How to test your home properly, what the number means, and what it costs to fix — written for Alberta’s geology and Calgary’s winters.
Radon is a radioactive gas produced as uranium in soil and bedrock breaks down. It seeps up through foundations — through cracks, construction joints, sump pits, and the gaps around pipes and floor drains — and accumulates indoors. You cannot see it, smell it, or taste it. There is no symptom that tells you your home has it.
It is the second-leading cause of lung cancer in Canada after smoking, responsible for roughly 3,200 deaths a year. Unlike most of the hazards in a home, radon is not a maintenance problem or a construction defect — it comes from the ground the house sits on, which is why a brand-new home can test higher than a century home two streets over.
The good news is that radon is one of the few serious home hazards that is cheap to measure and reliably fixable. A test kit costs less than dinner out. Mitigation, if you need it, is a one-time cost in the low thousands and works permanently.
Alberta's geology, our climate, and why the only test worth trusting runs for three months.
Alberta sits on geology with meaningful uranium content, and the province consistently records radon levels well above the Canadian average. Prairie soils and the glacial till under much of Calgary allow gas to migrate readily toward the surface — and toward the negative pressure of a heated basement.
Radon concentration is a function of how much gas gets in versus how fast it leaves. For roughly half the year, Calgary homes are sealed shut and heated. Warm air rises and escapes through the upper floors, which draws replacement air in at the lowest point of the house — the basement — pulling soil gas along with it. This is called the stack effect, and it is why the same home will almost always test higher in January than in July.
This surprises people. Modern homes are built far more airtight than homes from the 1960s, which is excellent for heating bills and terrible for radon dilution. A well-sealed 2015 build in a new community can and does test higher than a draughty older home. Age of home tells you nothing about radon risk.
Radon varies enormously house to house, even between homes with identical floor plans on the same street. It depends on the specific soil beneath your foundation, the pathways into your particular basement, and how your home is ventilated. A low reading next door is not evidence about your home — it is a completely separate measurement.
Radon is not a steady number. It rises and falls with barometric pressure, wind, temperature, whether your furnace is running, whether a window was open, and whether it snowed. A reading taken over three days captures three days of weather — not how you actually live in the house.
Two- to seven-day tests can be off from the home's true annual average by a wide margin in either direction. That cuts both ways: a short test can frighten you into mitigating a home that does not need it, or reassure you about a home that does.
Health Canada recommends a long-term test of at least three months — 91 days minimum — using a passive alpha-track or electret detector. That duration averages out the daily and weekly swings and gives you a number that reflects your actual exposure.
Run your test between roughly October and April, when the house is closed up and the furnace is cycling. This is deliberately the worst-case window, and that is the point — you want to know your exposure when it is highest, not when every window has been open for a month. A summer test on a Calgary home routinely understates the winter reality.
Short-term tests are screening tools, not decisions. They have a legitimate role in a real estate transaction, where a 91-day test is impossible inside a condition period — covered in the next section. Treat the result as a flag, not a verdict, and follow up with a proper long-term test after possession.
The detector goes in the lowest level of the home where you spend at least four hours a day. For most Calgary families that is a developed basement — a family room, home office, gym, or bedroom. If your basement is genuinely unfinished storage nobody uses, test the main floor instead. Do not test the crawlspace or an unused mechanical room and then treat that number as your exposure; it will read high and it is not where you breathe.
Put the detector at breathing height — roughly one metre off the floor — and at least 50 cm away from exterior walls, 20 cm from any other object, and well clear of windows, doors, vents, fireplaces, and heat sources. Do not put it in a kitchen, bathroom, or laundry room, where humidity and exhaust fans distort the reading. A shelf or bookcase in the middle of a finished basement room is close to ideal.
Do not change how you use the house to make the number look good. Do not crack windows, run extra fans, or leave the basement door open. The test is measuring your ordinary life in the home — if you alter your habits for 91 days, you have measured a house nobody lives in.
Record the exact start and end dates, seal the detector as instructed, and mail it to the lab promptly — the analysis is time-sensitive. Results usually come back within two to three weeks as a single number in becquerels per cubic metre (Bq/m³).
This guide is about testing and fixing. This chapter is the reason the rest exists, stated plainly and without alarm.
A radioactive gas produced by the natural decay of uranium in soil and rock. It is colourless and odourless, it moves through the ground and into buildings through cracks, joints and openings, and it collects where air is still: basements and lower floors, especially in winter when homes are sealed.
Breathing radon over years exposes lung tissue to radiation. Health Canada identifies it as the leading cause of lung cancer in people who have never smoked, and the risk is higher again for smokers. The risk is about long exposure at elevated levels, not about a single reading.
