When to retest a home for radon

The baseline: every two years

For a house with an active mitigation system, retest every two years for as long as the system is in service. For a house without one that previously tested low, every two years is a reasonable interval as well, and there is no good argument for stretching it much beyond that.

The reason is that fans fail silently, houses settle and crack, and mechanical systems get replaced. Two years is short enough to catch drift before it becomes years of unnecessary exposure and long enough to be a habit rather than a chore.

The triggers that matter more than the calendar

Anything that changes the interface between the house and the soil, or the way the house moves air, warrants a test regardless of when the last one happened.

Foundation work of any kind — repair, underpinning, new drain tile, a new sump, an egress window cut into a foundation wall — disturbs the barrier and opens or closes pathways. Basement finishing alters the air balance and puts finished surfaces over joints that were previously accessible.

Mechanical changes matter more than people expect. A new furnace, a different HVAC configuration, or a change in duct layout alters the pressure relationship between the lowest level and the ground. Envelope work — replacement windows, air sealing, added insulation — reduces unintentional ventilation and can strengthen the stack effect.

And on a mitigated house: any fan replacement, any modification to the pipe run, and any period during which the system was switched off.

• Foundation repair, underpinning, or structural work
• New drain tile, a new sump pit, or a new egress window
• Basement finishing or conversion to living space
• Furnace, HVAC, or ductwork replacement
• Replacement windows, air sealing, or added insulation
• Radon fan replacement or pipe-run modification
• Any period with the mitigation system switched off
• Buying or selling the house

Why the manometer is not a retest

The gauge on a mitigation pipe reports one thing: whether the fan is developing suction. That is genuinely useful — a level manometer is an unambiguous warning — but it says nothing about the concentration in the room where your family sits.

A system can be pulling perfectly well and still leave part of the slab uncovered after a renovation, or lose ground because the house changed around it. Only a measurement in the living space answers the question the system exists to answer.

Check the manometer monthly as a habit. Retest on the schedule. They are complementary, not alternatives.

Retesting around a transaction

Buying: test during the inspection period regardless of what the seller provides, including on a house that already has a system. A current result under conditions you control is what you will be negotiating from.

Selling: a fresh short-term test before listing removes the surprise, and on a mitigated house it converts the system from an open question into a documented improvement. Where a state requires disclosure of known radon information, the practical effect of testing is that you disclose a current number rather than an old one.

After mitigation as part of a sale: the post-mitigation verification test is the deliverable and should be completed and delivered before closing, not promised afterward.

Short-term or long-term for a retest?

For a routine two-year check, either works, and a long-term alpha-track detector left in place for ninety days or more gives you a better picture of what you actually live with across seasons.

For verification after mitigation, after corrective work, or inside a transaction, use a short-term test under closed-building conditions — you need a prompt, controlled, comparable answer.

Whichever you use, put the device where the previous one was. Comparing a basement result to a first-floor result tells you almost nothing about whether the house changed.

Keep the record

File every result with its date, location, device type, and conditions, alongside the mitigation scope, credential number, verification test, and fan warranty. Over a few years that folder becomes the most persuasive document in a future sale.

It also makes the next decision easier. A single reading is a data point; a series of readings across seasons and renovations tells you how your house actually behaves.