November 13, 2025

Does Your HRV Reduce Radon? What Ottawa Homeowners Need to Know

Does your HRV reduce radon in your Ottawa home? Learn what heat recovery ventilators can and can’t do for radon, why they’re not a standalone solution, and when ASD is the right answer.

If your Ottawa home has a heat recovery ventilator (HRV), you may have assumed it helps protect your family from radon. It’s a reasonable assumption — HRVs bring fresh air in and stale air out, and Ontario’s Building Code requires them in new homes. But when it comes to radon, there is an important gap between what HRVs are designed to do and what they actually deliver. This article explains how HRVs interact with radon, what the evidence shows about their effectiveness, when they can help, and when a different solution is needed.

What Is an HRV — and What Is It Designed For?

A heat recovery ventilator is a balanced mechanical ventilation system. It works by exhausting stale indoor air and simultaneously drawing in fresh outdoor air, exchanging heat between the two airstreams so that the incoming air is pre-warmed by the outgoing air. This process improves indoor air quality and reduces humidity without the energy penalty of simply opening a window in Ottawa’s cold winters.

HRVs (and their cousins, energy recovery ventilators or ERVs) are designed to address overall indoor air quality — removing moisture, odours, VOCs, and pollutants from a sealed home. Radon is one of many things they may help dilute. But dilution and removal are fundamentally different, and that distinction matters.

Why New Ottawa Homes Have HRVs — and What That Doesn’t Mean

The Ontario Building Code requires HRVs in new residential construction. This requirement exists primarily because modern homes are built to be significantly more airtight than older construction — better insulation and tighter building envelopes improve energy efficiency but reduce natural air exchange, which can allow pollutants (including radon) to accumulate.

Ottawa Public Health acknowledges HRVs as one tool that “remove excess moisture and indoor pollutants (radon, mould, household chemicals, and bacteria) and let fresh air inside.” This is accurate — but it describes what HRVs can contribute to, not what they reliably solve.

Having an HRV in your home is not a guarantee that your radon levels are acceptable. It is a starting point, not an endpoint.

What HRVs Actually Do for Radon: Dilution, Not Removal

The key distinction is this: an ASD system (radon fan) intercepts radon beneath your foundation before it enters the building. An HRV dilutes radon that has already entered the indoor air by mixing it with outdoor air.

This is why the effectiveness of HRVs for radon reduction is limited — and conditional.

The Canadian General Standards Board’s national radon mitigation standard (CAN/CGSB-149.12-2024) states that balanced ventilation systems (HRV/ERV) in airtight buildings have been shown to reduce indoor radon concentrations by an average of 20 to 50%. That range is meaningful, but notice the conditions:

  • “Airtight buildings” — the less airtight your home, the lower the actual reduction
  • “Average” — individual results vary widely depending on foundation type, radon entry rate, and system configuration
  • Running continuously — the HRV must operate around the clock; intermittent operation reduces effectiveness
  • Properly balanced — if the HRV is out of balance, it can create negative pressure inside the home, which actually draws more radon in through foundation cracksCompare that to Active Soil Depressurization (ASD): the same CGSB standard states ASD systems can provide a reduction of approximately 90% or more when properly designed and installed.

Why an HRV Alone Is Not a Radon Mitigation Solution

Several factors specific to Ottawa homes and climate make HRV-only approaches particularly unreliable for managing radon:

1. Ottawa winters limit effectiveness

HRVs have a defrost cycle — when outdoor temperatures drop sharply, some models temporarily stop exchanging air to prevent frost from forming inside the unit. During defrost mode, no fresh air comes in and no stale air goes out. In Ottawa’s climate, where winter temperatures regularly fall below -15°C, defrost cycles mean periods of zero radon dilution during exactly the times of year when homes are most sealed and radon accumulates fastest. The CGSB standard specifically notes this concern: a defrost cycle that depressurizes the building is not suitable for radon reduction.

2. Maintenance matters — and is often neglected

The C-NRPP Technical Bulletin on HRVs and radon notes that HRVs must be cleaned and balanced annually to function properly. When filters are clogged or the unit falls out of balance, it not only loses its radon-diluting effect but can actively worsen conditions by creating negative pressure that increases radon infiltration. Regular maintenance is an important part of regular HRV upkeep that is often neglected.

3. Continuous monitoring is required

Because an HRV’s effectiveness can change — through balance drift, filter buildup, mechanical wear, or seasonal variation — the CGSB standard requires that homes using ventilation as a radon mitigation strategy include continuous radon monitoring. Without a digital monitor running at all times, you have no way of knowing whether your HRV is actually keeping radon below the Health Canada guideline.

4. High radon levels may exceed what ventilation can address

For homes with elevated radon concentrations — particularly those above 600 Bq/m³ — the ventilation rates required to dilute radon to acceptable levels through an HRV alone can become impractical. The CGSB standard acknowledges this: “attempting to reduce high radon levels by using an HRV may result in impractical mechanical ventilation rates which would make such a system relatively expensive to operate.”

