Quick answer
Demand-controlled ventilation (DCV) is a control strategy that varies the amount of outdoor air an HVAC system brings into a space based on how many people are actually there, usually measured with carbon dioxide (CO₂) or occupancy sensors, instead of supplying the full design amount all the time.
Outdoor air must be heated, cooled and dried, so bringing in only what occupants need saves energy while keeping ventilation within the standard.
Quick facts
The key facts about Demand-Controlled Ventilation, with sources:
- Also called
- DCV, demand control ventilation
- Common sensing
- CO₂ sensors, occupancy sensors, people counters, schedules
- Ventilation standard
- ASHRAE 62.1-2025, which adds DCV control sequences 1
- Energy code link
- Commercial codes such as ASHRAE 90.1 require DCV in some high-occupancy spaces; check your edition 23
- Usually run by
- A building automation system or rooftop unit controller 4
- Where it helps most
- Spaces with large, changing occupancy: classrooms, gyms, auditoriums, meeting rooms
Key takeaways
- DCV brings in outdoor air in proportion to how many people are present.
- It saves the energy of heating, cooling and drying air nobody needs.
- CO₂ sensors are the most common way to estimate occupancy.
- ASHRAE 62.1-2025 adds DCV control sequences; commercial energy codes require DCV in some spaces 1 2.
- Bad sensor placement or drift can under-ventilate a room, so calibration and checks matter.
What DCV does
Ventilation standards set outdoor air rates per person and per square foot. Without DCV, a system brings in enough air for a full room every hour it runs, even when the room is half empty. That outdoor air has to be conditioned: heated in winter, cooled and dried in summer.
DCV trims the outdoor air when fewer people are present and raises it as the room fills. ASHRAE 62.1, the ventilation standard for commercial buildings, now in its 2025 edition, adds demand-control ventilation control sequences 1.
In homes, the idea shows up in simpler forms: ventilation fans on timers, humidity-controlled bath fans, or ERVs with boost modes. True CO₂-based DCV is mostly a commercial strategy.
Sources: [1]
How a CO₂-based DCV loop works
- People exhale CO₂ → room CO₂ rises above outdoor levels
- Sensor reports CO₂ → controller estimates occupancy
- Controller opens the outdoor air damper or speeds the ventilation fan
- Room CO₂ settles → damper eases back toward the minimum
- Building-area minimum outdoor air is always kept for non-occupant sources
Why CO₂ is used, and its limits
People are the main source of CO₂ indoors, so the difference between indoor and outdoor CO₂ tracks how many people are in a room and how much fresh air is reaching them. That makes CO₂ a handy, cheap proxy for occupancy.
It is only a proxy. CO₂ does not measure other pollutants such as VOCs from materials or particles from outdoors.
That is why ventilation standards keep a floor of outdoor air based on floor area, even when a room is empty.
CO₂ also lags: it takes time to build up after a room fills, so sequences must react quickly enough.
The two parts of a ventilation rate, and which one DCV changes
Commercial ventilation rates are built from two pieces. One part scales with people, because people give off CO₂, moisture and odors. The other part scales with floor area, because furniture, finishes and equipment give off pollutants whether or not anyone is there.
DCV adjusts only the people part. The area part stays on whenever the space is occupied or scheduled to be. That is why a well-set DCV system never closes the outdoor air damper fully during occupied hours, even in an empty room.
Getting that floor right is the single most important setting. Set it too low and the room is under-ventilated before people arrive; set it too high and most of the savings disappear.
