ASHRAE thermal comfort standards, chiefly ASHRAE Standard 55, define the indoor conditions in which most people in a building feel comfortable. The standard weighs six factors: air temperature, radiant temperature, air speed, humidity, activity level and clothing. For mechanically conditioned spaces, the usual target is a predicted mean vote (PMV) between -0.5 and +0.5, a band that corresponds to roughly 10% of people being dissatisfied. Naturally ventilated spaces can use the separate adaptive method.
Ask ten people in a building whether the temperature feels right, and you’ll usually get ten different answers. That’s precisely the problem ASHRAE thermal comfort standards were built to solve: turning something as subjective as “feeling comfortable” into a measurable, designable target. For architects, facility managers, and anyone specifying HVAC or thermal comfort systems, understanding ASHRAE 55 isn’t optional technical trivia. It’s the foundation every comfort-related design decision gets measured against.
What Are ASHRAE Thermal Comfort Standards?
ASHRAE, the American Society of Heating, Refrigerating and Air-Conditioning Engineers, publishes the standards most widely referenced worldwide for evaluating and designing indoor thermal environments. The primary document is ASHRAE Standard 55: Thermal Environmental Conditions for Human Occupancy, which defines the combinations of environmental and personal factors that produce acceptable thermal comfort for most occupants in a space. You can browse the standard and its updates on the ASHRAE website.
ASHRAE 55 doesn’t prescribe one “correct” temperature. It defines a comfort zone built from several variables interacting at once, which is why two buildings can both comply with the standard and still feel noticeably different to the people inside.
The Six Factors Behind ASHRAE 55
ASHRAE thermal comfort standards are built around six core variables, four environmental and two personal.
Environmental factors
- Air temperature, the most obvious variable, but far from the only one that matters
- Radiant temperature, the temperature of surrounding surfaces, which changes how warm or cool a space feels independent of air temperature
- Air speed, since moving air speeds up heat loss from skin and shifts perceived comfort
- Humidity, which determines how effectively the body can cool itself through evaporation
Personal factors
- Clothing insulation (clo value), since what occupants wear significantly changes their comfort range
- Metabolic rate (met value), since activity level changes how much heat the body generates and needs to shed
The ASHRAE Thermal Sensation Scale and the PMV/PPD Model
Much of ASHRAE 55 thermal comfort assessment rests on a simple idea: ask people how they feel, then predict the average. Researchers use a seven-point ASHRAE thermal sensation scale:
- +3 Hot
- +2 Warm
- +1 Slightly warm
- 0 Neutral
- -1 Slightly cool
- -2 Cool
- -3 Cold
The Predicted Mean Vote (PMV), developed by Danish researcher P.O. Fanger, forecasts the average vote of a large group of people on this scale. The Predicted Percentage of Dissatisfied (PPD) converts that vote into the share of occupants likely to feel uncomfortable, even when the average looks fine. ASHRAE 55 recommends keeping PMV between -0.5 and +0.5 in mechanically conditioned spaces, which holds PPD at roughly 10%.
That gap between the average and the individual matters in practice. A space can post an acceptable average score and still leave a stubborn minority shivering or sweating, which is why the standard sets a PPD threshold instead of assuming comfort for everyone.
ASHRAE Comfort Zone: Temperature Range and Comfort Chart
So what does the ASHRAE comfort zone look like in degrees? Here is the honest answer on the ASHRAE temperature range, plus how to check your own building.
Is there an ASHRAE recommended temperature?
Not a single one, so treat any ASHRAE temperature range quoted online with care. Commonly cited ranges are about 23 to 26 degrees C in summer clothing and about 20 to 24 degrees C in winter clothing at moderate humidity. Treat these as ballpark figures, not targets. The thermal comfort range shifts with humidity, air speed, activity and clothing, which is exactly why the standard defines a zone instead of a number.
How to read an ASHRAE comfort chart
An ASHRAE comfort chart plots operative temperature against humidity and shades the combinations most people find acceptable. You will usually see two overlapping zones, one for light summer clothing and one for heavier winter clothing. If your conditions land inside the shaded area for your occupants’ clothing and activity, you are inside the ASHRAE comfort zone. To test your own numbers, use the free CBE Thermal Comfort Tool, which runs the ASHRAE 55 method for you.