Canada's guideline level is the point at which Health Canada recommends taking action to reduce radon. Levels below it are not zero risk; the guideline is a practical threshold for when mitigation is worth doing. Lower is better.
The geology under the city, long winters with sealed homes, and construction practices that put living space below grade combine to produce more elevated readings here than in most Canadian cities. That is the reason to test, not a reason to worry before you have.
A good test is not expensive, and a bad one is worse than none. Here is how to choose between a do-it-yourself kit and a certified measurement professional.
A passive detector you place and leave for the full measurement period, then mail to a laboratory. Choose one from a supplier whose laboratory is certified under the Canadian radon programme and whose kit includes the lab fee. The instructions on placement are the most important part of the package.
A measurement professional certified under the Canadian National Radon Proficiency Program places the detectors, documents the conditions, and reports with a certificate. For a real estate transaction, or when a result will be relied on by someone else, the certificate matters.
Electronic monitors give a running reading and are useful for watching a level over time, especially after mitigation. For the first decision, the long-term passive test remains the reference, because it averages over the whole period.
Short kits sold as quick answers, detectors placed in the wrong room, and tests run with windows open. Each produces a number that looks precise and means little.
What to do when you are buying, how to read your result, and what mitigation actually involves.
A proper radon test takes 91 days. A Calgary condition period typically runs seven to fourteen. You cannot do a valid long-term test before you have to decide whether to buy the home — and any agent who tells you otherwise is describing a screening test.
First, ask whether the seller has tested. More Calgary sellers have results than you would expect, particularly if they mitigated. If a mitigation system is installed, ask for the post-mitigation test result and the installer's paperwork — a system with no verification test behind it is an unknown.
Second, you can run a short-term screening test during conditions — typically a 48-hour to seven-day device placed by a certified professional, sometimes as an add-on to the home inspection. Understand what you are getting: a snapshot that flags a serious problem but cannot rule one out.
Third, and most practically for most buyers: proceed on the purchase and budget for the possibility. Mitigation is a known, bounded cost in the $1,500–$3,500 range. It is not a reason to walk away from the right home — it is a line item.
If a screening test comes back dramatically high — several times the guideline — that is worth raising during conditions, and worth a conversation about who pays for mitigation. A result modestly over 200 Bq/m³ on a two-day test is not proof of anything and is a weak negotiating position. We will tell you honestly which situation you are in.
Whatever happens during conditions, start a long-term test in your first heating season in the home. This is the number that actually matters, and it is the one almost nobody follows through on.
Health Canada's action guideline is 200 becquerels per cubic metre. Above that level, remediation is recommended, and the guidance is to act within two years — or within one year if you are above 600 Bq/m³.
This is the part people miss. 200 Bq/m³ is an action threshold, not a safety line. Risk is continuous: 190 is not safe and 210 is not dangerous — the risk simply rises with concentration and with years of exposure. The World Health Organization suggests a reference level of 100 Bq/m³, half the Canadian figure. If you test at 120 and have a young family sleeping in the basement, mitigating is a perfectly rational choice even though no rule requires it.
Radon and tobacco smoke are not additive — they compound. A smoker living in a high-radon home carries a substantially greater lung cancer risk than either exposure alone would suggest. If anyone in the household smokes or vapes indoors, treat a borderline result more seriously.
Re-test rather than agonize. A second long-term test in a different room on the same level, or in a subsequent heating season, costs another $50 and gives you a much firmer basis for a $3,000 decision.
The proven fix is Active Soil Depressurization (ASD). A pipe is cored through the basement slab into the gravel beneath it, routed up through the house or along an exterior wall, and fitted with a continuously running inline fan that vents above the roofline. The fan holds the area under the slab at slightly lower pressure than the basement, so soil gas is drawn out and exhausted before it can enter the home.
It is not a filter, and it is not a sealant. It redirects the gas — which is why it works so well and keeps working.
In Calgary, expect $1,500–$3,500 for a typical single-family installation, varying with foundation type, how the pipe has to be routed, and whether you want it concealed. A correctly designed system typically cuts radon by 80–99%, routinely taking a reading of 600 down under 100. Running cost is modest — the fan draws roughly as much power as a lightbulb, plus some conditioned air loss.
Hire a C-NRPP-certified radon mitigation professional. This is a specialty: fan sizing, pipe routing, slab sealing, and exhaust placement all determine whether the system performs. A general contractor coring a hole and mounting a bathroom fan is not mitigation, and badly placed exhaust can pull radon back into the house.
A mitigation system without a follow-up test is an assumption. Run another long-term test after installation to confirm the result, and keep the paperwork — a documented before-and-after is a genuine asset when you sell.
Alberta building code has required new homes to include a radon rough-in since 2015 — a capped pipe stubbed through the basement slab, sitting ready for a fan. Most owners of newer Calgary homes have no idea it is there. Look for a capped vertical pipe in the mechanical room or a corner of the basement, often labelled.
