Radon in Chester County, PA: ZIP Results and System Costs

Chester County has more radon tests on record than almost anywhere in Pennsylvania. The 36 ZIP codes centered in the county with at least 30 basement tests account for 234,595 basement tests in the PA DEP public data set, and 72,990 of them (31.1%) read at or above 4 pCi/L, by our count through July 2026.

All floors together, DEP's data has 261,523 Chester County tests with 29.3% at or above the action level. That share is lower than in central Pennsylvania, but it is still several times EPA's national estimate of about 1 in 15 homes (EPA Citizen's Guide, 2016), and EPA's 1993 map rates the county Zone 1.

Chester County homes skew large, and HomeGuide's Feb 2026 guide notes sub-slab systems run $1,200 to $2,000 for typical homes and $2,500 or more for large ones.

Licensing and permits

DEP certification is the rule statewide: a paid tester or mitigator must be certified under 25 Pa. Code Chapter 240, and a firm needs a certified responsible individual.

Main Line and suburban townships often run their own code offices; some require an electrical permit for the dedicated fan circuit or exterior pipe. HomeGuide lists radon permits at $25 to $150 where required.

Relocation sales: buyers relocating to the county's corporate campuses often ask for radon results early. Certified testers follow DEP protocols, including closed-house conditions, that a store kit result may not document.

Keep the DEP-filed post-mitigation result with the house records; the next buyer's inspector will ask.

Local conditions

Rock type varies across the county. The north and south uplands are Piedmont crystalline rock, gneiss and schist, and the Chester Valley, the narrow band of limestone that US 202 and US 30 follow past Malvern and Downingtown, is carbonate rock. The far south toward the Maryland line has serpentinite barrens.

ZIP shares spread widely in DEP basement data. Coatesville's 19320 was 45.5% at or above 4 pCi/L across 17,297 tests, Downingtown's 19335 35.4% across 27,835, and Malvern's 19355 36.0% across 15,243. West Chester's 19382, south of the borough, was 17.5% across 20,058 (PA DEP data, our count).

Phoenixville's 19460 sat at 28.1% across 18,784 tests and Wayne's 19087 at 29.8% across 20,167 (PA DEP data). Two homes a mile apart on different rock can differ sharply, which is why EPA says to test every home.

What drives local prices

House size: homes of 2,500 sq ft or more often need more suction or a bigger fan; our calculator applies an est. ×1.25, and HomeGuide's published range runs $2,500 or more for large homes against $1,200 to $2,000 for typical ones.
Mixed foundations: a basement plus a finished slab addition or crawlspace is common in the county's expanded colonials and may need a second suction area (est. ×1.5).
Finished basements: routing pipe through finished space or the garage changes labor; interior routes are an est. ×1.15.
Permit $25 to $150 where required, and a professional retest $125 to $400 (HomeGuide).
A continuous digital monitor, $150 to $300 in HomeGuide's guide, is a popular add-on for families who want ongoing readings.

Common jobs

Sub-slab systems in 1980s to 2000s colonials with finished basements.
Two-point systems for homes with a basement and a slab-on-grade addition.
Crawlspace membrane systems under additions and older farmhouse wings; EPA's 2010 guide put submembrane depressurization at $1,000 to $2,500 in 2010 dollars.
Sale-driven tests and fixes around relocation closings.

From test to fixed, and where we cover

Step 1: test with closed-house conditions, or hire a DEP-certified tester. Step 2: at 4 pCi/L or more, request two itemized bids.

Step 3: check each bid's line items against the calculator. Step 4: retest after installation and every two years (EPA Consumer's Guide).

We cover the whole county: West Chester, Downingtown, Exton, Malvern, Phoenixville, Coatesville, Kennett Square and Oxford, from the Pennsylvania Turnpike corridor south to the Maryland line.

Communities: West Chester, Downingtown, Exton, Malvern, Phoenixville, Coatesville, Kennett Square, Oxford, Berwyn

Before you sign

A high result during a sale is a negotiating point, not a crisis (EPA Citizen's Guide). Get a written bid from a certified mitigator, then size any seller credit to that bid plus the post-mitigation test.

Questions about Chester County

How common is high radon in Chester County?

31.1% of 234,595 basement tests in the county's ZIPs with at least 30 tests read 4 pCi/L or higher in PA DEP data.

Which Chester County areas test highest?

In DEP basement data, Coatesville's 19320 was highest of the large ZIPs at 45.5%, and West Chester's 19382 among the lowest at 17.5%.

Why do big Chester County homes cost more to fix?

More slab area and mixed foundations can need more suction points; HomeGuide's published range rises to $2,500 or more for large homes.

Who can install a radon system in Chester County?

Only a DEP-certified mitigator, under 25 Pa. Code Chapter 240.

Sources

Nearby counties

Rules and fees change; confirm with the state radon office. Price your own system with the radon mitigation cost calculator, read the radon mitigation cost guide, or check any ZIP with the radon levels by ZIP tool.