Ways to sense demand
| Method | How it works | Strength | Weakness |
|---|---|---|---|
| CO₂ sensors | Indoor CO₂ vs outdoor tracks occupancy | Simple, widely used | Lags; needs calibration |
| Occupancy sensors | Motion or presence | Fast on/off | Does not count people |
| People counters | Doorway or camera counts | Direct count | Cost; privacy |
| Schedules | Time-of-day occupancy plans | No sensors | Misses real changes |
| Combined | Occupancy plus CO₂ | Fast and proportional | More setup |
DCV vs related ventilation terms
| Term | What it is | How it relates |
|---|---|---|
| Ventilation rate | Outdoor air per person or area | DCV varies it within the standard |
| Fresh air intake | Where outdoor air enters | The damper DCV controls |
| Building automation system | The control network | Usually runs the DCV sequence |
| Economizer | Uses cool outdoor air for free cooling | Can override DCV to bring in more air when beneficial |
| HRV / ERV | Recovers energy from exhaust | Cuts the cost of air DCV brings in |
Example: cooling load saved by DCV in a meeting room
A large meeting room is designed for 1,000 CFM of outdoor air at full occupancy. Over a typical summer afternoon it averages half full, so DCV supplies about 500 CFM (example figures).
Outdoor air is 95°F; supply air conditions it to 75°F. Sensible load ≈ 1.08 × CFM × temperature difference (a standard HVAC engineering approximation).
| Case | Math | Sensible load from outdoor air |
|---|---|---|
| Fixed design outdoor air | 1.08 × 1,000 × 20 | 21,600 BTU/h (1.8 tons) |
| DCV at half occupancy | 1.08 × 500 × 20 | 10,800 BTU/h (0.9 ton) |
| Saved while half full | 21,600 − 10,800 | 10,800 BTU/h, before counting moisture |
In humid weather the moisture in outdoor air adds a latent load on top, so the real saving is larger. The minimum area-based outdoor air stays in place. DOE reports that high-performance control in commercial buildings can cut HVAC energy by 30% 4; DCV is one of the sequences that delivers it.
Where DCV is used
- Classrooms, lecture halls and gyms.
- Auditoriums, theaters and places of worship.
- Conference and meeting rooms.
- Restaurants dining areas and retail with changing crowds.
- Rooftop units in small commercial buildings, often as a built-in option.
Benefits and trade-offs
Benefits
- Cuts heating, cooling and drying of unneeded outdoor air.
- Keeps ventilation tied to real occupancy.
- Can lower peak loads and equipment run time.
- Gives a record of room CO₂ for comfort reviews.
Trade-offs
- Sensors drift and need calibration.
- Poor sensor placement gives wrong readings.
- Adds controls complexity.
- Little benefit in spaces with steady occupancy.
Where DCV goes wrong
The most common failures are sensors out of calibration, sensors placed near doors, windows or supply diffusers, and minimum damper positions set wrong. PNNL notes that many buildings with control systems are not properly commissioned, operated or maintained 5; DCV sequences are no exception.
DCV also cannot help where occupancy is steady and close to design all day. In those spaces, energy recovery may be the better tool.
Sources: [5]
Cost drivers
Costs include sensors, controller programming, damper actuators or fan drives, commissioning and ongoing calibration. Adding DCV to an existing rooftop unit or BAS is often a controls job rather than new equipment.
HyreHVAC publishes no prices without enough dated quotes. Check commercial HVAC incentives for programs that fund controls.
How DCV is set up
- Identify spaces with large, changing occupancy.
- Set design outdoor air rates per person and per area from ASHRAE 62.1 or the local code 1.
- Place CO₂ or occupancy sensors in the breathing zone, away from doors and diffusers.
- Program the sequence: minimum area-based outdoor air, ramp with occupancy, maximum at design.
- Commission: test the sequence, verify damper or fan response, document setpoints.
- Calibrate sensors on the maker’s schedule.
Maintenance
- Check CO₂ sensor calibration per the maker’s schedule.
- Verify damper actuators move fully and match the control signal.
- Review trend data for rooms stuck at minimum or maximum.
- Clean outdoor air intakes and filters.
Warning signs
- Stuffy rooms or complaints of drowsiness during full meetings.
- CO₂ readings that never change: failed or mislocated sensor.
- Dampers stuck closed or fully open.
- High energy use in mild weather with dampers wide open.
- Call a controls contractor; do not disable ventilation to save energy.
Standards and codes
ASHRAE 62.1-2025 sets ventilation for commercial buildings and adds DCV control sequences 1. Commercial energy codes, such as ASHRAE 90.1 and the IECC, require DCV in certain high-occupancy spaces; thresholds depend on the edition adopted 2 3.
