Updated November 2026 · Data: Pennsylvania DEP radon test and mitigation databases · Sources and method
Pennsylvania DEP has records of 6,965 radon tests in homes with a Horsham, PA mailing address. Of those, 19.7% were at or above the EPA action level of 4 pCi/L, and the median result was 1.8 pCi/L. That share is lower than the Montgomery County figure of 24.6% (Pennsylvania: 33.9%).
These are area results, not your home’s level. Homes on the same street can have very different radon levels. The only way to know yours is to test.
Radon by ZIP code in Horsham
ZIP codes used in Horsham mailing addresses, with at least 50 tests.
| ZIP code | Tests | Median (pCi/L) | At or above 4 pCi/L |
|---|---|---|---|
| 19002 | 93 | 2.5 | 23.7% |
| 19040 | 103 | 2.3 | 22.3% |
| 19044 | 6,692 | 1.8 | 19.7% |
Results by floor
| Floor tested | Tests | Median (pCi/L) | At or above 4 pCi/L |
|---|---|---|---|
| Basement | 4,444 | 2.4 | 26.6% |
| First Floor | 1,319 | 1.2 | 8.6% |
| Slab On Grade | 614 | 1.2 | 5.7% |
| Second Floor | 334 | 0.8 | 4.8% |
| Crawl Space | 49 | 1.4 | 6.1% |
Recent tests (2016 to 2026)
Of the 1,442 tests since 2016, 21.8% were at or above 4 pCi/L and the median was 2 pCi/L.
Radon mitigation in Horsham
- The median reported cost of 54 mitigation systems installed in Horsham from 2022 to 2026 was $1,325 (PA DEP mitigation records).
- Pennsylvania requires radon testers and mitigators to be certified by DEP. Find one in the DEP radon services directory or call 1-800-23-RADON.
- Compare prices in our radon mitigation cost guide.
How to test your home
- Short-term kits cost about $20 to $30 at hardware stores and from Pennsylvania-certified labs (PA DEP).
- Test the lowest lived-in level of the home with windows and doors closed.
- If the result is 4 pCi/L or higher, the EPA recommends fixing the home; between 2 and 4 pCi/L, consider a fix.
More results nearby: Radon in Montgomery County · Radon in Pennsylvania.
Frequently asked questions
Is radon a problem in Horsham, PA?
19.7% of 6,965 radon tests in Horsham homes recorded by PA DEP were at or above 4 pCi/L. Any home can have high radon, so testing is the only way to know.
What is the average radon level in Horsham?
The median of all PA DEP test results for Horsham mailing addresses is 1.8 pCi/L. We use the median because a few very high readings would distort a simple average.
How much does radon mitigation cost in Horsham?
The median reported cost of 54 systems installed from 2022 to 2026 was $1,325, according to PA DEP records.
Sources and method
Statistics use the Pennsylvania DEP radon test database (about 3.4 million tests from 1986 to October 2026), limited to residential and unspecified buildings, for homes whose mailing address city is Horsham. A mailing city can cover several municipalities and ZIP codes. Records can include repeat tests of the same home and some tests after mitigation. Data retrieved November 2026.