What Is Radon? A Complete Guide for Ontario Homeowners

Chances are, you’ve heard the word “radon” somewhere. Maybe in a home inspection report. Maybe in a news article about lung cancer. Maybe from a friend who bought a home and was told to test for it.

Here’s what most Ontario homeowners don’t know: radon is the number one cause of lung cancer for non-smokers in Canada.

It kills roughly 3,200 Canadians every year. Most of them had no idea it was in their home.

This guide will tell you what radon is, why it matters for your family, how it gets into your house, and what to do about it. No fluff. No sales pitch. Just the facts in plain English from three C-NRPP certified radon professionals.

If you’ve only got two minutes, here’s the short version:

• Radon is a natural radioactive gas
• It seeps up from the soil beneath your home
• You can’t see it, smell it, or taste it
• 1 in 6 Ontario homes has elevated levels
• The only way to know is to test
• If levels are high, it’s fixable for a few thousand dollars

Ready for the longer version? Let’s go.

What is radon, scientifically?

Radon (chemical symbol: Rn) is a radioactive gas. It forms naturally in the ground as uranium in soil and rock breaks down over millions of years.

Uranium is everywhere. Not in concentrated dangerous amounts, but in trace levels across most Canadian soil, especially in the Canadian Shield and granite-rich regions. As uranium decays, one of its byproducts is radium. Radium decays into radon. And because radon is a gas, it doesn’t stay put in the soil. It rises.

Radon has no color. No smell. No taste. You could live in a home with dangerously elevated levels for decades and never know.

Here’s the part that matters for your health. When radon decays further, it releases tiny radioactive particles called alpha particles. You breathe those particles in. They stick to your lung tissue. Over time, year after year, they can damage the DNA in your lung cells. That damage can lead to lung cancer.

It’s not acute like carbon monoxide poisoning. You won’t collapse from radon exposure. It’s the slow, compounding kind of damage that builds over 10, 20, 30 years of continuous exposure.

Why Ontario homeowners should care

Let’s get specific. Here’s what Health Canada has documented:

• Radon causes 16% of all lung cancer deaths in Canada.
• In Ontario specifically, 13.6% of lung cancer deaths are attributable to radon. That’s roughly 847 Ontario deaths every year.
• Radon is the leading cause of lung cancer for people who’ve never smoked.
• Children are more sensitive than adults because their cells divide faster.

For context, you’re roughly 16 times more likely to die from radon than in a house fire in Canada. But nearly every home has a smoke alarm, and almost no home has a radon monitor.

Your risk scales with three factors:

1. How much radon is in your home. Higher concentration, higher risk.
2. How long you’re exposed. Longer exposure, higher risk.
3. Whether you smoke. Radon and smoking multiply each other’s risk significantly.

Even at moderate levels below the Health Canada guideline, decades of exposure add up. That’s why Health Canada recommends every home in Canada be tested.

How radon gets into your home

Here’s the mechanical reality. Your home is slightly negatively pressurized compared to the ground underneath it. This happens because:

• Warm air rises inside the home (the “stack effect”)
• Exhaust fans, clothes dryers, and HVAC systems pull air out
• Wind creates pressure differentials around the house

That negative pressure means your home is actively sucking air upward from the soil underneath. If there’s radon in that soil (and in most of Ontario, there is), your home pulls it inward through any opening it can find.

Common entry points:

• Cracks in concrete basement slabs
• Gaps around utility penetrations (water, gas, sewer lines)
• Sump pits, especially uncovered ones
• Crawl spaces with dirt floors
• Cold joints where the slab meets the foundation wall
• Floor drains

Once radon is inside, it collects in enclosed lower levels, especially basements. If your basement is finished and you spend time there (home office, playroom, gym, bedroom), your exposure is higher than someone who never goes down there.

Older homes with cracked foundations tend to have more entry points. But newer homes are often more airtight, which traps radon more effectively once it’s inside. There’s no home type that’s immune.

Who’s at risk in Ontario?

Short answer: every Ontario home could have elevated radon, but some areas are higher-risk than others.

Here’s what the data shows:

• Greater Toronto Area average: approximately 43 Bq/m³. Below the 200 Bq/m³ action guideline.
• Kingston: approximately 130 Bq/m³, with 25-50% of homes above guideline.
• Thunder Bay: similar to Kingston, with significantly elevated average levels.
• Ottawa: around 86 Bq/m³, with 16.7% of homes above guideline.

