Radon Mitigation in Tight Homes: Why Every Mitigator Must Understand ASHRAE 62.2
As a radon mitigator, you are a health and safety professional. Your primary tool, the Active Soil Depressurization (ASD) system, is highly effective at reducing radon concentrations. But in modern, energy-efficient (tight) homes, radon mitigation alone may not ensure healthy indoor air quality.
That’s exactly why we launched a free, self-paced CE course — ASHRAE 62.2 Ventilation Standards for Radon Mitigators — to help professionals understand this growing challenge (we’ll explain why this matters below).
And here’s the critical question many mitigators overlook: Does an ASD system count as proper ventilation? The short answer: No — not under ASHRAE 62.2.
Why ASD Is Not a Ventilation System
In today’s high-performance homes, radon mitigation and ventilation are two separate systems with two different purposes. While both influence air movement, they are designed to solve fundamentally different problems.
ASD systems perform source control by creating negative pressure beneath the slab to prevent radon and soil gases from entering the home. In contrast, ASHRAE 62.2 ventilation systems are designed for dilution, supplying controlled outdoor air to reduce indoor pollutants and maintain acceptable indoor air quality (IAQ).
An ASD system does exhaust some conditioned indoor air, but this airflow is not a designed ventilation strategy. The amount of air removed depends entirely on how tight the home is, where cracks and openings exist, and how the system interacts with natural pressure forces like wind and stack effect. As a result, the airflow is unmeasured, unpredictable, and unevenly distributed across the living space.
ASHRAE Standard 62.2 – Ventilation and Acceptable Indoor Air Quality in Residential Buildings, on the other hand, requires a dedicated mechanical ventilation system with known and verifiable performance. This means the airflow must be measurable (in CFM), operate continuously or on a programmed schedule, and deliver fresh air to occupied spaces in a controlled manner.
This may include:
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Exhaust-only systems
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Supply system
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Balanced systems using HRV or ERV
An ASD fan cannot be used to claim compliance with ASHRAE 62.2.
Why This Matters More Than Ever in Modern Homes
High-performance and zero-energy homes follow the principle: Build tight. Ventilate right.
The tighter a home becomes, the more critical it is that ventilation is intentional and engineered. When a mitigation system is installed without evaluating whole-house ventilation, it can unintentionally disrupt the home’s pressure balance.
In practice, this may lead to increased negative pressure indoors, which can interfere with combustion appliances, increase humidity, create comfort issues, and cause unnecessary energy loss. In some cases, mitigation systems can even make radon entry more aggressive by increasing suction across the slab.
In other words, you may solve the radon problem, but introduce new IAQ and performance problems in the process. We covered in detail in the radon ventilation CE course.
ASHRAE 62.2 Is Now a Professional Standard
ASHRAE 62.2 is no longer just an HVAC guideline. It has become embedded in residential building codes, green building programs, and federally funded housing initiatives.
It is commonly referenced in:
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LEED for Homes
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New construction and energy retrofit projects
For many jobs, understanding ASHRAE 62.2 standards is now part of professional compliance and liability protection.
Yet in reality, most mitigation contractors never calculate ventilation rates, never measure airflow, and never verify whether a home meets minimum ventilation standards after mitigation.
This gap doesn’t just limit technical performance; it limits professional credibility. It also creates real health, legal, and contractual risk, especially in regulated projects or new construction environments.
How Balanced Ventilation Improves Radon Mitigation
When properly designed, balanced ventilation systems (HRV/ERV) can actually enhance the performance of an ASD system.
From a building science perspective, balanced ventilation helps stabilize pressure dynamics inside the home. This reduces extreme negative pressure conditions that can increase soil gas entry and compromise mitigation effectiveness.
It also minimizes the loss of conditioned indoor air. A well-sealed home with controlled ventilation allows the ASD fan to draw primarily from beneath the slab, rather than pulling heated or cooled indoor air through foundation leaks.
Finally, continuous and controlled airflow improves system consistency. HRV and ERV systems smooth out fluctuations caused by wind, seasonal temperature differences, and the operation of appliances like dryers or bath fans.
The result is more predictable radon control and more stable indoor air quality.
When Ventilation Alone May Solve Slightly Elevated Radon
In homes with radon levels close to action thresholds - typically between 2–4 pCi/L or slightly above EPA’s action level of 4 pCi/L - a properly sized balanced ventilation system may be enough to address both radon and overall IAQ.
By continuously exchanging stale indoor air with fresh outdoor air, these systems dilute radon concentrations and prevent long-term accumulation. At the same time, HRVs and ERVs recover heat and moisture, making them far more energy-efficient than simple exhaust fans or natural ventilation strategies.
This approach is especially relevant in:
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New construction homes
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Passive or net-zero homes
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Energy retrofit projects
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Weatherization programs
In all cases, ventilation-only strategies must always be followed by post-install retesting to confirm that radon levels remain safely below action thresholds.
Advance Your Expertise in Radon & Ventilation
Modern radon mitigation is no longer just pipe and fan. It requires a working understanding of building science, pressure dynamics, indoor air quality systems, and ventilation standards.
That’s exactly why Ecosense created the ASHRAE 62.2 Ventilation Standards for Radon Mitigators CE course at Ecosense Learning Center. This course is designed specifically for radon professionals, not HVAC engineers.
You will learn how to:
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Calculate ventilation requirements
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Size and verify airflow (CFM)
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Identify when ventilation can support or replace ASD
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Document compliance for codes and programs
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Avoid liability in tight homes
This training is ideal for:
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NRPP / NRSB CE credits
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Mitigators working in new construction
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Energy retrofit and weatherization projects
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Professionals expanding into IAQ services
👉 Enroll now in ASHRAE 62.2 training for radon professionals at Ecosense Learning Center
FAQ
Q: Does an ASD system count as proper ventilation under ASHRAE 62.2?
A: No. An Active Soil Depressurization (ASD) system does not meet the requirements of ASHRAE 62.2 because it does not provide controlled, measurable outdoor air to occupied spaces. ASD performs source control for radon, but it is not a designed mechanical ventilation system.
Q: What is the difference between radon mitigation and whole-house ventilation?
A: Radon mitigation focuses on preventing radon from entering the home through source control, typically using an ASD system. Whole-house ventilation focuses on diluting indoor pollutants by supplying controlled outdoor air, as required by ASHRAE 62.2, to maintain acceptable indoor air quality.
Q: Why is ASHRAE 62.2 important for radon mitigators?
A: ASHRAE 62.2 is important because it defines the minimum ventilation requirements for residential buildings. In tight homes, mitigation systems can affect pressure balance and indoor air quality. Understanding ASHRAE 62.2 helps radon professionals ensure compliance, avoid liability, and protect occupant health.
Q: Can balanced ventilation systems improve radon mitigation performance?
A: Yes. Balanced ventilation systems using HRV or ERV technology can stabilize indoor pressure, reduce extreme negative pressure, minimize conditioned air loss, and support more consistent radon control when used alongside an ASD system.
Q: When can ventilation alone be used to reduce radon levels?
A: In homes with slightly elevated radon levels (typically between 2–4 pCi/L or just above 4 pCi/L), a properly sized balanced ventilation system may be sufficient to dilute radon and improve overall indoor air quality. Post-installation radon testing is always required to confirm effectiveness.