How a radon mitigation system works, what it costs in Ottawa, and the retest after
Updated
How sub-slab depressurization pulls radon out from under the floor, what goes into the price in Ottawa in 2026, and how and when to retest.
How sub-slab depressurization works
The most common fix is sub-slab depressurization, also called active soil depressurization. Health Canada describes it simply. A pipe goes through the basement floor and runs to an outside wall or up to the roof line. A small fan on that pipe draws soil gas from under the house and blows it outside before it can get in.
The fan creates slightly lower pressure under the slab than in the basement. Air then flows from the house into the soil, not the other way around. The fan runs all the time.
Health Canada's Take Action on Radon program says most systems are installed in less than a day and reduce radon by more than 80% in most homes.
What else goes into a good install
Sealing helps the fan do its job. Common add-ons are a sealed, gasketed sump lid, sealing major floor cracks and the gap where the floor meets the wall, and a membrane over any bare-earth crawlspace.
Pipe routing takes the most planning. In a finished basement, installers look for a closet, a utility room or the garage so the pipe is out of sight. Some newer homes in Stittsville and elsewhere have a capped radon rough-in pipe left by the builder, which can make the job simpler.
The work should follow the Canadian standard for existing homes, CAN/CGSB-149.12, Radon mitigation options for existing low-rise residential buildings. Health Canada recommends a mitigator certified by the Canadian National Radon Proficiency Program (C-NRPP). Ask to see the certification.
Ask for a simple pressure gauge on the pipe, such as a U-tube manometer, so you can see at a glance that the fan is pulling. Ask the installer to show you how to read it.
What it costs in Ottawa in 2026
These are indicative 2026 ranges for the Ottawa area, before HST. A site visit sets the price.
Sub-slab depressurization system: about $2,800 to $3,800.
Sealed sump lid or crawlspace membrane as an add-on: about $200 to $1,500.
Post-mitigation short test: often included, otherwise about $100 to $200.
The price moves with the pipe route, how many suction points the slab needs, the floor finish, and whether the pipe goes outside at the wall or up through the house.
Two houses that look alike can price differently. A slab poured over tight clay may need more suction than one over gravel. The fan uses a small amount of electricity year round. Ask for the fan model and its wattage so you know what you are signing up for.
The retest after
A system is only proven by a test. Health Canada's measurement guide says to retest during the next heating season after the system goes in, using a long-term test of at least 91 days, with the detector in the same spot as before where possible.
A short test right after installation can confirm the fan is making a difference. It does not replace the long-term retest.
The same guide says homes with an active system should be retested every 5 years to confirm it is still working. Retest sooner after a major renovation, a new addition or a fan replacement.
Living with the system
Check the gauge every month or two. If the fluid levels are even, the fan has stopped. Call the installer.
Keep the sump lid sealed and put back any caulking you disturb during other work. Do not block the exhaust outside with snow or storage.
Keep your paperwork together: the before test, the install details and the retest. Buyers and home inspectors will ask for it.
If a retest comes back above 200 Bq/m³, ask the installer to come back. Adding a suction point or better sealing is often part of the answer. A C-NRPP professional should stand behind the work.
Questions to ask before you hire
Are you C-NRPP certified for mitigation, and can I see the certificate number? Will the install follow CAN/CGSB-149.12?
Where will the pipe run, where will it exit, and what will I see inside and outside the house? Will you seal the sump and major cracks as part of the price?
Which fan will you use, and what is its warranty? What is your own warranty on the system, and does it cover a retest that comes back high?
Is a short test after installation included? Who supplies the long-term retest kit for the next heating season?
Get the answers in writing on the quote. Compare quotes on what is included, not only on the total.