So the GTA looks relatively safe on average. But averages hide the tail. Individual homes in Oakville, Whitby, Toronto, or anywhere else can test far above 200 Bq/m³, even when the neighbor next door tests below it. Soil geology varies house-to-house. Foundation construction varies. HVAC systems vary.

The only question that matters is: is YOUR home high?

You find out by testing.

How to test for radon

There are two real options for Ontario homeowners.

Option 1: DIY test kit

• Cost: $30 to $60
• Where to buy: Canadian Tire, Home Depot, or through Take Action on Radon
• How it works: an alpha track detector sits in your basement for 91+ days, then gets mailed to a lab
• Pros: cheap, decent accuracy with a long-term test
• Cons: slow turnaround (4-8 weeks after mailing), no expert placement, basic report

Option 2: Professional test

• Cost: $249 to $399
• How it works: a C-NRPP certified technician drops off a calibrated continuous radon monitor, it runs for 3 to 7 days, they pick it up and deliver a full report
• Pros: fast, more accurate, expert placement, detailed report with recommendations
• Cons: more expensive

Our honest recommendation:

If budget is tight, do a DIY long-term kit. It’s dramatically better than not testing at all.

If you want a faster, more accurate answer, go professional. Especially if you’re buying or selling a home, or if the result will drive a meaningful decision like “do I let my kids sleep in the basement?”

Either way, don’t skip testing. It’s the only way to know.

What happens if your radon is high?

Three scenarios, based on your reading in Becquerels per cubic metre (Bq/m³):

Below 100 Bq/m³ You’re in good shape. Re-test every 5 years, or sooner if you renovate or change your HVAC system.

100 to 200 Bq/m³ Below the action guideline, but not zero risk. Health Canada recommends considering a long-term test to confirm. Some Ontario families choose to mitigate even at this level, especially with young children or heavy basement use. Your call.

Above 200 Bq/m³ Health Canada recommends mitigating within two years, or within one year if levels are significantly elevated. This isn’t optional in the same way a leaky roof isn’t optional. It’s a fixable health risk.

How radon mitigation works

A radon mitigation system is more mundane than it sounds. It’s:

• A plastic pipe that runs from under your basement slab up through the roof
• A quiet electric fan mounted in the attic or outside
• Some sealant to close obvious entry points

The fan creates suction under the slab. Instead of radon being pulled up into your home, it’s pulled out through the pipe and vented harmlessly above the roofline.

This method is called sub-slab depressurization. It’s what Health Canada recommends and what the EPA recommends. When installed properly, it reduces indoor radon by 80 to 99 percent in almost every home.

Typical cost in Ontario: $2,500 to $4,500, depending on home complexity. Installation takes one day in most homes.

The system runs continuously using roughly $5 to $10 per month in electricity. The fan typically lasts 20+ years.

That’s it. No magic, no ongoing chemistry. Just a pipe and a fan.

What to do next

Three actions, in priority order:

1. If you haven’t tested, test. Pick a method. Pick a date. Do it. Whether you buy a $40 DIY kit or book a professional test, the only wrong answer is not testing.

2. If you have tested, re-test on schedule. If your last test was more than 5 years ago, it’s stale. Radon levels change with seasons, renovations, and soil conditions.

3. If your test came back high, mitigate. It’s fixable. It’s not outrageously expensive relative to the risk. Every month you wait is another month of exposure.

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If you’re in the Greater Toronto Area and want us to handle testing or mitigation, we’ve published our prices at /services. You can get a quote in 60 seconds, book a call if you’d rather talk to someone, or just read more and come back later. No pressure, no sales follow-up unless you ask.

Your lungs are playing the long game. Make sure you are too.

References

1. Health Canada. “Radon: What You Need to Know.”
2. Canadian Cancer Society. “Radon.”
3. CAREX Canada. “Radon Profile.”
4. Lung cancer risk from radon in Ontario, Canada (peer-reviewed). PMC
5. Statistics Canada. “Fire-related deaths.”
6. Take Action on Radon. takeactiononradon.ca
7. EPA. “Consumer’s Guide to Radon Reduction.”

Authored by the Breathe Radon Free team. All authors hold active C-NRPP certification.