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.

What is Green Finance? And How it Can Benefit Your Business

Jennifer Crowley
Aug 2, 2023
3 min read

Updated: Jul 19, 2024

Leaf cutting growing from a pile of coins atop a wooden table — Green financing broadens access to environmentally-friendly goods and services for individuals and enterprises, equalizing the transition to a low-carbon society and resulting in more socially inclusive growth.

Green finance is a loan or investment that promotes environmentally-positive activities, such as purchasing ecologically-friendly goods and services or constructing green infrastructure. As the hazards connected to ecologically destructive products and services rise, green finance is becoming a mainstream phenomenon.

What is the Benefit of Green Financing?

Green financing broadens access to environmentally-friendly goods and services for individuals and enterprises, equalizing the transition to a low-carbon society and resulting in more socially inclusive growth. This results in a ‘great green multiplier’ effect in which both the economy and the environment gain, making it a win-win situation for everyone.

Environmental Impact

a. Climate Change Mitigation: Green financing plays a crucial role in funding projects that help mitigate climate change, such as renewable energy generation, energy-efficient technologies, and carbon capture and storage. By supporting these initiatives, green financing contributes to reducing greenhouse gas emissions and transitioning to a low-carbon economy.

b. Conservation of Natural Resources: Green financing supports projects aimed at preserving and restoring ecosystems, protecting biodiversity, and promoting sustainable agriculture and forestry. These initiatives help conserve natural resources, enhance biodiversity, and promote sustainable land and water management practices.

c. Transition to a Circular Economy: Green financing encourages projects that promote the principles of a circular economy, such as recycling, waste reduction, and sustainable production practices. This shift from a linear “take-make-dispose” model to a circular approach helps reduce resource consumption, minimize waste generation, and promote sustainable consumption patterns.

Economic Advantages

a. Market Opportunities: Green financing creates new market opportunities by supporting the development and deployment of clean technologies and sustainable infrastructure. This can drive economic growth, innovation, and competitiveness, particularly in sectors such as renewable energy, green construction, and sustainable transportation.

b. Risk Mitigation: Green financing can help mitigate financial risks associated with climate change, resource scarcity, and environmental regulations. By supporting projects that promote sustainability, financial institutions and investors can reduce exposure to stranded assets, regulatory penalties, and reputational risks.

c. Cost Savings: Green financing promotes energy efficiency and the use of renewable energy sources, leading to cost savings for businesses and households in the long run. Energy-efficient buildings, for example, have lower operating costs, reduced energy consumption, and increased asset value.

Social Implications

a. Job Creation: Green financing can stimulate the growth of green industries such as renewable energy, energy efficiency, and sustainable infrastructure. This can lead to the creation of new job opportunities, both directly and indirectly, contributing to economic development and reducing unemployment rates.

b. Health Benefits: Green financing promotes projects that aim to reduce pollution and improve environmental conditions. This can have positive effects on public health by decreasing air and water pollution, thereby reducing the incidence of respiratory and other environmentally-related diseases.

c. Community Development: Green financing supports projects that enhance community resilience, such as sustainable housing, clean transportation, and access to renewable energy. These initiatives can improve living conditions and promote social equity by providing affordable and sustainable solutions to communities, including those that are traditionally underserved.

Types of Green Financing

Now that we have an understanding of what green finance is, let’s explore its different types:

Green Mortgages

Lenders provide better terms to home purchasers of properties with a high environmental sustainability rating or if the buyer agrees to invest in enhancing the environmental performance of a property.

Green Loans

Green loans are used to support environmental initiatives such as household solar panels, electric automobiles, energy efficiency projects, and more.

Green Credit Cards

Often considered to be a type of credit card that donates a portion of your eligible purchases to an organization that invests in climate action and/or partners with carbon mitigation programs to help you reduce your carbon footprint.

Green credit cards such as Aspirations’ Zero card plant a tree every time a customer makes a purchase. They enable customers to direct their expenditure toward green finance to have a lasting environmental impact.

Green Banks

Green banks employ public funds to spur private investment in renewable energy and other environmentally friendly initiatives. According to a 2020 research, the number of green banks in the US increased from one to 20 between 2011 and 2020, investing $7 billion in renewable energy.

Green Bonds

Green bonds account for the vast bulk of green funding. They include bond investments, the earnings from which are used to support various green initiatives such as renewable energy, clean transportation, and conservation, among others.

Green Financing vs Sustainable Financing

Green finance is a loan or investment that promotes environmentally-positive activities, such as the purchase of ecologically-friendly goods and services or the construction of green infrastructure.

Sustainable finance is an improvement of green finance, aiming to increase long-term investments in sustainable economic activities and projects but also taking into consideration environmental, social and governance (ESG) issues and risks.

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