When an HRV Can Be Part of the Answer

HRVs are not useless for radon. In specific circumstances, they can play a legitimate role:

As a supplement to ASD: After an ASD system is installed and radon levels are reduced, an HRV contributes to overall indoor air quality and provides an additional layer of dilution. Many well-mitigated homes have both.

Where ASD is not practical: In buildings where soil depressurization is not feasible — certain slab configurations, some crawl spaces — the CGSB standard identifies ventilation as an alternative approach, subject to the conditions and monitoring requirements above.

Cleaning and balancing an existing HRV: If your home already has an HRV and you have not had it professionally cleaned and balanced recently, the C-NRPP bulletin notes that doing so can in some cases lower radon levels. It is a worthwhile first step — but one that should be followed by a radon test to confirm whether the results are acceptable.

The CGSB standard is clear about the hierarchy: “when practicable, the ASD technique is the preferred choice for radon mitigation.”

The Right Solution: Active Soil Depressurization

If your home tests above Health Canada’s 200 Bq/m³ guideline, the recommended solution is Active Soil Depressurization (ASD) — a fan-driven system that draws radon-laden soil gas from beneath your foundation and exhausts it outdoors before it enters the building. ASD addresses the source, not the symptom.

For more detail on how ASD works, what to expect during installation, and post-mitigation testing requirements, see Radon Mitigation in Ottawa.

Your HRV will continue to do its job — improving air quality and managing humidity. But radon mitigation requires a dedicated solution.

FAQ

Q: My new Ottawa home has an HRV — does that mean I don’t have a radon problem? A: Not necessarily. Ontario Building Code requires HRVs in new homes for air quality and energy efficiency reasons, but an HRV does not eliminate radon risk. The only way to know your home’s radon level is to test. Even a properly functioning HRV may not reduce radon to below Health Canada’s 200 Bq/m³ guideline.

Q: How much does an HRV reduce radon? A: According to the CGSB national radon mitigation standard (CAN/CGSB-149.12-2024), balanced ventilation systems in airtight buildings reduce indoor radon by an average of 20 to 50%. The actual reduction in any individual home depends on the building’s airtightness, the HRV’s balance and condition, and how continuously it operates. Compare this to ASD, which achieves 90% or more reduction.

Q: My HRV is running — does that mean my radon is being managed? A: Not necessarily. HRV effectiveness for radon depends on the unit being properly balanced, filters being clean, it running continuously, and your home being airtight enough for dilution to be meaningful. In Ottawa winters, defrost cycles can interrupt air exchange for periods of time. Without a continuous radon monitor, there’s no way to confirm your HRV is keeping levels below the guideline.

Q: Can a dirty or poorly balanced HRV make radon worse? A: Yes. An HRV that is out of balance — exhausting more air than it brings in — can create negative pressure inside the home. This negative pressure draws more soil gas (including radon) in through foundation cracks and gaps. The C-NRPP bulletin notes this as a specific concern and recommends having your HRV cleaned and balanced by a qualified professional.

Q: Should I have my HRV cleaned before testing for radon? A: If your HRV hasn’t been serviced recently, having it cleaned and balanced is worthwhile maintenance regardless of radon. The C-NRPP notes that in some cases, adjusting the HRV has been found to lower radon levels. After servicing, run a radon test to see where your levels stand.

Q: Can my HRV work alongside an ASD system? A: Yes, and this is common. An ASD system handles radon at the source — beneath your foundation. Your HRV continues to provide fresh air exchange and humidity control throughout your home. The two systems serve different purposes and work well together.

Q: If my radon levels are only slightly above 200 Bq/m³, is improving my HRV enough? A: It’s possible that a well-maintained, properly balanced HRV could contribute to bringing borderline readings down — but this is not a reliable strategy, and the CGSB standard requires continuous monitoring if ventilation is your mitigation method. For reliable, verified radon reduction to below the guideline, ASD is the recommended approach.

Q: Does running my HRV on high help more with radon? A: Increasing the ventilation rate does increase dilution, but this comes at an energy cost (more heating of cold Ottawa winter air) and may create balance issues if the system isn’t reconfigured properly. Higher ventilation rates can also cause moisture problems. The CGSB standard notes that impractical ventilation rates may make this approach prohibitively expensive for high radon levels.

Your HRV Is Not Your Radon Solution

Ottawa homeowners with HRVs — especially those in newer homes — often have a false sense of security about radon. The HRV is doing its job. But its job is not to mitigate radon. If you haven’t tested your home, you don’t know what your actual radon level is, regardless of what ventilation equipment you have.

Ottawa Radon Expert provides professional radon testing and Active Soil Depressurization installation for Ottawa homeowners. Our experienced local team assesses your home’s specific conditions, designs a system matched to your foundation type, and provides a post-mitigation warranty on every installation.

Contact Ottawa Radon Expert today to find out what your home’s radon level actually is — and what it will take to bring it to where it should be.

Internal links: Learn more about radon mitigation in Ottawa or how to test for radon.

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