After Radon Mitigation: What to Expect, When to Test, and Long-Term Maintenance

The First 48 Hours

Your fan is running. Here's what's happening:

The moment the fan turns on, it begins creating negative pressure beneath your slab. Sub-slab radon levels start dropping within minutes. Indoor air radon levels drop more gradually — the existing radon in your home takes time to clear through normal air exchange.

What you might notice:

• A low hum: The fan is running. Normal. Most people stop noticing it within a few days.
• Slight whistling: Sometimes occurs at pipe connections. Usually self-resolves or can be addressed with a small adjustment.
• The manometer is unequal: This is correct — it means the fan is creating negative pressure. Equal levels = fan problem.
• Radon levels still seem high on a monitor: Give it 24–72 hours. Digital monitors like the Airthings Corentium show rolling averages; the reading won't immediately reflect the new system.

The Post-Mitigation Testing Schedule

24-hour test (optional but recommended)

Run a short-term charcoal test immediately after installation. This gives you an early read and catches obvious system problems quickly. Labs offer 24-hour processing for post-mitigation tests — ask your contractor for a kit or buy one from the shop.

What a good 24-hour result looks like: 50–75% reduction from pre-mitigation level. A home that tested at 12 pCi/L should come back at 3–6 pCi/L at 24 hours; it will continue to improve over the next several weeks.

30-day test (the definitive test)

This is the number that matters. Run a short-term test between 24 and 90 days post-installation for your official confirmation result. The 30-day reading captures the system's stable ongoing performance under normal living conditions.

Target: Below 4.0 pCi/L. A well-installed system should achieve below 2.0 pCi/L in most homes. If your 30-day result is still above 4.0 pCi/L, contact your contractor — most provide a performance guarantee and will adjust the system at no charge.

Annual quick check

Check the manometer monthly. It takes 3 seconds. If the liquid levels equalize, the fan has failed — radon is no longer being actively vented.

Every 2 years: long-term test

Run a 90-day alpha track test every 2 years. This is the most accurate measurement method and catches gradual fan performance degradation before levels creep back up. Alpha track kits cost $25–$35.

When to retest sooner:

• After any renovation that opens the foundation (adding a sump, cutting new penetrations, remodeling the basement)
• After HVAC system replacement or modification
• After the fan is replaced
• If you notice the manometer reading has changed significantly

What Normal Looks Like Long-Term

A properly installed system requires minimal attention. The checklist:

Monthly (30 seconds):

• Glance at the manometer. Unequal levels = system working. Equal levels = call your contractor.

Seasonally:

• Note whether the fan hum sounds the same. A change in pitch or volume can indicate bearing wear.

Every 2 years:

• Long-term radon test ($25–$35). Mail the test kit, wait 90 days, confirm levels are still low.

Every 5–15 years:

• Fan replacement when the motor wears out. Cost: $150–$350 for parts and labor. This is the only maintenance expense the system has.

When Levels Rise After Mitigation

If a follow-up test shows levels creeping back up after previously being low, the most common causes:

1. Fan failure — check the manometer first. A failed fan is the most common reason for level increases.
2. New cracks or penetrations — renovations, settling, or plumbing work can open new entry points.
3. HVAC changes — a new or more powerful exhaust system can change house pressure dynamics.
4. System depressurization scope — rarely, radon enters through a path the original system doesn't cover. A contractor can assess with a diagnostic test.

Fan failure is the cause in the majority of cases. If the manometer is reading correctly (unequal), the system is running — and a contractor will need to diagnose what changed.

Fan Replacement: What to Know

Fans last 5–15 years. When yours needs replacement:

• Same footprint: The replacement fan usually mounts to the same pipe with minor modification.
• Upgrade option: If you've had marginal results, replacing with a higher-suction model (GX3 or GX5 instead of XP201) at replacement time can improve performance without rerouting pipe.
• DIY or pro: Fan replacement is within reach for mechanically comfortable homeowners. It's a simpler install than the original — no core drilling, just fan swap and electrical reconnection. Our DIY installation guide covers the process.

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