PMV stands for Predicted Mean Vote, a numerical index used in building design and HVAC engineering to predict how warm or cool a group of people will feel in a given indoor environment. The scale runs from -3 (cold) to +3 (hot), with 0 representing thermal neutrality, the point where most people feel neither too warm nor too cold. It’s the most widely used thermal comfort model in the world, embedded in international building standards that shape how offices, hospitals, schools, and homes are heated and cooled.
PMV can also refer to pigeon paramyxovirus in veterinary contexts or polymorphic ventricular tachycardia in cardiology, but the thermal comfort meaning is by far the most common usage. This article focuses primarily on the thermal comfort index.
How the PMV Scale Works
The PMV model was created by Danish researcher P.O. Fanger in the late 1960s after extensive experiments in climate chambers where subjects rated how they felt under controlled conditions. Fanger translated those subjective ratings into a mathematical model that predicts the average thermal sensation of a large group of people. The seven-point scale looks like this:
- -3: Cold
- -2: Cool
- -1: Slightly cool
- 0: Neutral (ideal)
- +1: Slightly warm
- +2: Warm
- +3: Hot
A PMV of 0 doesn’t mean every single person is perfectly comfortable. It means that, on average, the group reports neutral thermal sensation. Even under ideal conditions, roughly 5% of people will feel dissatisfied. That’s why PMV is often paired with a second metric called PPD (Predicted Percentage Dissatisfied), which estimates what fraction of occupants will find the environment too warm or too cold.
The Six Factors in a PMV Calculation
The model accounts for six variables: four related to the environment and two related to the person. On the environmental side, it factors in air temperature, radiant temperature (heat radiating from walls, windows, and equipment), air speed, and humidity. On the personal side, it considers metabolic rate and clothing insulation.
Metabolic rate is measured in “met” units. Sitting relaxed produces about 1.0 met (58 watts per square meter of body surface), while sedentary office work like typing runs closer to 1.2 met (70 W/m²). Standing and walking increase the rate significantly, with a brisk walk at 5 km/h generating about 3.4 met. For a typical office worker, the range is narrow, roughly 1.0 to 1.5 met, so engineers often use a middle value around 1.25 met for simplicity.
Clothing insulation is measured in “clo” units. A T-shirt adds about 0.09 clo, a long-sleeve shirt around 0.25 clo, and a full business outfit with trousers and jacket can reach 1.0 clo or higher. Summer clothing typically falls between 0.5 and 0.7 clo, while winter office attire sits closer to 1.0 clo. These values matter because they determine how much body heat you retain versus release to the surrounding air.
What Building Standards Require
ASHRAE Standard 55, the dominant thermal comfort standard in the United States, defines the comfort zone as a PMV between -0.5 and +0.5. Any hour where the PMV falls outside that range counts as a “discomfort hour.” On a psychrometric chart (the kind HVAC engineers use to visualize temperature and humidity together), this comfort zone translates to a temperature range of about 3 to 5°C (5 to 8°F) depending on clothing level and humidity.
The ISO 7730 standard, used internationally, takes a similar approach but defines three comfort categories. Category A requires PMV between -0.2 and +0.2, Category B allows -0.5 to +0.5, and Category C extends to -0.7 to +0.7. Higher-end buildings like hospitals or executive offices typically aim for Category A, while general office space targets Category B.
Where the PMV Model Falls Short
The PMV model works well in air-conditioned buildings where temperature and humidity are tightly controlled. In naturally ventilated buildings, where people can open windows and adjust to seasonal shifts, it performs poorly. The model consistently overestimates how uncomfortable people feel in warm conditions. In practice, people in naturally ventilated spaces tolerate a wider range of temperatures than PMV predicts, likely because they’ve adapted psychologically and behaviorally to their environment. They expect some variation, dress accordingly, and use fans or open windows to compensate.
This mismatch led to the development of adaptive comfort models, which base acceptable temperatures on outdoor conditions rather than a fixed calculation. The adaptive approach recognizes that someone living through a hot summer in a building without central air conditioning will feel comfortable at temperatures that the PMV model would flag as too warm. Modern standards now include both approaches: PMV for mechanically cooled buildings and adaptive models for naturally ventilated ones.
Another limitation is that the PMV model was developed primarily from data collected in climate chambers with young, healthy Western subjects. Its accuracy varies across different populations, age groups, and climates. Research consistently shows that the model’s simplistic treatment of sweating contributes to errors in warm environments, where it underestimates the body’s ability to cool itself through perspiration.
How PMV Is Used in Practice
Building engineers use PMV during the design phase to size HVAC systems and set temperature targets. Energy simulation software calculates PMV values hour by hour across an entire year, flagging periods where the building would fall outside the comfort zone. The goal is to minimize discomfort hours while keeping energy use reasonable.
PMV also shows up in green building certification systems like LEED, where maintaining thermal comfort earns credits. Some modern buildings use real-time PMV calculations tied to sensors that measure temperature, humidity, and air speed, adjusting the HVAC system dynamically to keep the index near zero. Wearable sensors and occupancy detection are increasingly being tested to refine the personal side of the equation, estimating clothing and activity levels more accurately than fixed assumptions.
Other Meanings of PMV
Pigeon Paramyxovirus (PMV-1)
In veterinary medicine, PMV-1 refers to a viral infection in pigeons caused by avian paramyxovirus type 1. Infected birds show distinctive neurological symptoms: head tremors, twisted necks (torticollis), poor balance, inability to fly, and persistent diarrhea that doesn’t respond to treatment. They also drink excessively. The virus causes kidney inflammation, liver damage, and brain inflammation. PMV-1 is a significant concern for racing pigeon keepers and can spread rapidly through flocks.
Polymorphic Ventricular Tachycardia (PMVT)
In cardiology, PMVT describes an abnormal heart rhythm originating in the lower chambers of the heart. Its defining feature is a continuously changing electrical pattern on an ECG, unlike typical ventricular tachycardia where the pattern stays consistent. PMVT results from abnormal electrical recovery in heart cells, creating chaotic signaling. It is mechanistically distinct from ventricular fibrillation, though both are dangerous rhythms that require urgent treatment.