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When More Ventilation Isn’t Always Better: The Emerging Case for Outside Air Reduction

Learn why outside air reduction is reshaping building operations. Balance indoor air quality, energy savings, and ASHRAE standards in the post-COVID era.

Ava Montini

Sep 12, 2025

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At the height of the COVID-19 pandemic, building operators were given one clear directive: get as much fresh outside air into the building as possible.


The reasoning was simple and sound: diluting indoor air with outside air reduced the concentration of airborne viruses and gave occupants a greater sense of safety. Schools cranked open dampers, office towers increased their minimum ventilation rates, and healthcare facilities invested heavily in boosting air exchanges.


That strategy worked in an emergency, but it also came at a cost. Energy bills spiked as HVAC systems struggled to heat and cool the constant flow of unconditioned outside air. Humidity control became more difficult. Comfort complaints rose. And in some regions, the “fresh air” being drawn inside was anything but fresh. Things like wildfire smoke, traffic emissions, and industrial pollutants all found their way indoors.


Fast forward to today, and the conversation has shifted. ASHRAE and other standard-setting bodies have recognized that the blanket approach of maximum ventilation isn’t sustainable as a long-term practice.


As we’ve moved past the emergency phase, a more nuanced picture is emerging. Outside air confers benefits (especially in terms of health), but it also imposes costs: energy, comfort, mechanical wear, sometimes even polluted air if your outdoor environment isn’t clean. ASHRAE, energy codes, and HVAC practice are now pushing toward finding balance. One big part of that shift is outside air reduction (or controlling outside air to what’s necessary, rather than “as much as possible”).


Why Reduce Outside Air? What Are the Trade-Offs


To see why reducing outside air is resurfacing, it's helpful to walk through what the costs are and what the benefits might be of dialling things back.



The Costs of Too Much Outside Air

  1. Energy Use

    • Heating and cooling costs skyrocket when you have to condition large volumes of outdoor air, especially in extreme climates. In summer, bringing in hot, humid air means your cooling system works harder; in winter, cold air needs heating.

    • Beyond simply heating/cooling, there’s also fan energy. More outside air often means more airflow through dampers, larger pressure differentials, etc.

  2. Visual Comfort / Thermal Discomfort

    • Cold drafts in winter; humid, sweaty feelings in summer if moist outdoor air isn’t adequately dehumidified.

    • Inconsistent thermal zones due to mixing outside air with return or recirculated air.

  3. Mechanical Wear & Maintenance

    • Outside air includes particulates, pollutants, and moisture. Therefore filters, coils, ducts, and dampers need more maintenance.

    • When outside air brings in pollutants or high humidity, it can cause corrosion, mold, or damage to finish materials.

  4. Indoor Air Quality Considerations

    • Ironically, bringing in outside air isn’t always “cleaner”; if outdoor air is polluted (e.g. wildfire smoke, high PM2.5, industrial pollution), ventilation could degrade indoor air quality.


The Benefits of Reducing Outside Air (When Done Right)

  1. Energy Savings

    • Reduced heating/cooling loads → lower utility bills.

    • In some ASHRAE Standard 90.1 addenda / code changes, reducing outdoor air intake is explicitly a path toward improved energy efficiency. For example, changes made in standard 90.1-2019 (and later) allow reduced outside air intake in central systems and reduced minimum flows in VAV (variable air volume) boxes. Energy Codes

    • Buildings with moderated outside air approaches (versus maximum outside air strategy) can often hit much better energy performance, especially in climates with extreme temperatures.

  2. Comfort and Building Stability

    • More stable indoor temperatures, less risk of humidity spikes or condensation issues.

    • Better ability to maintain indoor comfort metrics, which improves occupant satisfaction.

  3. Cost Predictability & Maintenance Savings

    • Less strain on HVAC equipment.

    • Lower maintenance cost due to fewer introduced contaminants, less filter load, etc.

  4. Health / IAQ Still Possible

    • By using strategies such as proper filtration (appropriately rated filters), UVGI, good air distribution, and periodic flushing, you can maintain healthy indoor air even with more controlled outside air.

