.25 | 3 | – |
| Small-animal-cage room (ventilated cages) | – | 1.50 | 3 | – |
| Arenas | – | 0.50 | 1 | B |
| Art classrooms | – | 0.70 | 2 | – |
| Auto repair rooms | – | 1.50 | 2 | A |
| Barber shops | – | 0.50 | 2 | – |
| Beauty and nail salons | – | 0.60 | 2 | – |
| Cells with toilet | – | 1.00 | 2 | – |
| Copy, printing rooms | – | 0.50 | 2 | – |
| Darkrooms | – | 1.00 | 2 | – |
| Educational science laboratories | – | 1.00 | 2 | – |
| Janitor closets, trash rooms, recycling | – | 1.00 | 3 | – |
| Kitchenettes | – | 0.30 | 2 | – |
| Kitchens – commercial | – | 0.70 | 2 | – |
| Locker rooms for athletic or industrial facilities | – | 0.50 | 2 | – |
| All other locker rooms | – | 0.25 | 2 | – |
| Shower rooms | 20/50 | – | 2 | G,H |
| Paint spray booths | – | – | 4 | F |
| Parking garages | – | 0.75 | 2 | C |
| Pet shops (animal areas) | – | 0.90 | 2 | – |
| Refrigerating machinery rooms | – | – | 3 | F |
| Soiled laundry storage rooms | – | 1.00 | 3 | F |
| Storage rooms, chemical | – | 1.50 | 4 | F |
| Toilets – private | 25/50 | – | 2 | E |
| Toilets – public | 50/70 | – | 2 | D |
| Woodwork shop/classrooms | – | 0.50 | 2 | – |
The table’s own notes (A–H) qualify several rows; read them in the source before you design. Source: CEC-400-2025-010-F, Table 120.1-B.
5. CO₂ as a check on ventilation
People breathe out CO₂ at a steady rate, so the CO₂ in a room shows how much outdoor air each person is getting. Once it levels off, indoor CO₂ = outdoor CO₂ + (CO₂ each person breathes out ÷ outdoor air per person). The calculator uses NIST’s method (Persily, 2017): CO₂ output follows from body mass, age, sex and activity, using Schofield’s basal metabolic rate equations, with CDC body-mass data from the latest national survey (NHANES, August 2021 to August 2023) and activity levels from the 2024 Adult Compendium of Physical Activities.
CO₂ breathed out per person, millilitres a second (at 20 °C)
| Who | Sitting: meeting, class or talking (1.3 met) | Sitting: light office work (1.5 met) | Standing: light work (filing, assembling) (1.8 met) |
|---|---|---|---|
| Adults aged 30 to 59 | 4.86 | 5.61 | 6.73 |
| Adults aged 20 to 29 | 5.07 | 5.85 | 7.02 |
| Children aged 6 to 7 | 2.96 | 3.42 | 4.10 |
| Children aged 8 to 9 | 3.45 | 3.99 | 4.78 |
| Children aged 10 to 11 | 3.94 | 4.55 | 5.46 |
| Children aged 12 to 13 | 4.41 | 5.09 | 6.10 |
| Teenagers aged 14 to 15 | 4.85 | 5.60 | 6.72 |
| Teenagers aged 16 to 17 | 5.03 | 5.80 | 6.96 |
Average of men and women, from the CDC’s mean body mass for the age group (NHANES, August 2021 to August 2023), Schofield’s basal metabolic rate equations and NIST’s formula (Persily 2017), with a respiratory quotient of 0.85. Activity levels from the 2024 Adult Compendium of Physical Activities.
Children breathe out less than adults, so a classroom ventilated at the same rate per person reads lower than an office. That is one reason Title 24 controls ventilation to a CO₂ level above outdoor air, measured in each room, rather than to a fixed rate.
6. ASHRAE 55: will people be comfortable?
Standard 55 gives two ways to judge comfort.
- PMV and PPD, for most mechanically heated and cooled spaces. The Predicted Mean Vote rates how a large group would feel on a scale from −3 (cold) to +3 (hot) from six inputs: air temperature, mean radiant temperature, humidity, air speed, activity (met) and clothing (clo). The Predicted Percentage Dissatisfied follows from it. The comfort zone is PMV between −0.5 and +0.5, which is about 10% or fewer dissatisfied. Above 0.1 m/s (20 fpm), the 2023 edition credits air movement with a cooling effect worked out from the Standard Effective Temperature (SET) model, and PMV is taken at the correspondingly cooler temperature in still air.
- The adaptive model, for naturally conditioned spaces where occupants open windows and no mechanical cooling or heating is running. People there accept a wider range that moves with the weather: comfort temperature = 0.31 × prevailing mean outdoor temperature + 17.8 °C, with a band of ±3.5 °C for 80% acceptability and ±2.5 °C for 90%. It applies at 1.0 to 1.5 met, where people can change clothing between 0.5 and 1.0 clo, and outdoor means from 10 to 33.5 °C (50 to 92.3 °F).