This matters, and builders' sales staff sometimes blur it. The rough-in is plumbing, not protection — with the cap on and no fan, it does nothing at all. It simply means that if you test high, activating the system is faster and cheaper than a retrofit, often in the $800–$1,800 range rather than the full cost.
Airtight new construction and the stack effect mean new Calgary homes frequently test above the guideline. Being new is not a defence, and the code rough-in is not a substitute for a measurement. Run your 91-day test in the first winter after you take possession.
If you are buying new construction, ask the builder where the rough-in terminates and whether they offer to activate it as an upgrade. Getting it done during construction is nearly always cheaper than after drywall and landscaping are in.
Even with a clear result, re-test roughly every five years. Soil conditions shift, foundations develop new cracks, and the ground around a house changes as landscaping and drainage age.
Re-test after a basement development, new windows, a furnace or HVAC replacement, foundation repair, a new sump pit, or significant weatherstripping and air sealing. Anything that changes how air moves through the house can change your radon level — and energy-efficiency upgrades usually push it upward by tightening the envelope.
Confirm the system worked with a long-term test, then re-test every few years to verify it is still performing. Fans do fail. Check the manometer — the small U-shaped pressure gauge on the pipe — a few times a year; if the fluid levels are even, the fan has stopped.
File your test results and any mitigation documentation with your home records. In Alberta, a known radon issue is the kind of thing a seller may need to address on the property disclosure statement, and a documented test with a working system is a far better answer than a shrug.
Chapter six explained how mitigation works. Choosing who does it decides whether it works, and whether a future buyer will trust it.
Use a contractor certified for mitigation under the Canadian National Radon Proficiency Program. Certification means training in system design, diagnostics and the standards a system must meet, and it is what a buyer's inspector or lawyer will ask about when you sell.
A good contractor tests the sub-slab communication before designing the system, to see how air moves under the slab and where the suction point should go. A contractor who quotes a system without looking under the slab is guessing.
It should specify the suction point location, the fan model and its location, the discharge point and height, the sealing work included, and the post-mitigation test. Fans belong outside the living space or in a ventilated attic or garage, never in a finished basement room.
Reputable contractors guarantee a result below the guideline and return to adjust the system if the first test does not achieve it. Get the guarantee in writing and keep it with the house documents.
Once a system is in, it runs quietly for years. It still needs a little attention, and knowing what normal looks like keeps it that way.
Most systems include a simple U-tube gauge on the pipe. When the fan is running and drawing suction, the liquid levels are uneven. If they level out, the fan has stopped. Look at it when you change the furnace filter.
Fans run continuously and last for years before they need replacing. A new noise, a rattle or a change in the gauge is the signal to call the contractor. Do not switch the fan off to save power; the system only works while it runs.
Test again a year or so after installation and then on the schedule in chapter eight, and after any renovation that changes the basement, the heating system or the home's air tightness. Keep every result.
A basement development, new flooring over the slab, or a change to the furnace can alter how the system performs. Tell the contractor before the work and test after it.
A seller with a test result and, where needed, a mitigation certificate is a seller with one fewer question at the inspection. Here is how to handle radon on the selling side.
A long-term test done well before listing gives you the result in time to act. A low result is a document for the listing file. A high result is a mitigation job done on your schedule rather than negotiated in a buyer's condition period.
If you know your home tested above the guideline and it has not been mitigated, that is information a buyer would want, and your REALTOR® will advise you on how it is disclosed. A mitigated home with a post-mitigation test is a positive disclosure, not a negative one.
Buyers increasingly test during the condition period, often with a short test that overstates or understates the true level. If a buyer's short test comes back high, offer your long-term result if you have one, or agree to mitigation with a certified contractor rather than losing the sale over a number that may not be real.
Mitigation is a defined cost with a predictable outcome. It is easier to agree a credit or a completed installation than to argue about the risk, and buyers accept a documented fix readily.
We raise radon on every home we help a client buy — before conditions come off, not after. If a screening test comes back high we will tell you honestly whether it is worth negotiating over, and if you are selling a mitigated home we treat that documentation as the asset it is.
Whether you are buying, selling, or you have just opened a test result you do not like, we can walk you through what it means for the transaction and what it realistically costs to put right.
Book a CallThis guide is for general information only and is not legal, financial, insurance, inspection, tax, or condo document review advice.
Buyers and homeowners should seek advice from appropriate professionals — including their lawyer, mortgage professional, home inspector, insurance provider, qualified condo document reviewer, accountant where applicable, and REALTOR® — before making decisions or removing conditions.
Calgary Listings Group has been helping Calgary buyers and sellers make informed decisions for more than 28 years.