    • ASHRAE guidance, post-COVID, suggests that ventilation + filtration + other engineering controls together are the path—not merely “open all dampers.” ASHRAE


How ASHRAE & Codes Are Shifting



The push to balance ventilation, energy and comfort is finding formal expression in updated standards and codes. Some key threads:

  • ASHRAE Standard 62.1 (Ventilation for Acceptable Indoor Air Quality) has been the go-to for minimum ventilation. But recent addenda adjust how outside air rates are calculated, especially in Variable Air Volume (VAV) systems, enabling more dynamic or performance-based approaches. Energy Codes

  • ASHRAE Standard 90.1 (Energy Standard for Buildings Except Low-Rise Residential Buildings) is increasingly recognizing that “more outside air” is not always the optimal path for energy efficiency. The 2019 to 2022 versions include addenda that allow for reduced outdoor air intake in some scenarios and model outside air intake more precisely. Energy Codes

  • Post-COVID Guidance from the Epidemic Task Force and other committees acknowledges that increased ventilation is helpful for infectious disease mitigation—but also warns about the cost, feasibility, and trade-offs. ASHRAE’s filtration & disinfection guidance, for instance, emphasizes that filters should be sealed well, systems should be maintained, and energy impacts considered. ASHRAE

  • There is growing interest in “ventilation efficiency” (i.e. how well the outdoor air being brought in actually participates in diluting contaminant levels) vs simply “bringing in more air.” That opens doors for smarter design: placement of supply/exhaust, air distribution patterns, possibly recirculation with clean filtration, and technology like UVGI in ducts. arXiv


What Building Owners / Managers Should Do

If you’re in charge of managing indoor air quality, HVAC systems, or the budget, here are some practical steps, questions, and strategies to move toward smart outside air reduction without compromising health or compliance.

Step

What to Do

Key Questions & Considerations

1. Audit your current system

Measure how much outside air is being brought in currently. Identify how often dampers are fully open, what settings for minimum outside air are. Document past energy bills, thermal comfort complaints.

Do you really need to run at 100 % outdoor air all the time? What’s the outside-air fraction during non-peak periods? How often are you using demand-controlled ventilation?

2. Model / simulate

Use energy modelling (or vendor/engineering consultants) to simulate what energy & comfort impact you’d see from reducing outside air to code minimum vs current levels vs maximum “pandemic level.” Include local climate, outdoor pollutant levels.

What’s your climate? How extreme are winters / summers? What are outdoor pollution or humidity challenges? Can your HVAC system handle variable loads well?

3. Filter & clean

If you reduce outside air, you’re inherently relying more on “recirculation / indoor air cleaning” to maintain IAQ. Ensure your filters are appropriate efficiency, well sealed, replaced regularly. Consider supplementary measures (UV, air cleaners, HEPA, etc.).

What is the MERV rating you’re using? Can your fan/coil handle higher efficiencies without losing capacity? How about maintenance cycles?

4. Design flexibility & control

Make systems adjustable—both in terms of outdoor air intake (dampers, controls) and monitoring (CO₂, PM2.5, VOCs). This allows ramping up when needed, and reducing when risk is low or when conditions are unfavorable.

Do you have sensors to detect indoor air quality? Do your controls allow override or programmed changes? Are occupants/management aware and aligned with policy?

5. Engage stakeholders

Staff, occupants, board members often worry that reducing outside air means compromising health. Transparency helps: show them energy/comfort data, IAQ readings, trade-offs. Sometimes policies (e.g. open windows during good outdoor air, closed when it’s bad) help.

What are occupant expectations? Do you have health policies in place? Who signs off on trade-offs (e.g. budget vs comfort)?

6. Monitor & adjust

After changes, monitor indoor environment (temperature, humidity, CO₂, pollutant levels), energy, comfort complaints. Be ready to adjust. Outside air isn’t a static setting; it’s dynamic.

