How to choose a radon test kit

Radon is a naturally occurring gas that moves out of soil and rock and into houses through the foundation. It has no smell and no taste, so a measurement is the only way to know a level. That measurement costs $15 – $50, and the system that reduces a high level costs $800 – $2,500. The order those two numbers go in is the entire point of this page.

What actually decides this purchase

Four things separate a test that gives you a usable number from one that gives you a number you end up repeating.

Short-term vs long-term

Short-term kits sit 2–7 days and give a fast screening number. Long-term kits run 90+ days and capture seasonal variation, which is the more accurate picture of your actual exposure.

The two answer different questions. A short-term kit answers "does this house need a closer look", and it is the right instrument during a real estate transaction where a 90 day result would arrive months after closing. A long-term kit answers "what am I actually living in", because radon swings with soil moisture, frost, wind and how tightly the house is closed up. A common sequence is a $15 – $35 short-term screen now and a $25 – $50 long-term test running in the background afterwards.

Lab fee included

Many charcoal kits advertise a low price and then charge separately for lab analysis. Compare the total, not the shelf price.

Read the listing for the phrase "lab fee included" before comparing prices. A kit at $12 with a $35 analysis charge costs more than a kit at $30 with analysis and return postage in the box. Check the expiry date on the charcoal too, since detectors have a shelf life and a stale one returns a result the lab flags rather than reports.

Continuous monitors

A digital monitor costs more up front but reports continuously for years with no lab fees, which is useful after mitigation to confirm the system is still working.

A monitor at $150 – $280 passes the cost of about five to eight kits, and then keeps reporting for years. It is the practical choice if you are tracking a borderline result across seasons, if you want to see what happens when the basement door stays shut for a week, or if you have a mitigation system and want the fan failure to be visible. Look for a model that displays both a short-term and a long-term average, because the long-term number is the one that matters for a decision.

EPA action level

The EPA recommends acting at 4.0 pCi/L or above. Test before spending anything on mitigation, and test again afterwards to confirm the system works.

The number is the whole decision. Above 4.0 pCi/L the EPA recommends fixing the house. Between 2 and 4 pCi/L it recommends considering a fix. Below 2 pCi/L the recommendation is to leave it alone. Retest after any mitigation work and after major renovation, foundation repair or a change in how the house is ventilated, since all of those alter the pressure relationship between the soil and the living space.

Test before you spend anything else

Below 4.0 pCi/L the EPA recommendation is to retest rather than mitigate. A kit at $15 – $35 can therefore save you a $1,500 system, and it is the single clearest cost sequence in home maintenance. Any contractor conversation that starts before you hold a number is a conversation about a house nobody has measured.

That works in both directions. A result of 1.2 pCi/L means the recommended action is to leave the house alone and retest every couple of years or after work that changes the foundation or the ventilation. A result of 2.8 pCi/L puts you in the range where the EPA suggests considering a fix, and where a long-term test is worth running before you decide, because a single winter week can read high. A result of 8.0 pCi/L is a clear recommendation to mitigate, and at that point the number has done its job.

Radon levels also vary house by house on the same street, which is why a neighbor's result, a county map or a contractor's regional average is background information rather than your number. State radon programs publish the mapped zones, and those zones tell you how likely elevated readings are in your area. They cannot tell you what is in your basement.

How to run the test properly

The instrument matters less than the placement and the conditions. A kit run in the wrong spot returns a real measurement of a place you do not live in.

1. Choose the lowest lived-in level. A finished basement counts. An unfinished basement you use as a workshop or laundry counts. A sealed crawl space you enter twice a year does not — in that case test the floor above it.
2. Close the house 12 hours beforehand. Windows and exterior doors stay closed except for normal entry and exit, for the 12 hours before and the whole test period. Running a whole-house fan or an open-window night mid-test produces a low reading that means very little.
3. Place the detector correctly. Two to six feet above the floor, at least three feet from exterior walls, windows and doors, and away from drafts, heat and high humidity. Keep it clear of the sump, the dryer and any supply register.
4. Leave it for the full exposure period. Short-term kits need 2 – 7 days depending on the model. Note the start and stop times on the card, since the lab needs both to calculate a concentration.
5. Mail it the same day it comes down. Charcoal detectors keep adsorbing and desorbing after the test window, so a kit that sits in the car for a week returns a degraded result. Long-term alpha track detectors are far more forgiving on this point.

Two more timing notes. Avoid running a short-term test during a severe storm or unusually high winds, both of which shift the pressure relationship between the soil and the house. And if the result will inform a purchase decision, some states require the test be performed by a licensed measurement professional at $150 – $300 rather than by either party to the sale.

Reading your result

Results come back in picocuries per liter, written pCi/L. Three bands cover the recommendations.

• 4.0 pCi/L and above. The EPA action level. The recommendation is to fix the house, and a mitigation system runs $800 – $2,500, with a national average near $1,500. A crawl space system, which requires sealing the ground surface first, runs $1,500 – $4,000.
• 2 to 4 pCi/L. The EPA suggests considering a fix. This is the band where a long-term test earns its $25 – $50, because a year-long average tells you which side of the line you actually live on.
• Below 2 pCi/L. No action recommended. Retest every two years, and after any work that changes the foundation, the slab or the ventilation.

If a short-term result comes back high, the useful next step is a second short-term test rather than an immediate contract. Two short-term results that agree give you a defensible basis for spending, and they cost less than a tenth of the system.

Testing after mitigation, and what the system costs to keep

Always retest after mitigation, because it is the only proof the system works. A sub-slab depressurization system is a fan, a pipe and a manometer, and the manometer only tells you the fan is moving air. It says nothing about the concentration in the room. Schedule the post-mitigation test for two to four weeks after the system goes in, with the house closed as before.

The ongoing numbers are modest and worth knowing before you sign. Radon fans last 5 – 10 years and cost $200 – $400 to replace. Electricity for a continuously running fan runs $75 – $200 per year. A fan that has quietly stopped is invisible from inside the house, which is the strongest argument for a continuous monitor at $150 – $280 in a mitigated home: it turns an annual chore into a reading you glance at.

Retest every two years even with a working system, and any time you finish a basement, replace a furnace, seal a crawl space or have foundation work done. Each of those changes how air moves between the soil and the rooms above it.

• Radon mitigation cost — system types and installed pricing
• Crawl space encapsulation cost — the sealing a crawl space system depends on
• Basement waterproofing cost — where waterproofing and radon work overlap
• Basement repair cost — fitting this into a wider basement budget
• Crack in a foundation — sealing the entry paths radon uses