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

Written by

Published on

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

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.
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.
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.
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)

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.
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.
Cost Predictability & Maintenance Savings
- Less strain on HVAC equipment.
- Lower maintenance cost due to fewer introduced contaminants, less filter load, etc.
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.

Why HEPA Filters Matter in Wildfire Season

Jennifer Crowley
Jun 28, 2024
4 min read

Updated: Jul 8, 2024

Firefighters working on a steep ravine to try and extinguish wildfires — As wildfire seasons become increasingly severe, HEPA filters play a crucial role in maintaining clean indoor air quality and protecting health.

As wildfire seasons grow longer and more intense, especially in regions like Canada and the western United States, maintaining clean indoor air quality has never been more important. At Blade Air, we understand the critical role that HEPA (High-Efficiency Particulate Air) filters play in protecting both residential and commercial indoor environments from the harmful effects of wildfire smoke. This guide explores why HEPA filters are essential during wildfire season and how they can make a significant difference in your air quality and overall health.

Hazy view of wildfire haze across a city scape as seen by two masked individuals on a balcony — The most harmful components of wildfire smoke are particulate matter (PM), since they can penetrate deep into the lungs, enter the bloodstream and lead to various health issues.

The Importance of Air Quality During Wildfire Season

Wildfire smoke is a complex mixture of gases and fine particles from burning vegetation, building materials, and other substances. The most harmful components of wildfire smoke are particulate matter (PM), especially PM2.5 (particles smaller than 2.5 micrometres). These microscopic particles can penetrate deep into the lungs and even enter the bloodstream, leading to various health issues:

Respiratory Problems: Persistent coughing, wheezing, and shortness of breath.
Aggravation of Asthma and COPD: Increased frequency and severity of attacks.
Cardiovascular Issues: Heart attacks and strokes.
Eye, Nose, and Throat Irritation: Immediate discomfort and potential long-term damage.
Long-term Health Impacts: Lung cancer and complications in vulnerable populations, such as children and pregnant women.

Understanding these risks underscores the critical need for effective air filtration during wildfire season. HEPA filters are designed to capture these dangerous particles, making them indispensable in safeguarding indoor air quality.

Blade Air HEPA Air Purifier — HEPA's superior performance lies in their ability to trap particles as small as 0.3 micrometres with at least 99.97% efficiency.

What is a HEPA Filter?

A HEPA filter is a type of mechanical air filter that forces air through a fine mesh, capturing harmful particles such as dust, pollen, smoke, and bacteria. To be classified as a true HEPA filter, it must meet stringent standards set by the United States Department of Energy (DOE) and effectively remove at least 99.97% of airborne particles as small as 0.3 micrometres (µm).

HEPA Filters: Essential in Wildfire Season

HEPA filters offer multiple benefits that are particularly crucial during wildfire season:

Superior Filtration Efficiency

HEPA filters are renowned for their ability to capture very fine particles, including those found in wildfire smoke. The key to their superior performance lies in their ability to trap particles that are as small as 0.3 micrometres with an efficiency rate of at least 99.97%. This ensures that even the smallest and most harmful particles are removed from the air:

Effective Against PM2.5: Given that PM2.5 is the most dangerous component of wildfire smoke, HEPA filters are highly effective in providing protection.
Captures a Range of Pollutants: In addition to smoke particles, HEPA filters also capture other pollutants such as pollen, dust mites, and pet dander.

Health Benefits

The health benefits of using HEPA filters during wildfire season are significant:

Reduces Respiratory Symptoms: People with allergies, asthma, and other respiratory conditions experience fewer symptoms.
Decreases Cardiovascular Risks: Lower exposure to airborne particles reduces the risk of heart attacks and strokes.
Improves Overall Well-being: Cleaner air contributes to better sleep, productivity, and mental clarity.

Reinforcing HEPA Filters with Activated Carbon

Many HEPA air purifiers also include activated carbon filters. While HEPA filters are designed to capture particles, activated carbon filters are effective at removing gases and odours such as volatile organic compounds (VOCs) that are released during wildfires. This combination of filters provides comprehensive air cleaning:

Odour Removal: Activated carbon filters eliminate the smoky smell associated with wildfires.
Chemical Filtration: They remove harmful chemicals such as benzene and formaldehyde.

How to Choose the Right HEPA Air Purifier

When selecting a HEPA air purifier, consider the following factors to ensure you are getting the most effective protection during wildfire season:

True HEPA Certification: Ensure the air purifier uses a true HEPA filter, meeting DOE standards for filtration efficiency.
Clean Air Delivery Rate (CADR): Look for a high CADR rating for smoke. This measures the air purifier’s efficiency in cleaning air.
Coverage Area: Match the air purifier’s coverage capacity (in square feet) to the size of your room or home area.
Filter Longevity and Ease of Replacement: Consider the lifespan of the filters and their ease and cost of replacement.
Noise Levels and Energy Efficiency: Choose a model that operates quietly and efficiently.

Using HEPA Filters: Best Practices

Illustrated image of an air purifier placed on a central location showcasing its air circulation capabilities — Strategic placement is important. Place the air purifier in the room where you spend the most time. For homes, this is often the bedroom or living room with a clear path for air to flow.

To maximize the effectiveness of HEPA air purifiers, follow these best practices:

Strategic Placement: Place the air purifier in the room where you spend the most time. For homes, this is often the bedroom or living room.
Continuous Operation: Keep the air purifier running 24/7 during wildfire season to maintain clean air.
Regular Maintenance: Replace HEPA and activated carbon filters according to the manufacturer’s recommendations to ensure optimal performance.
Seal Your Home: Use weatherstripping, door sweeps, and other measures to prevent outdoor air from entering your home. This reduces the burden on your air purifier.
Create a Clean Air Room: Designate a specific room with minimal outdoor air infiltration and use a high-efficiency air purifier to maintain air quality.

Blade Air: Your Partner for Clean Air

At Blade Air, we are dedicated to providing advanced air purification solutions that meet the highest standards of performance and reliability. Our flagship products, such as the HCFM-1 Portable HEPA Purifier, Pro Filter with Advanced Electromagnetic Filtration, and HEPA+ Filter, offer unmatched protection against wildfire smoke and other airborne contaminants.

Advantages of Blade Air HEPA Air Purifiers:

High-Efficiency Filtration: Our true HEPA filters effectively capture 99.99% of particles at 0.3 micrometres.
Comprehensive Coverage: Suitable for both residential and commercial spaces, providing wide-ranging protection.

As wildfire seasons become increasingly severe, HEPA filters play a crucial role in maintaining clean indoor air quality and protecting health. By investing in high-quality air purification systems and following best practices, you can significantly reduce exposure to harmful pollutants and ensure a healthier environment for yourself and your loved ones.

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