Selling a House With High Radon in Ontario: A Seller's Playbook
You got your home ready to list. Fresh paint, staged rooms, clean gutters. Then a radon test comes back at 380 Bq/m³. That’s nearly double Canada’s action level of 200 Bq/m³.
Take a breath. A high radon reading is not a reason to pull the listing. It’s a fixable problem with a known cost.
This guide covers what you have to tell buyers in Ontario, whether to fix it first or price it in, and how to test fast enough to keep your sale on track.
The short version:
- Ontario has no law that forces you to test for radon or disclose it. But you can’t lie if a buyer asks, and hiding a known danger can come back on you.
- Fixing radon before you list is usually the cleaner play. A system costs $2,800 to $3,800 and takes about a day.
- A high reading is a price talk, not a deal killer. The fix costs less than a new roof or furnace.
- A fast resale test runs 48 to 72 hours and costs $399, so it fits a listing timeline.
- If you’re selling a newer build, the Tarion warranty may make the builder pay for the fix, not you.
- Always run your plan past your own real estate lawyer. This is a playbook, not legal advice.
Do you have to disclose radon when selling in Ontario?
There’s no law in Ontario that forces you to test for radon or report it. Radon isn’t on any required seller disclosure form.
But that’s not the whole story. Ontario resale runs on “buyer beware.” Still, a seller can get in trouble two ways.
- If a buyer or their agent asks you a direct question about radon, you can’t lie or dodge.
- If you know about a hidden danger and hide it on purpose, that can expose you later.
Radon is invisible and has no smell.
Many Ontario sellers fill out a Seller Property Information Statement, or SPIS. It’s optional. But if you choose to fill one out, every answer has to be true and not misleading.
This is exactly where a lawyer earns their fee. Ask your real estate lawyer how disclosure rules apply to your sale before you list. Rules shift, and your situation is specific.
Fix it before you list, or price it in?
You’ve got two real paths once a test comes back high. Fix it now, or sell as-is and let the buyer handle it.
For most sellers, fixing it first is the cleaner move. A clean re-test after the fix turns a scary word into a selling point.
Here’s how the two paths compare.
| Fix before listing | Sell as-is | |
|---|---|---|
| Upfront cost to you | $2,800 to $3,800 | $0 now |
| Listing message | ”Radon tested and fixed" | "Buyer to handle radon” |
| Buyer reaction | Reassured | Cautious, may lowball |
| Deal risk | Low | Higher, deals can stall |
| Negotiation | You keep control | Buyer holds the lever |
When you fix it first, you control the story. You hand buyers a low re-test number and a paid invoice. The problem is gone before it ever scares anyone off.
When you sell as-is, the buyer takes on the unknown. Wary buyers often ask for more than the fix actually costs. So a $3,500 problem can turn into a $6,000 price cut.
There’s a middle path too. Some sellers get a quote for the fix, then offer a credit at closing. That keeps the deal moving without paying the full cost upfront.
What high radon actually does to your sale
Let’s be honest here. There isn’t much hard Canadian data on the exact dollar hit radon puts on a sale price. Anyone who quotes you a precise percent is guessing.
But the logic is simple. Buyers price in risk they don’t understand. A fix has a known price, roughly $2,800 to $3,800.
A high reading you leave for the buyer tends to cost you more than the fix itself. Three reasons why.
- Buyers pad their ask to cover the unknown.
- A stalled deal costs you carrying time and bargaining power.
- The word “radon” spooks some buyers off entirely, shrinking your pool.
A radon problem is one of the cheapest home defects to fix. A new roof can run $12,000. A furnace can run $6,000. A radon system runs $2,800 to $3,800 and lasts for years.
A paid invoice and a clean re-test beat a scary word every time. You’re not selling a problem. You’re selling a home where a problem was already found and fixed.
So the price impact is real, but it’s mostly about fear, not the fix. Take the fear off the table and you protect your price.
The fast test that fits a resale
A normal long-term radon test runs 91 days or more.
For a listing, you need a number fast. That’s what a resale test is built for.