How often will you review? What thresholds trigger change? For example: high CO₂ or PM2.5, or outdoor air pollution alerts, might warrant reducing outside air.


What This Means for Policy, Standards, & the Future



Energy codes & carbon targets

As jurisdictions push toward net zero or carbon reduction, the HVAC energy penalty of over-ventilating becomes a liability. Efficient outdoor air management helps reduce energy use, which helps reduce emissions. ASHRAE 90.1’s newer addenda are already projecting energy savings from smarter outside air settings. Energy Codes


Health & resilience

Pandemics have taught us that buildings need flexibility—not fixed, extreme settings. Systems that can adapt: e.g., crank up ventilation when risk is high, pull back otherwise—are more resilient. Outdoor air reduction is part of enabling that flexibility.


Indoor air quality (IAQ) & occupant wellness

People increasingly expect buildings (schools, offices, public spaces) to deliver both clean air and comfort without extreme energy waste. Outside air reduction done thoughtfully helps spread the benefits: lower energy bills, better comfort, less waste.


Cost pressures

Energy costs are volatile. Running massive outside air loads just to “play it safe” all the time may no longer be financially justified, especially in regions with high energy costs or challenging climates.


Getting Outside Air Right, Not Just More


After so many years where the message was “more outside air, more safety,” we’re entering a more mature phase—one where how outside air is managed, rather than just how much, becomes the critical question.


Reducing outside air (when it can be done safely) doesn’t mean lowering standards or compromising on health. It means using all the tools: ventilation, filtration, controls and monitoring, to deliver indoor air quality that is healthy, comfortable, sustainable and cost-effective.


If you’re managing buildings, this is the moment to rethink your default settings. Push for audits, invest in systems and sensors, communicate clearly with occupants. Because the buildings that get this right will be healthier, more resilient, and much more efficient in the long run.



How Peak Demand Shapes Building Costs, Emissions, and Operations

  • Writer: Ava Montini
    Ava Montini
  • Jul 15
  • 5 min read

By mid-July, the weather forecast stops being small talk. It becomes operational.


With heat domes intensifying across North America and grid operators issuing near-daily alerts, facility and portfolio managers are paying closer attention and for good reason.


Ontario’s IESO issued more peak warnings before August than in the entire 2022 season. In 2024, Texas broke its own energy demand record 10 times. According to the U.S. Energy Information Administration, commercial buildings in the U.S. now consume around 35% of the nation’s electricity, making this sector a key player in shaping grid performance during high-load periods.


Energy usage is showing up beyond the utility bill; in Scope 2 emissions disclosures, tenant expectations, and stakeholder audits. With grid volatility rising and energy performance now directly tied to financial exposure and emissions visibility, organizations are starting to reassess how energy decisions are made, tracked, and reported.


Energy, increasingly, is functioning as a real-time indicator of how integrated and responsive a business truly is.


Energy Has Left the Boiler Room

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By now, it is well known in commercial real estate that energy data now reaches beyond utility bills. It now plays a role in broader business decisions, even if that shift has happened gradually.


According to CBRE’s 2024 Global Investor Intentions Survey, 59% of respondents now factor sustainability-linked performance into their investment evaluations. Energy efficiency specifically was cited as a way to protect long-term value, something increasingly relevant as operating costs and emissions reporting become more closely tied.


This kind of performance data doesn’t just stay within the engineering team. It’s showing up in investor due diligence, influencing lease terms, and being used to support eligibility for green financing or incentive programs.


What also matters is how efficiency is tracked, shared, and applied to meet business goals. Consistent performance during peak periods, clear Scope 2 reporting, and reliable internal coordination are becoming expected, especially in markets under regulatory or stakeholder pressure.


These are no longer emerging trends. They’re baseline expectations for any organization managing significant energy loads.


A Few Hours Can Shape Your Annual Energy Spend


Many commercial buildings are billed not just for how much energy they use, but when they use it.


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In most North American markets, utilities and grid operators apply what's called "peak demand pricing," a system that looks at a facility’s electricity use during the most critical periods on the grid, typically when demand is at its highest and supply is tightest. These peak periods often occur during extreme heat events or late afternoons in the summer.


