Should I retest for radon?
Retesting is driven less by the calendar than by change. A house that has had a new furnace, a finished basement, new drain tile, or a round of air sealing is not the house that produced the last result.
This checks both: how long it has been, and which of the standard triggers apply to you.
Work it through
Everything below runs in your browser. Nothing you enter is sent to us or to anyone else — this page has no server to send it to.
Approximate is fine.
An active system with a fan and a manometer.
A different unit performs differently against the same conditions.
Changes the air balance and covers the joints that were sealed.
Changes the pressure relationship between the lowest level and the soil.
Reduces unintentional ventilation and can strengthen the stack effect.
Disturbs the barrier between house and soil.
A transaction needs a current, defensible measurement.
What this indicates
Reading your inputs…
Why this says what it says
The full working, shown rather than summarised. Nothing below is hidden behind a toggle, because reasoning that takes a click to reach has not really been shown.
What you told us, and what each answer did
| Your answer | Value | What it influences |
|---|---|---|
| Years since last test | 3 years | Approximate is fine. |
| A mitigation system is installed | No | An active system with a fan and a manometer. |
| Fan replaced since the last test | No | A different unit performs differently against the same conditions. |
| Basement finished or converted since | No | Changes the air balance and covers the joints that were sealed. |
| HVAC replaced or ducts altered since | No | Changes the pressure relationship between the lowest level and the soil. |
| Windows, insulation, or air sealing since | No | Reduces unintentional ventilation and can strengthen the stack effect. |
| Foundation, drain tile, sump, or egress work since | No | Disturbs the barrier between house and soil. |
| Buying or selling this house now | No | A transaction needs a current, defensible measurement. |
What we took on trust
- The figures you enter (years since last test) are taken exactly as typed. We have no way to check them against a device or a laboratory record.
- The yes/no conditions (a mitigation system is installed, fan replaced since the last test, basement finished or converted since, hvac replaced or ducts altered since, windows, insulation, or air sealing since, foundation, drain tile, sump, or egress work since, buying or selling this house now) are accepted exactly as you set them. Nobody has confirmed any of them, and the output assumes each is as stated.
What is still unknown
- Whether your house has changed in a way you have not told the tool about, including work done by a previous owner.
- How much any single trigger will move your specific number. The direction is predictable; the magnitude is house-specific.
Why this stops short of a decision
This runs entirely on what you typed. Nobody has been to your house, nobody has seen the device or the laboratory record, and the choice between courses of action follows from diagnostics performed on the building. What you have here is a reading of what you reported, which is a different thing from a decision and a good basis for making one.
What would change this
- Paired before-and-after measurements across a large set of renovations would quantify how much each trigger typically moves a result — nobody has published that at the resolution a homeowner would find useful.
- A study of retest compliance after mitigation would establish how often silent fan failure actually goes unnoticed, which is currently an inference rather than a measured rate.
- Correcting any answer above. Change an input and the output changes, which is the honest behaviour of something working from a description.
The logic, in full
These are the rules the tool applies — not a summary of them. The interactive panel above evaluates exactly this list, and a build check fails if the two ever diverge. A decision tool whose reasoning you cannot inspect is a black box, and a black box is not authority.
| When | Then |
|---|---|
| Any of: foundation work, new drain tile, sump, or egress window | Retest. Work at the soil interface opens and closes pathways, and the previous result no longer describes the house. |
| Basement finished or converted to living space | Retest. The air balance changed and the exposure changed — the same number matters more in a family room than in storage. |
| HVAC replaced or ductwork altered | Retest. Mechanical changes alter the pressure relationship between the lowest level and the ground beneath it. |
| Windows, insulation, or air sealing completed | Retest. Tightening a house cuts unintentional ventilation and can strengthen the stack effect that draws soil gas in. |
| Mitigation fan replaced | Retest. A different unit performs differently, and the period while the old one was failing may have gone unnoticed. |
| A mitigation system is installed and it has been two years or more | Retest. The manometer confirms the fan is moving air; only a measurement reports the concentration in the room. |
| No system and it has been two years or more | Retest. Two years is short enough to catch drift and long enough to be a habit. |
| Buying or selling | Test now regardless of history. A transaction needs a current measurement under conditions you control, including on a house that already has a system. |
| None of the above and under two years | No retest indicated yet. Note the date of your next one and check the manometer monthly if a system is running. |
What this tool cannot do
- This tool indicates whether to retest. It does not interpret a result — use the result interpreter for that.
- It cannot know about changes you have not told it about, including work done by a previous owner.
- A retest is cheap relative to almost every trigger listed. When in doubt, test.
Related
- What does my result mean? — Your number, read against guidance and against the conditions it was measured in.
- Is my system working? — The safe checks, in order, and where they stop.
- When to retest — Every two years, plus after anything that changes how the house meets the soil or how it moves air.
- Post-mitigation testing — The measurement that records the level once the system is running — and what to do if it is not what you hoped.
- Finished basements — A finished basement raises both the exposure and the cost of fixing it — which is why the timing question matters more than the technique.
- Activating a passive system — Activation is an engineering evaluation of a rough-in you did not watch being built — not simply a fan purchase.
- Radon Testing Method Comparison Dataset — Which method answers which question — and which decisions each one cannot carry.
- Mitigation System Component and Service-Life Dataset — What each part does, how it fails, and whether you would notice.
- All tools — every calculator and decision tool.
Confidence and limits of this page
Every decision resource on this platform states its own boundaries. This is not a disclaimer — it is the part of this tool you should read before relying on it.
- What we knowClaims on this page we stand behind, each traceable to an approved source or to observable structure.
- A two-year retest interval for a house with an active mitigation system reflects standard published guidance rather than our preference.
- Foundation work, basement finishing, HVAC replacement, and envelope air sealing each change how a house moves air or how it meets soil. Those are the standard retest triggers.
- A manometer reports pressure in the pipe. It does not report the concentration in the room, which is why a gauge check is not a substitute for a measurement.
- What we do not knowQuestions you may reasonably have that this page does not answer.
- Whether your house has changed in a way you have not told the tool about, including work done by a previous owner.
- How much any single trigger will move your specific number. The direction is predictable; the magnitude is house-specific.
- What research would settle itWhat it would actually take to answer the above — naming it is the difference between honesty and hedging.
- Paired before-and-after measurements across a large set of renovations would quantify how much each trigger typically moves a result — nobody has published that at the resolution a homeowner would find useful.
- A study of retest compliance after mitigation would establish how often silent fan failure actually goes unnoticed, which is currently an inference rather than a measured rate.
- What we do not claimClaims you might expect to find here and will not, with the reason.
- We do not claim a retest will show a particular direction of change. Tightening a house can raise a reading and mitigation can lower it, but your number is your number.
- We do not claim testing is required. No state we serve requires a homeowner to test an existing home.
- What we cannot independently verifyFacts this page relies on that we could not confirm ourselves.
- The date and conditions of your previous test. The tool reasons from what you enter.
Sources
- U.S. EPA — Radon
- U.S. EPA — A Citizen’s Guide to Radon
- U.S. EPA — Consumer’s Guide to Radon Reduction
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