Money spent in the wrong order buys anxiety instead of answers. This page sorts the two steps — measurement and mitigation — into the order that fits your actual situation, including when skipping straight to quotes is the rational move.
The question underneath the question
How firm is the number you already have? A test conducted under closed-house conditions — windows shut, normal HVAC, device on the lowest lived-in level — is one somebody would find hard to challenge. A transaction test performed by a licensed measurement professional is harder still. A kit that sat on a windowsill for two days in mild weather is a real reading with a known caveat attached.
If you have not measured at all yet, that is the cheaper problem — what a radon test kit can and cannot settle covers when a DIY result answers the question, when a transaction needs a credentialed measurement instead, and the six conditions that quietly make a kit result unusable. When it does come time to hire, how to find and verify a radon professional explains why the credential decides who may do the work and the distance does not.
Everything else follows from that, and it is not a question this page can answer about your test — which is why the comparison below describes both paths and what each would establish rather than telling you which one is yours. The testing library covers twelve specific concerns, each with what your result still supports regardless.
Measuring further, or acting on what you have
Two paths, described rather than ranked. Which one fits depends on how firm your existing number is, what deadline applies, and how the space is used — and the first of those is a judgement for somebody who can examine how the test was produced, not something this page can assess.
Measure further before deciding
Another measurement — a second short-term test under controlled conditions, or a long-term detector left in place for ninety days or more — before committing to any work.
What it would establish
Whether the first reading holds up under conditions somebody deliberately controlled, rather than under whatever conditions happened to prevail.
For a long-term test, what the household actually lives with across seasons, which a short-term reading cannot describe.
A second data point, which is what turns one number into a range you can reason about.
What it would leave open
Everything about the building. A measurement says what the concentration was; it says nothing about how soil gas is entering or what would reduce it.
Whether the device or laboratory behind either reading was in good standing. That is a question for the programme that certifies them.
What any eventual work would cost, which follows from a design, which follows from diagnostics nobody has run yet.
Situations it commonly fits
A reading close enough to a threshold that weather or conditions could plausibly have moved it either side.
A short-term test run in mild or cooling weather, where the heating-season figure is likely to differ.
A test where closed-building conditions are uncertain, or where the placement is now known to have been unusual.
No deadline — nobody is waiting on an answer, so ninety days costs nothing but time.
If it turns out to be the wrong path here. Time, and continued exposure at whatever the true level is while the measurement runs. Where a transaction deadline applies, the cost can be the deadline itself.
Act on the number you already have
Treating the existing result as the basis for a decision, and moving to diagnostics and proposals from professionals who visit the building.
What it would establish
What is physically happening under and around the building, once diagnostics are run — which no amount of further measurement would reveal.
What the work would actually involve here, and what it would cost, both of which follow from a design rather than from a reading.
A verified outcome, if the work proceeds and a post-work measurement follows it.
What it would leave open
Whether the original reading was representative. Acting on it does not confirm it, and a system sized against an unrepresentative number is sized against the wrong figure.
What the house reads across seasons, unless a long-term measurement happens alongside or afterwards.
Whether the result would have been challenged had somebody examined how it was produced.
Situations it commonly fits
A reading well clear of a threshold rather than close to it, where a second measurement would be unlikely to change the decision.
A long-term result, which already describes the annual picture a further short test would only sample.
A transaction deadline that a ninety-day measurement would not survive.
A household that would want the work done at this level regardless of where a second reading landed.
If it turns out to be the wrong path here. Money spent designing around a figure that a controlled re-measurement would have revised. The work is not wasted — a system that reduces levels reduces them — but the specification may not match the house.
What actually decides it
Four factors, none of which this page can evaluate for your house. Where the first is genuinely uncertain, that uncertainty is itself the answer to what to do next.
How firm the existing number is
When it matters. Always, and it is the factor that most often settles the question — a reading nobody would challenge behaves very differently from one that sat on a windowsill.
What it would establish. Whether a second measurement would be likely to change anything, which is the only reason to run one.
What deadline you are working to
When it matters. When a transaction, a move, or a contractual date constrains the sequence, because a ninety-day measurement fits inside very few of them.
What it would establish. Which options remain available at all, before their merits are worth comparing.
Who lives there and how the space is used
When it matters. When the same figure would be weighed differently for a storage basement and for a room somebody sleeps in every night.
What it would establish. How much the exposure duration matters relative to the concentration, which is a household judgement rather than a technical one.
A professional review of how the test was produced
When it matters. When the firmness of the existing number is genuinely uncertain and you would rather not guess at it.
What it would establish. Whether the reading is defensible, which is a judgement for somebody who can examine the placement, the device, and the conditions — and not one a website can make.
Test types, compared honestly
The three below measure the same gas over very different windows, which is why two honest results can disagree without either being wrong — what to make of two devices that disagree is its own question, and a common one once a second test comes back.
Method
Duration
Strengths
Limits
Short-term kit (charcoal)
2–7 days
Cheap, fast, fine for a first look
A snapshot — radon swings day to day
Continuous monitor (CRM)
48+ hours
Hourly data, tamper-aware; the transaction standard when run by licensed pros
Costs more; still a short window
Long-term test (alpha track)
3–12 months
Averages across seasons — the truest picture of exposure
Slow; useless inside a deal window
When a retest earns its delay
One short-term result between 2 and 8 pCi/L, with no deadline: confirm, then decide from the average.
Suspect conditions (windows open, test near a draft, device disturbed): redo it properly.
Staying long-term at 2–4: a long-term test gives the average that band deserves.
When a retest wastes your window
Licensed CRM result inside a transaction: the clock is running; quotes are the productive next call.
Results well above 8: confirmation almost never changes the decision.
Serial retesting in search of a lower number: that’s shopping for comfort, not measuring a house.
And after mitigation: testing returns
The sequence ends where it began — with measurement. A post-mitigation test verifies the system actually lowered your number, and a retest every couple of years (EPA’s standing guidance) confirms it keeps doing so. Mitigation without verification is a fan and a hope. See how systems work and what the numbers mean.
Common questions
Can I go straight to mitigation without any test?
You can — some owners installing during a renovation, or buying a home where every neighbor mitigated, choose to — but you’d be fixing an unmeasured problem, and you’ll still need testing afterward to verify performance. The economical order is almost always: cheap test, informed decision, verified fix. A contractor who discourages pre-testing is selling hardware, not outcomes.
Why did winter and summer tests on my house disagree?
Seasonal physics. Closed-house winter conditions concentrate radon; open-window shoulder seasons dilute it. Both tests measured truly — they measured different operating modes of your home. For action decisions, weight the closed-house result or run a long-term test; you live in winter mode for a large share of the year here.
Are the $15 hardware-store kits accurate enough to trust?
For screening, yes — properly used charcoal kits from reputable labs are how millions of homes get their first number. Their weakness is protocol sensitivity: placement, duration, and closed-house discipline are on you. Treat a clean kit result below 2 as reassuring, anything elevated as a prompt for a confirming test or quotes, and any sloppy deployment as void.
The seller offers “their” old test result. Is that my number?
It’s information, not diligence. Conditions, seasons, and even the house itself (renovations, HVAC changes) may have shifted since. Illinois requires sellers to disclose known results, which is why you have it — but buyers ordering their own licensed measurement during inspection remains the standard, and no serious agent will advise skipping it to save a modest fee.
Already holding an elevated result?
Then you’re on the mitigation step — get free quotes from independent licensed contractors and decide with real numbers.