Radon Zone 2 explained: the 2–4 pCi/L middle band

A radon Zone 2 county is a county where EPA predicts the average indoor radon level will fall between 2 and 4 pCi/L. That is the middle of the three zones and the least useful one to act on directly: it sits above the level where EPA says to consider fixing and below the 4 pCi/L action level, so the label describes a house that might need nothing and might need a system. The number from your own test is what breaks the tie.

What Zone 2 actually predicts

The zone map assigns every county one predicted average, built from indoor measurements, geology and aerial radioactivity surveys. Zone 1 is above 4 pCi/L, Zone 2 is 2–4, Zone 3 is below 2; the zones section sets out all three. The thresholds follow the action level, which is why Zone 2 starts at the point where EPA first suggests considering a fix.

The prediction is a county mean. A county that sits at 3 pCi/L in the model contains houses at 1 and houses at 9, and the mean says nothing about which is which. Reading the label as a forecast for one address is the mistake the zone map overview spends most of its length correcting.

Why the middle band is the hardest to act on

At 6 pCi/L the decision is easy: confirm, then mitigate. At 1 pCi/L it is also easy: keep the report and retest later. Between 2 and 4 the answer depends on details the county average cannot see — whether the basement is finished, whether anyone sleeps there, whether the reading came from January or July, and whether the first test was even placed correctly.

EPA’s language reflects that. The agency says to consider fixing in the 2–4 band, and to fix at 4 or above. “Consider” is doing real work: it is a risk judgment about a specific house, not a threshold that trips automatically. The action level explainer covers how the guidance is written.

Test the house before you reason about the zone

Start with a short-term kit at $15–$45 including lab analysis: two to four days, house closed for 12 hours before and during, detector at the lowest lived-in level and four feet off the floor. The testing section covers placement, and the kit comparison explains what each device measures and what it does not.

That first result sorts the house into one of three buckets. Below 2 pCi/L, you have a report and a two-year calendar entry. At or above 4, you have a reason to confirm and price a system. Between 2 and 4, you have a reason to test again with a longer instrument.

The order matters. A homeowner who starts with a mitigation quote in a Zone 2 county is usually buying a system before knowing whether the house needs one, and a $1,200 install is an expensive way to answer a question a $35 kit already answered.

Reading a single result near the line

A short-term reading of 3.6 or 3.9 pCi/L is not a verdict. Three things move a four-day number.

Season is the largest. The stack effect is strongest when indoor and outdoor temperatures diverge, so a January test in a cold climate tends to read higher than a July test in the same room. A house that reads 3.8 in summer may read above 4 in winter and below 3 in spring.

Placement is the second. A detector next to a draft, in a closet, or on the second floor measures something other than the basement air. Basement readings are the ones that matter when the basement is lived in.

Device uncertainty is the third. Every measurement carries an analytical and sampling error, and EPA’s own guidance on measurement reliability treats a result near a threshold as a range rather than a point. A single 3.9 is compatible with a true annual average on either side of 4.

The practical response to all three is the same: run a long-term kit before deciding.

The long-term test that settles it

A long-term kit costs $20–$50 with analysis and stays in place for 90 days or more. It integrates the seasonal swings into one number, which is exactly what you need when the question is whether the house’s year-round average crosses 4 pCi/L. Place it in the same room as the first test, keep the house in normal use, and leave it alone.

A 90-day kit started in late autumn is the strongest version of this test, because it includes the coldest months when radon indoors peaks. If the long-term result comes back at 5 pCi/L, the case for mitigation is settled. If it comes back at 2.2, you have a defensible reason to wait, retest in two years, and spend nothing.

When “consider fixing” becomes fixing

Four conditions push a Zone 2 house from watching to acting.

The confirmed number sits in the upper half of the band, roughly 3 pCi/L and up, on a long-term or repeated short-term test. The basement or lowest level is used daily, so exposure is not theoretical. The house has an obvious pathway — a bare slab, an open sump, a crawl space without a membrane — that a system would close. Someone in the house is at higher risk from long-term radon exposure, which is a conversation for a physician rather than a contractor.

When those line up, price the work from the foundation. EPA’s band for a fan-based sub-slab system is $800–$2,500 installed, averaging near $1,200, and the cost guide explains what moves a job within it. A crawl space runs $1,100–$3,000 because the dirt floor needs a sealed membrane first. The systems section covers the hardware.

Running cost is minor next to the install: a fan draws 60–90 W, and an 80 W unit uses about 701 kWh a year, roughly $127 at the August 2026 US average of 18.16 cents per kWh.

Zone 2 in a sale or a new build

No US state requires a radon test at sale. Illinois, Minnesota, New Jersey, Pennsylvania and Iowa require disclosure or a pamphlet, which means a Zone 2 address may come with paperwork and no measurement. In a purchase, treat a missing test as a reason to order one during the inspection period rather than a reason to assume the house is fine.

For new construction, Zone 2 is the awkward case for passive radon-resistant construction. The system costs $500–$1,500 built in, and the case for it is weaker than in Zone 1. If the builder offers it and the budget allows, it is cheap insurance and can be activated later with a fan for $300–$900. If not, test after occupancy and mitigate if the number calls for it.

A decision sequence for a Zone 2 house

1. Short-term test at the lowest lived-in level. Record the dates and confirm closed-house conditions.
2. Below 2 pCi/L: file the result, retest in two years.
3. At or above 4 pCi/L: confirm with a second test or a certified measurement at $150–$250.
4. Between 2 and 4 pCi/L: run a long-term kit for 90 days through winter.
5. Act on the long-term number, then verify any system with a post-install test and retest every two years.

The zone tells you the question is live. It cannot tell you the answer, and in the middle band the honest tool is time — 90 days of it, in the room where you actually breathe the air.