Utilities use these moments to assess each building’s contribution to overall grid stress. That data is then used to determine a portion of the facility’s charges for the following year, often under separate line items like demand charges, capacity tags, or grid contribution fees.


In Ontario, for instance, a commercial building’s Global Adjustment (GA) charges are based on its electricity load during the five highest one-hour demand periods between May and October. These hours aren’t announced in advance, but are predicted with some accuracy by monitoring weather and grid forecasts. The IESO uses this data to assign an "ICAP tag," which influences your facility’s GA cost over the next billing cycle.


In the U.S., several regional transmission organizations (RTOs) such as PJM, ISO-NE, ERCOT, and NYISO use similar methods. ERCOT’s 4CP (Four Coincident Peaks), for example, calculates charges based on your facility’s usage during four peak hours—each occurring on the highest-demand day in June, July, August, and September.


These billing models are especially impactful in sectors with high energy intensity or round-the-clock operations: healthcare, food storage, manufacturing, data centers. In these cases, those few hours can account for 30% to 70% of the annual electricity bill, depending on rate structure and local regulations.


Unlike fixed charges, these costs can be actively managed. Facilities that have visibility into upcoming peak periods and a plan to temporarily reduce load—even by 5% to 10%—can significantly cut future costs and improve their carbon reporting by reducing emissions during grid-critical periods.


Grid Strain Is Becoming More Common


During 2024, regional electricity demand hit new highs across North America, and the pace is changing how energy is managed today.


In Texas, ERCOT reached a record 85,931 MW of demand on August 20, 2024, surpassing its previous all-time high set the year before. This surge wasn’t a one-off. In May 2025, ERCOT warned that demand might exceed 84,000 MW, potentially challenging the previous May record of 77,000 MW. These numbers reflect rising load from data centers, EV charging, and increased AC usage, raising the stakes for flexibility in facility operations.


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In Ontario, 2024 brought a similar trend. Warmer-than-usual summer temperatures led to 277 peak hours above 20,500 MW demand. Double the 138 hours seen in 2023. Meanwhile, refurbishments at nuclear plants and reduced imports forced the grid to rely more on gas generation. These factors have introduced more volatility into rate structures and heightened the risk for assets that lack demand-side flexibility.


July Offers a Useful Midpoint for Evaluation

By this stage in the summer, most large energy users have had at least one or two opportunities to respond to a peak event. This creates a natural checkpoint.


  • Was your team prepared?

  • Did the systems respond as expected?

  • Were load reduction strategies discussed across departments, or handled in isolation?


Demand charges alone can represent 30–70% of a commercial customer’s total electricity costs, and adopting time-based rate strategies has enabled many to reduce peak usage by around 16% on average, sometimes reaching up to 40% 


Performance Is Increasingly Measured in Real Time

As ESG reporting becomes more sophisticated, energy data is being tracked and evaluated at a finer level of detail. The Greenhouse Gas Protocol now encourages organizations to report Scope 2 emissions using time-based methods that reflect when electricity is consumed and how carbon-intensive the grid is at that hour.


Temporary spikes during peak demand periods can now influence not just emissions totals, but also eligibility for incentive programs and performance-based certifications. LEED and ENERGY STAR, for example, have begun placing more emphasis on interval data and how buildings perform under real operating conditions.


For property managers and sustainability leads, being able to show avoided demand during grid-stressed hours adds credibility to reporting.



As the second half of summer unfolds, the patterns emerging now, how buildings respond, how teams coordinate, and how data is tracked, will quietly shape the months ahead. Even without sweeping changes, the season offers a chance to observe, adjust, and carry forward what proves useful.


Energy may be a technical input, but increasingly, it reflects how an organization works under pressure and where it’s headed next.


Explore expert insights, stay up to date with industry events, and gain a deeper understanding of the cutting-edge developments that are revolutionizing the indoor air quality landscape within Blade Air's comprehensive Insights Hub.

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