Will people be comfortable? (ASHRAE 55)
Thermal comfort under ASHRAE 55 (PMV method)
About 9% of people would be dissatisfied. Within ASHRAE 55’s range for PMV (−0.5 to +0.5).
Adaptive model, for a naturally ventilated space with windows people open: comfortable between 68.9 °F and 81.5 °F for 80% of people (70.7 °F to 79.7 °F for 90%). The operative temperature here is 75.0 °F: inside both bands.
PMV and PPD by the ASHRAE 55-2023 method, with the cooling effect of air above 0.1 m/s (20 fpm) taken from SET, and the adaptive model for naturally ventilated spaces; a port of the open-source pythermalcomfort library (UC Berkeley CBE), checked against it. How it works.
7. ASHRAE 241 and clean air
ASHRAE approved Standard 241, Control of Infectious Aerosols, on 24 June 2023. It works in equivalent clean airflow: outdoor air, plus air cleaned by filters or air cleaners, plus air disinfected (for example by germicidal ultraviolet), all counted as if they were clean outdoor air. It sets how much a space needs while in infection risk management mode, for periods of high infection risk. It does not set general indoor air quality requirements; those stay with 62.1.
241-2023 went through an expedited process during the pandemic, so it was not ANSI-certified. ASHRAE is now revising it under its normal ANSI procedures; the second public review of the revision runs from 9 October to 23 November 2026, with the same title, purpose and scope.
For a simpler yardstick, the CDC suggests aiming for 5 or more air changes an hour of clean air in a room. The calculator’s clean-air panel adds filtered recirculated air (at the filter’s capture rate) and the clean air delivery rate (CADR) of portable air cleaners to the outdoor air, and compares the total with that target.
8. Getting the standards
ASHRAE lets anyone read some standards free, read-only, on its website. The list includes 62.1-2022, 55-2023 and 62.2-2025; the read-only copy cannot be downloaded. The current 62.1-2025 is sold by ASHRAE and the ANSI webstore, and ASHRAE keeps it under continuous maintenance through addenda: Addendum a to 62.1-2025 was approved on 30 June 2026. Your local code may call up an older edition, so check which one your jurisdiction adopted before designing to it.
9. How these figures are made
- Outdoor air. Title 24 mode: for each zone, people = the larger of what you enter or density × area ÷ 1,000; outdoor air = the larger of 15 × people or Ra × area; the system total is the sum. 62.1 mode: the formulas in section 2, with Ez = 1.0 if left blank. 1 cfm = 0.4719 L/s. Air changes an hour = 60 × cfm ÷ (floor area × ceiling height).
- CO₂. CO₂ per person (L/s) = 0.85 × BMR × met × (T ÷ P) × 0.000211, at 20 °C and 101.325 kPa (Persily, Equation 4), averaged across men and women. BMR from Schofield’s equations at the CDC’s mean body mass for the age group (adults 30 to 59: the mean of the 30s, 40s and 50s rows). Each zone is treated as well mixed and receiving its own outdoor air.
- Energy. Sensible heat only: Btu a year = 1.08 × cfm × degree days × 24 × (hours occupied ÷ 168) × (1 − heat recovery). 1.08 = 0.075 lb/ft³ × 60 min × 0.24 Btu/lb·°F. Heating and cooling degree days (base 65 °F) are NOAA’s 1991–2020 state normals; Alaska, Hawaii and DC have none in that set, so enter your own. Prices are EIA’s average commercial electricity and gas prices for the state; CO₂e from EPA eGRID state factors and EPA’s natural gas factor. Moisture (latent) load is left out, so humid climates cost more to cool than shown. Defaults (40 hours a week, 90% furnace, cooling COP 3) are ours: change them.
- Comfort. PMV, PPD, SET cooling effect and the adaptive model are ported from pythermalcomfort, the open-source library from UC Berkeley’s Center for the Built Environment. Relative air speed and dynamic clothing are applied above 1.0 and 1.2 met as the library does. The port reproduces the library’s published test values, including PMV 4.51 at 41 °C, 2 m/s, 0.7 met and 2.1 clo.
- Title 24 table read by a script. All 75 rows of Table 120.1-A and 34 of Table 120.1-B are parsed from the California Energy Commission’s PDF; the build stops unless the row counts and spot-check rows match.
- CO₂ rates from NIST’s formula, checked both ways. NIST gives the same formula at 0 °C and at any temperature and pressure; we use the general form at 20 °C and confirm it reproduces the 0 °C form. An adult sitting in a meeting comes out at 4.9 mL of CO₂ a second.
