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

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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.

The Importance of Indoor Air Quality in Older Buildings

Jennifer Crowley
Jul 4, 2024
5 min read

Updated: Jul 8, 2024

Older building rooftop ventilation — Older buildings often face several air quality challenges due to years of accumulated wear and tear and outdated construction practices.

Indoor air quality (IAQ) is a critical aspect of building management that directly affects the health and well-being of occupants. This importance is magnified in older buildings, where outdated infrastructure, prolonged wear and tear, and the presence of potentially hazardous materials can significantly compromise air quality.

For building owners and facility managers, ensuring good air quality in older buildings is not just a matter of comfort; it is essential for maintaining the health and safety of those who live and work in these environments. Poor IAQ in such buildings can lead to various health issues, decreased productivity, and non-compliance with modern regulatory standards, making it a fundamental concern that demands urgent action.

Common Air Quality Issues in Older Buildings

Older buildings often face several air quality challenges due to years of accumulated wear and tear and outdated construction practices. These issues can severely impact IAQ, making it crucial to identify and address them to ensure a healthy living and working environment. Common air quality problems in older buildings include:

Mold and Mildew: Due to water damage or high humidity, mold and mildew can thrive in older buildings, releasing spores into the air.
Dust and Allergens: Accumulated dust and debris in older buildings can harbor allergens, worsening respiratory conditions.
Outdated HVAC Systems: Inefficient and outdated HVAC systems may not adequately filter air, leading to the circulation of pollutants.
Asbestos and Lead: Many older buildings still contain asbestos and lead-based materials, which can pose serious health risks if disturbed.
Chemical Pollutants: Use of old construction materials and maintenance products can introduce volatile organic compounds (VOCs) into the indoor environment.

Health Impacts

Young multi-racial woman clutching her chest and coughing while attempting to use a rescue inhaler — Exposure to contaminants seen in older buildings can result in many adverse health effects.

The poor indoor air quality in older buildings can lead to numerous health problems for occupants, emphasizing the need for immediate attention. Exposure to contaminants commonly found in older buildings can result in a range of adverse health effects, including:

Respiratory Issues: Exposure to mold spores, dust, and other airborne pollutants can exacerbate asthma, bronchitis, and other respiratory conditions.
Allergies: Increased levels of allergens such as dust mites and pollen can trigger allergic reactions, leading to discomfort and reduced quality of life.
Productivity Loss: Poor air quality can cause headaches, fatigue, and difficulty concentrating, reducing productivity and overall well-being.
Long-Term Health Risks: Chronic exposure to pollutants like asbestos and lead can lead to severe health conditions, including cancer and neurological disorders.

Regulatory Concerns in Older Buildings

Ensuring compliance with air quality standards and regulations is critical for older buildings, as failing to meet these requirements can lead to significant health risks and legal issues. Both Canada and the US have established stringent guidelines to protect indoor air quality, but older buildings often struggle to meet these standards due to several factors:

Canadian Regulations:

Health Canada: Sets IAQ guidelines that include maximum acceptable concentrations for common indoor pollutants such as carbon monoxide, formaldehyde, and mold spores. Older buildings might not have adequate ventilation systems to meet these guidelines.
National Building Code of Canada: Requires proper ventilation and air filtration systems to maintain acceptable IAQ. Many older buildings were constructed before these codes were established, leading to inadequate ventilation and outdated HVAC systems.
Provincial Regulations: Provinces like Ontario have specific requirements under the Ontario Building Code, focusing on ventilation and mold prevention. Older buildings often lack the modern infrastructure necessary to comply with these regulations. The Canadian Centre for Occupation Health and Safety provides a great resource to link to provincial guidance.
See also ASHRAE Standards below

United States Regulations:

Environmental Protection Agency (EPA): Establishes IAQ guidelines and provides resources for maintaining healthy air in buildings. The EPA’s standards include acceptable levels for various indoor pollutants. Older buildings often have outdated or poorly maintained HVAC systems that fail to filter out pollutants effectively.
Occupational Safety and Health Administration (OSHA): Mandates safe working conditions, including standards for indoor air quality in workplaces. Older buildings may not meet these standards due to deteriorating infrastructure and lack of modern air purification systems.
ASHRAE Standards: The American Society of Heating, Refrigerating, and Air-Conditioning Engineers sets voluntary IAQ standards that are widely adopted, covering ventilation rates and air filtration. Older buildings may not have been designed to meet these standards, resulting in subpar IAQ.

Older buildings often fail to meet these standards due to outdated infrastructure and lack of modern air filtration systems, which can result in regulatory fines and increased health risks for occupants. Additionally, many of these buildings were constructed before current IAQ standards were established, making retrofitting necessary but often challenging and costly.

Indoor Air Quality in Older Buildings Case Study

Distillery District Project Design image — Click on the image to watch a video version of the full Distillery District Case Study

Toronto Distillery District Energy Efficiency & IAQ Project

The Historic Gooderham & Worts Distillery District, opened in 2003, is widely regarded as Ontario's premier arts, culture, and entertainment destination, and one of its hottest tourist attractions. This internationally acclaimed village features brick-lined streets and 47 vibrantly restored 19th-century Victorian industrial buildings. As a major dining, shopping, and cultural hub in Toronto, Canada, the importance of maintaining and upgrading these historic buildings to achieve better indoor air quality (IAQ) is paramount.

Blade Air Electromagnetic Pro Filter — Blade Air Pro Filters capture particles 40 times smaller than traditional filters.

In December 2021, the Distillery District management team sought Blade Air's help to improve IAQ without the high costs and energy demands of HEPA or UV solutions. They needed an efficient, cost-effective solution to enhance air quality while reducing their carbon footprint.

Blade Air recommended their Pro Filter electromagnetic filters, which outperform HEPA filters in capturing particulate matter and inactivating viruses, with significantly lower energy requirements. The Distillery District conducted trials in two buildings, resulting in impressive outcomes:

Energy Savings: Up to 75% reduction in fan motor consumption.
Improved Filtration: 2.25 times better performance in capturing and removing bacteria from the airstream compared to MERV-13 filters.
Enhanced Air Quality: Significant improvement in indoor air quality, creating a healthier environment for occupants.
Cost-Effective Solution: Achieved high efficiency and superior air quality without the prohibitive costs of HEPA or UV solutions.

Upgrading these historic buildings with modern air quality solutions ensures they continue to be a safe, healthy, and attractive destination for visitors and tenants alike. Click here to read the full Case Study.

Blade Air IAQ Solutions

For building owners and facility managers, addressing IAQ is not just a regulatory requirement but a fundamental concern that directly impacts the health and satisfaction of occupants. The adverse effects of poor air quality, from respiratory issues to productivity loss, highlight the need for immediate action.

Blade Air is Your Trusted Partner in IAQ for Older Buildings.

By implementing Blade Air’s solutions, you can ensure your building meets and exceeds current air quality standards, safeguarding health, avoiding potential legal and financial repercussions, and creating safer, healthier environments for everyone.

Blade Air is dedicated to providing expert guidance and retrofitting services to help you achieve these goals. Contact Blade Air today to learn how we can help transform the air quality in your building, ensuring a healthier and more comfortable environment for all occupants.

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