Keep Radon on your Radar

By: Gord Cooke

Families who are hunkered down in their homes have air quality on their minds. While the pandemic may be seen as a short-term challenge, we can all foresee that the way we live and work in our homes will be affected for years to come.

I was recently asked to review proposals a friend had received from a couple of HVAC contractors for a furnace, air conditioner and hot water heating system update. Both contractors added options for addressing air quality in my friend’s home. One of the proposals included an option to check radon levels in the basement. In speaking with my friend, he said he told the contractors his home office was in the basement.

A primary concern in upgrading his system was to ensure the office was comfortable and healthy. I was encouraged, that for at least one contractor, radon was on their radar as one of the most important indoor air quality (IAQ) parameters in Canadian basements.

Be mindful that in every house you visit this spring, you may actually be assessing and servicing simultaneously the air quality needs of a home, an office and a school. That air quality risk assessment must include radon, since according to Health Canada, “Long-term exposure to radon is the second leading cause of lung cancer after smoking and the leading cause of lung cancer for people who have never smoked.” Moreover, the longer the exposure, the greater the risk.

As our customers have changed the way they live, work and play in their homes, be sure to recalibrate your assessment of their needs in light of the best available industry information. Balanced ventilation is a key component in ensuring the healthiest possible air during the shorter-term pandemic, and it is one of the appropriate strategies for the much longer-term concern of radon mitigation. Recognize the importance of the radon issue and work with qualified radon professionals to ensure your customers are breathing the healthiest possible air.


Strategies for Mitigating Risk

The strategies for mitigating a building with high radon levels are also well defined and the test results will help determine which strategy is most appropriate for each building. The most effective strategy that is recommended by the World Health Organization (WHO), is sub-slab depressurization (SSD). This is where air is drawn from under and around the slab via a pipe and inline fan and exhausted outside. In more and more municipalities, a rough-in for sub-slab depressurization is now required in new buildings. The rough-in consists of a perforated pipe embedded in the stone drainage layer over which a sealed sheet of polyethylene or another approved radon barrier is applied before the concrete floor is poured. The collection pipe, which is usually four-inches in diameter for residential applications is stubbed up above the slab and capped off. If after the building is completed, long term testing shows radon levels are above the 200 Bq/ m3 then an exhaust fan approved for radon mitigation applications is installed on the rough-in pipe and vented to the outside.

To create a sub-slab depressurization system in an existing home it may be possible to utilize the existing sump-pump pit and associated drainage pipes. To test the effectiveness of this strategy, small 3/16-in. to ½ in. diameter test holes can be drilled through the slab in a few locations. An exhaust fan is then connected, either to a sealed cover of the sump pit or directly to the drainpipe. The hope is the fan will create a slight suction/negative pressure beneath the slab to capture the radon gas and eject it outside the home. The effect can be validated with a manometer to detect even a slight negative pressure in each of the test holes. While sub-slab depressurization is considered the most effective approach, professional contractors can imagine how obtrusive or disruptive an SSD approach could be in existing buildings.

Fresh air ventilation systems can also be effective in mitigating radon, specifically in newer, tighter homes, as the process of exhausting stale, radon-filled air and diluting the air in the building with fresh air lowers overall concentration levels. It is important to recognize that building codes in Canada changed in the early 1990s to include the requirement for a continuous or “principal” ventilation system. The most common strategy used was an “exhaust-only” system; an exhaust fan running more or less continuously. This strategy induces a slight negative pressure on the whole house and could draw soil gases into a basement. For radon mitigation, a balanced ventilation strategy such as heat or energy recovery ventilation (HRV or ERV) systems are recommended.


A Different Strategy

Furnaces and air conditioners in 20- to 30-year old houses are nearing the end of their service life. This is an opportunity for HVAC contractors to upgrade the ventilation strategy to a balanced system when upgrading the system. This method is actually more common than sub-slab depressurization in much of Europe. A control called a radostat detector measures the radon level in real time. The control closes a set of contacts when radon levels rise above 150 Bq/m3. This contact could be wired to the highspeed override circuit on HRVs and ERVs to pull the radon level back down to a safe level. Sub-slab depressurization is considered the most effective approach and will be recommended by qualified radon mitigation professionals in buildings where radon levels far exceed the 200 Bq/m3 action level.


Assessing Radon Risk

Radon is a gas formed by the breakdown of uranium, a natural radioactive material found in all soil and rock. Without measurement it is impossible to know or predict the level of radon in any specific home. However, it may surprise you that assessing radon risk is about as definitive as it gets in the IAQ world. There are well defined test protocols, measurement tools and action recommendations promoted by Health Canada. There are recognized training and certification programs for professionals wanting to measure or mitigate radon in Canadian buildings. Visit the Health Canada website ( where you will find links to a radon certification process offered by the Canadian-National Radon Proficiency Program (C-NRPP). C-NRPP offers certification for radon measurement and mitigation professionals. Mechanical contractors should have at least a referral relationship with radon professionals in your area (see

We measure radon concentration in becquerels per cubic meter (Bq/m3). In Canada the average home contains concentration levels of approximately 42 Bq/m3 of radon, and the average outdoor concentration is around 10 Bq/m3. The current actionable level (the point at which mitigation measures are recommended) set by Health Canada is 200 Bq/m3 or more, lowered from 800 Bq/m3 in 2007. For comparison, the US Environmental Protection Agency’s actionable level is 148 Bq/m3, and the World Health Organization’s is 100 Bq/m3 – half that of Health Canada. A 2014 study concluded that approximately 233 lung cancer deaths per year could be prevented in Ontario if all houses with concentrations above 100 Bq/m3 were remediated. According to Health Canada Guidelines, mitigation decisions should be based on measurements taken over the course of 91 to 365 days because of the potential for false-low/high depictions of radon concentration inherent in short-term tests. This is a key point as you consider investing in the radon opportunity; it involves a long-term customer relationship.