- Browser and server agree. The calculator in your browser and the copy the server renders run the same arithmetic; a test compares them for thousands of inputs before each release.
Frequently asked questions
ANSI/ASHRAE Standard 62.1, Ventilation and Acceptable Indoor Air Quality, sets minimum ventilation rates and other measures for indoor air quality in buildings other than homes. Each zone needs a rate per person plus a rate per square foot of outdoor air. The newest edition is 62.1-2025.
For each zone, multiply the people by the per-person rate (Rp), add the floor area times the per-area rate (Ra), and divide by the zone air distribution effectiveness (Ez). Add the zones for a single-zone or 100% outdoor-air system; for one unit serving several zones, apply occupant diversity and system ventilation efficiency. The calculator does all of it.
62.1 covers spaces other than dwelling units; 62.2 covers dwelling units. Since the 2016 editions, all residential occupancies sit in 62.2.
Under California’s Title 24, a 900 sq ft classroom with 30 pupils needs 450 cfm (15 cfm per pupil, which is more than 0.15 cfm per sq ft of floor). Under 62.1 it depends on the rates in your edition; enter them in the calculator to compare.
Neither 62.1 nor 55 sets an indoor CO₂ limit. California’s Title 24 uses CO₂ to control ventilation, keeping it at or below 600 ppm above outdoor air (about 1,000 ppm with outdoor air near 400 to 430 ppm). The level a room reaches depends on who is in it: the CO₂ section shows rates by age and activity.
Between −0.5 and +0.5, which means about 10% or fewer of people would be dissatisfied. The comfort check works it out from temperature, radiant temperature, humidity, air speed, activity and clothing.
A comfort range for naturally ventilated spaces where people open windows and no mechanical cooling or heating runs. The comfort temperature is 0.31 times the prevailing mean outdoor temperature plus 17.8 °C, with ±3.5 °C for 80% acceptability and ±2.5 °C for 90%.
ASHRAE Standard 241, Control of Infectious Aerosols, approved in June 2023, sets the equivalent clean airflow a space needs during a period of high infection risk: outdoor air, filtration and disinfection counted together. A revision is in its second public review until 23 November 2026.
Yes, read-only: ASHRAE’s free viewing list includes 62.1-2022 and 55-2023. You cannot download them there; the current 62.1-2025 is sold by ASHRAE and the ANSI webstore.
Sources and downloads
- California Energy Commission, 2025 Building Energy Efficiency Standards for Residential and Nonresidential Buildings (CEC-400-2025-010-F): Section 120.1, Equation 120.1-F, Tables 120.1-A and 120.1-B.
- California Building Standards Commission, 2025 California Mechanical Code (Title 24, Part 4), Section 403.5, multiple-zone recirculating systems.
- ASHRAE, Read-only versions of ASHRAE standards; Standards 62.1 and 62.2; Addendum a to Standard 62.1-2025 (approved 30 June 2026); Standard 62.1-2016 fact sheet (scope and purpose).
- ASHRAE, ASHRAE approves groundbreaking standard to reduce the risk of disease transmission in indoor spaces (24 June 2023); Standards Actions, 9 October 2026 (second public review of BSR/ASHRAE Standard 241P); AIHA, ASHRAE approves standard on controls for infectious aerosols in indoor spaces (29 June 2023).
- US Centers for Disease Control and Prevention, NIOSH, Aim for 5 air changes per hour of clean air.
- Andrew Persily, A New Approach to Estimating Carbon Dioxide Generation Rates from Building Occupants, ASHRAE Journal 59(7), 2017 (NIST author manuscript).
- National Center for Health Statistics, Anthropometric Reference Data for Children and Adults: United States, August 2021–August 2023, Tables 1 and 3.
- 2024 Adult Compendium of Physical Activities, volunteer activities, codes 21000, 21005 and 21015.
- Center for the Built Environment, UC Berkeley, pythermalcomfort (MIT licence): pmv_ppd_ashrae, cooling_effect, two-node SET model, adaptive_ashrae, and its typical activity and clothing tables.
- NOAA, 1991–2020 climate normals (state heating and cooling degree days, base 65 °F); US Energy Information Administration, average commercial electricity and natural gas prices by state; US EPA, eGRID state emission rates and the GHG Emission Factors Hub; via GreenCalculus MasterBrain.
Download the data, free to reuse under CC BY 4.0 with a link to this page (the Title 24 tables are California’s public regulation):
- t24-ventilation.csv: Title 24 Table 120.1-A, 75 space types, occupant density, Ra, air class, notes
- t24-exhaust.csv: Title 24 Table 120.1-B, 34 exhaust rates
- co2-generation.csv: CO₂ per person by age group and activity, with body mass and basal metabolic rate
What changed in this revision
Version 1.0 (31 October 2026): First publication.