What Happens After Mitigation

The install crew left this afternoon. The fan is running, the manometer is showing offset between the two columns, and your contractor handed you paperwork on the way out the door. Now what? When do you know it's working? When do you need to retest? What signs should you watch for over the next 5–10 years?

This page is the post-mitigation roadmap. Calmly answer those questions in the order they actually come up.

A working mitigation system is verified by a post-mitigation test. The EPA and AARST recommendations:^[1]

• Within 30 days of system activation.
• No sooner than 24 hours after the fan starts running, to let the system stabilize.
• 2 to 7 days of test duration.
• Closed-house conditions for 12 hours before and during the test. Normal in-and-out traffic is fine; sustained windows or doors open is not.
• Placed in the lowest livable level of the home, 2–6 feet above the floor, away from drafts, vents, and high-humidity areas.

Some Colorado contractors include the post-mit test in the install quote. Others charge $125–$200 separately. If your install quote was silent on the post-mit test, ask. A working system without a verified post-mit test is a working system you can't prove.

A common best practice: have an independent (non-installer) tester do the post-mitigation test to avoid any conflict of interest. EPA explicitly recommends this.^[1]

The post-mit test result should come back well below the EPA action level of 4.0 pCi/L. A properly designed system should bring most Colorado homes to under 2.0 pCi/L — often under 1.0.^[1] If your result comes back:

Quality contractors include a written guarantee that the system will achieve below 4.0 pCi/L on post-mit testing. If yours did and the test fails, they should add the additional suction point or upgrade the fan at no extra cost.

The manometer is your at-a-glance system health indicator. A monthly check takes 30 seconds:

1. Look at the two fluid columns. They should be at different levels — typically 0.5 to 2.0 inches of water column offset.
2. The offset doesn't have to be the same every time, but it should be reasonably steady — within roughly the same range month to month.

What to do if you see something different:

• Both columns at the same level → the fan isn't running. Could be a power issue (check the circuit), a fan failure, or a tripped GFCI. Call the original installer.
• Reading much lower than usual → the system is losing efficiency. Possible causes: fan starting to fail, a leak in the pipe, or a seal that has broken. Service call.
• Reading much higher than usual → less common but possible if the soil-gas conditions changed (e.g., a heavy rain saturated the soil). Worth noting but usually not urgent.

The EPA recommends retesting your home every 2 years, even with a working mitigation system.^[1] The reasons:

• Soil-gas conditions change over time as the home settles, foundations age, and water table conditions shift.
• Fans degrade slowly over their lifespan — a fan that's bringing levels to 1.5 pCi/L now might be at 3.5 pCi/L in five years.
• Climate and seasonal patterns affect radon levels. A test in summer captures different conditions than one in winter.

Colorado has significant seasonal swings — winter levels (sealed-up homes, stronger stack effect) are typically higher than summer levels. EPA notes that long-term tests average across seasons, which is why long-term tests are useful for re-verification.

You should also retest:

• After major remodeling that changes the foundation, basement, or HVAC.
• After adding new living space (finishing a basement, adding a room).
• If you notice the manometer behaving differently.
• Before listing the home for sale.

The fan is the only routine maintenance item. Most manufacturers warrant fans for 5 years; in practice they often run 7–10 years before needing replacement.^[1]

Signs your fan needs replacement:

• Audible humming, rattling, or grinding from the fan housing.
• Manometer reading dropping over time.
• Visible vibration or movement of the fan.
• A retest showing radon levels rising.

Replacement cost: $150–$400 in parts plus 1–2 hours of labor. Most Colorado contractors will replace the fan as a service call rather than a full new install.

Keep these documents permanently in a folder with your home records. They become part of your required SB23-206 disclosure if you ever sell the home:^[2]

• Original test report (the high reading that triggered the install)
• Contractor's written quote and final invoice
• System certification, DORA license documentation, NRPP or NRSB certification number
• Fan model number and warranty
• Post-mitigation test result certificate
• Any retest results going forward
• Any service calls or fan replacements

A buyer of your home is legally entitled to see all of this. A well-documented mitigation history is actually a selling point — it shows the radon problem is known, addressed, and verified.