The ASHRAE Adaptive Comfort Model
ASHRAE 55 also includes an adaptive comfort model for naturally ventilated spaces. It recognises that occupants adapt to outdoor conditions and to their own behaviour, such as changing clothing or opening a window, so it allows a wider acceptable range than the tighter band expected in fully conditioned buildings. We unpack the equation, the 80% and 90% acceptability bands and a worked example in our guide to the ASHRAE 55 adaptive comfort model.
Why ASHRAE Thermal Comfort Standards Matter for Building Design
Meeting ASHRAE thermal comfort standards isn’t just about occupant satisfaction, though that alone has real consequences for productivity, wellbeing and complaint volume in commercial buildings. These standards also intersect directly with:
- Green building certifications, since LEED, WELL and other frameworks reference ASHRAE 55 compliance as part of their indoor environmental quality criteria (see our guide to GRIHA rating for commercial buildings)
- Energy performance, since HVAC systems designed around actual comfort variables, rather than blunt temperature setpoints, tend to run more efficiently (see our guide on reducing HVAC energy consumption in commercial buildings)
- Liability and habitability standards, particularly in commercial leasing, where thermal comfort disputes can become contractual issues
In India, ASHRAE 55 is an American standard that many projects use as a comfort benchmark, often alongside local codes such as ECBC and the National Building Code. For the occupant side of the story, read our complete guide to thermal comfort in office buildings.
Where Radiant and Localized Comfort Technologies Fit In
Traditional HVAC systems are built to condition an entire volume of air to hit a single target temperature, which is a fairly blunt way to satisfy a standard built around six interacting variables. Technologies that address radiant temperature and localized comfort directly, rather than relying purely on air temperature, are often better positioned to meet the ASHRAE 55 comfort zone efficiently, particularly in spaces with high ceilings, variable occupancy or inconsistent air distribution, where the ASHRAE comfort zone is hardest to hold.
This is the design space Seisou Labs works in. The company’s ceiling-mounted thermal comfort panels are built to influence the radiant and localized comfort factors ASHRAE 55 accounts for, rather than simply conditioning an entire room’s air volume. It’s a meaningfully different approach from conventional air conditioning, and worth understanding on its own terms rather than as a variant of radiant cooling.
To see how this fits into the bigger picture, read our overview of green building technology in India and where thermal comfort innovation is headed next.
Learn more about Seisou SLOW →
Ready to Design for Real Comfort, Not Just Compliance?
Comfort that holds steady is a design problem, not a thermostat problem. Meeting ASHRAE 55 thermal comfort requirements on paper is one thing, delivering comfort occupants actually feel is another. Seisou SLOW is built to address the radiant and localized comfort factors that standard air conditioning often misses, keeping offices inside the comfort zone without cold drafts.
Frequently Asked Questions
What is ASHRAE Standard 55? ASHRAE Standard 55 (often searched as ASHRAE 55 thermal comfort) defines the combinations of environmental and personal factors, including temperature, humidity, air speed, clothing and activity level, that produce acceptable thermal comfort for most building occupants.
What is the ASHRAE thermal sensation scale? It is a seven-point scale from -3 (cold) to +3 (hot) used to describe how people feel, with 0 meaning neutral.
What PMV range does ASHRAE 55 recommend? Between -0.5 and +0.5 for typical mechanically conditioned spaces, which corresponds to roughly 10% of occupants being dissatisfied.
What is the difference between PMV and PPD? PMV predicts the average thermal sensation of occupants on a scale from cold to hot, while PPD estimates the percentage of occupants likely to be dissatisfied, even when the average PMV score looks acceptable.
What temperature range does ASHRAE 55 recommend for offices? There is no single number. The ASHRAE comfort zone depends on humidity, air speed, activity and clothing, so the thermal comfort range moves with them. Commonly cited summer ranges are roughly 23 to 26 degrees C, but check your own conditions with the CBE Thermal Comfort Tool.
How does the adaptive comfort model differ from the PMV/PPD model? The adaptive comfort model accounts for occupants adjusting their expectations and behaviour based on outdoor climate, generally allowing a wider acceptable temperature range in naturally ventilated buildings than in fully conditioned spaces.
Does ASHRAE 55 apply in India? ASHRAE 55 is an American standard that many Indian projects use as a comfort benchmark, often alongside local codes such as ECBC and the National Building Code.
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