A short test with a calibrated monitor runs 48 to 72 hours under closed-house conditions. Windows shut, heating or cooling running as normal. Health Canada’s measurement guide allows this faster method for real estate deals.
At Breathe Radon Free, that real estate test is $399. We place the monitor, leave it at least 72 hours, then hand you a signed report.
A signed report matters when a sale is on the line. It’s hard for a buyer to wave away. And if you fix the radon, a second test gives you the clean number you show buyers.
Test in winter if you can. Closed windows and a running furnace pull more soil gas in, so winter readings run higher and safer to act on.
DIY test vs hiring a pro before you sell
For your own peace of mind, a $30 kit from the hardware store is a fine first check. Selling is different. The result has to hold up in a deal, and you’re on a clock.
Here’s how the two stack up when a sale is on the line.
| Factor | DIY mail-in kit | Professional test |
|---|---|---|
| Speed | 2 to 4 weeks for lab results | Report in days |
| Fits a listing timeline | Rarely | Yes |
| Trusted by a buyer | Weak, easy to dispute | Strong, signed report |
| Closed-house proof | None | Documented |
| Cost | $25 to $50 | $399 resale test |
| Best use | A first screen months ahead | Listing or closing a sale |
Go DIY if you’re months out and just want to know where you stand. A cheap long-term kit is perfect for that early look.
Hire a pro once you’re close to listing. A signed, defensible report is what a buyer’s agent and lawyer will actually trust.
One caution on the fix. Radon mitigation is not a weekend job for most homeowners. A poorly built system can make readings worse. Always check a mitigator’s credential on the C-NRPP directory before you hire.
Selling a newer build? The builder might pay
Here’s a path where the fix costs you nothing.
Did you buy your home new from a licensed builder on or after February 1, 2021? If so, Ontario’s Tarion warranty may cover radon mitigation.
The coverage is up to $50,000 per home, for a 7-year term. It switches on when a proper test reads at or above 200 Bq/m³.
For a seller, this is a real edge. You can fix the radon through the builder before you list, at no cost to you, then sell a home that tests clean.
To use it, your home has to be inside the 7-year window and a qualified test has to hit the trigger number. Our Tarion page walks through the full eligibility check.
What to do next
If you’re getting ready to sell in the Greater Toronto Area or surrounding Southern Ontario, test before you list, not after an offer lands. A surprise reading during a deal is the worst time to find out.
A clean result means one less thing for a buyer to question. A high result gives you time to fix it on your own schedule, before the pressure of a live deal.
You can read Health Canada’s plain-language radon overview for the health side. When you’re ready, request a quote for a fast resale test built for your listing.
Buying instead of selling? Our buyer’s playbook covers the other side of the deal.
Frequently asked questions
Do I legally have to disclose radon when I sell my home in Ontario?
There’s no Ontario law that forces radon testing or disclosure, and radon isn’t on a required form. But you can’t lie if a buyer asks, and knowingly hiding a danger can create liability. If you fill out a voluntary SPIS, your answers must be truthful. Ask your real estate lawyer how the rules apply to your sale.
Should I fix radon before listing or just tell buyers?
For most sellers, fixing it first is cleaner. A paid invoice and a clean re-test remove the fear that makes buyers lowball. Selling as-is is fine too, but wary buyers often ask for more than the fix costs. A middle path is to offer a closing credit for the work.
How much does it cost to fix high radon before a sale?
A radon mitigation system in Ontario runs $2,800 to $3,800 for a standard home and installs in about a day.
Will high radon lower my home’s value?
There’s little hard Canadian data on the exact dollar impact. The bigger risk is fear-driven lowballs and stalled deals, which usually cost more than the fix itself. Radon is the second leading cause of lung cancer in Canada, so buyers take it seriously.
How fast can I test my home for radon before I list it?
A resale test with a calibrated monitor runs 48 to 72 hours under closed-house conditions. With report writing, you get a signed result in about 5 days. That fits most listing timelines, unlike a mail-in kit that takes weeks.
Book a fast $399 resale radon test →
Authored by the Breathe Radon Free Team. Every claim is backed by a primary source linked above. Full bibliography at /sources.
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