For homes, ASHRAE 62.2-2025 sets dwelling ventilation and adds an optional IAQ Procedure path 1.
Misconceptions
- Myth DCV means less fresh air.
- Reality It means the right amount for the people present, with a minimum always kept.
- Myth CO₂ is the pollutant being controlled.
- Reality It is a proxy for occupancy, not the main concern.
- Myth Set it and forget it.
- Reality Sensors drift; calibration and trend checks are needed.
- Myth DCV works in every room.
- Reality It pays off where occupancy changes a lot.
Climate and code vary
DCV saves the most where outdoor air is costly to condition: hot, humid summers as in Florida and Texas, or cold winters as in Ohio. Code requirements depend on the commercial energy code each state has adopted 3.
When DCV makes sense
Consider DCV for any commercial space whose head count swings widely during the day. If occupancy is steady, focus on energy recovery and good scheduling instead.
Next step: review your building’s control sequences with a controls contractor, and compare air quality options on indoor air quality services.
Questions about Demand-Controlled Ventilation
What is demand-controlled ventilation?
Demand-controlled ventilation is a control strategy that varies the outdoor air a building brings in based on how many people are present, usually measured with CO2 or occupancy sensors. It keeps ventilation tied to real use and cuts the energy spent conditioning unneeded outdoor air.
How does CO2-based DCV work?
People exhale CO2, so indoor CO2 rises as a room fills. A sensor reports the level, and the controller opens the outdoor air damper or speeds a ventilation fan to bring CO2 back down. A minimum amount of outdoor air is always kept for pollutants not tied to people.
Is DCV required by code?
Often, for certain commercial spaces. Commercial energy codes such as ASHRAE 90.1 and the IECC require DCV in some high-occupancy spaces, with thresholds that depend on the edition your state or city has adopted. ASHRAE 62.1-2025 adds DCV control sequences.
Where should CO2 sensors be placed?
In the breathing zone of the occupied space, away from doors, windows, supply diffusers and exhaust grilles that would skew readings. Some systems use a sensor in the return duct, which averages several rooms. Placement and calibration matter more than sensor count.
Does DCV hurt indoor air quality?
It should not when set up right. DCV keeps outdoor air at or above what occupants need and keeps an area-based minimum at all times. Problems come from drifted sensors, bad placement or wrong minimum settings, which is why commissioning and calibration matter.
Can homes use demand-controlled ventilation?
In simple forms. Humidity-controlled bath fans, ERVs with boost modes and ventilation fans on timers adjust airflow to need. Full CO2-based DCV is mainly used in commercial buildings with large, changing occupancy.
How much energy does DCV save?
It depends on how much occupancy varies and how costly outdoor air is to condition. In our example, a meeting room averaging half full cut its outdoor air cooling load in half while partly occupied. DOE reports high-performance control can cut commercial HVAC energy by 30% overall.
Do CO2 sensors need calibration?
Yes. Sensors drift over time, and a sensor reading too low can cause under-ventilation. Follow the maker’s calibration schedule, and check trends for sensors that never change or read far from neighbors.
What is the difference between DCV and an economizer?
DCV sets the minimum outdoor air to match occupancy. An economizer brings in extra outdoor air for free cooling when outdoor conditions are cool and dry enough. They work together: when the economizer is active, it can bring in more air than DCV alone would ask for.
Sources
- ASHRAE, Standards 62.1 and 62.2 (2025 editions), retrieved .
- ASHRAE, Standard 90.1 Energy Standard for Sites and Buildings Except Low-Rise Residential, retrieved .
- U.S. DOE, Building Energy Codes Program, retrieved .
- U.S. DOE Building Technologies Office, Building Controls, retrieved .
- PNNL, Building Re-Tuning, retrieved .
Expert review
Written by the HyreHVAC Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Standards and editions from ASHRAE pages; control savings from DOE BTO; operations findings from PNNL. Code DCV thresholds were not quoted because they vary by edition. The meeting-room example uses a standard air constant and labelled example airflows.
Suggest a correction. We fix errors and say what changed.