Is radon high in Larimer County, Colorado?

Moderate. The model predicts a long-term basement average of 3.1 pCi/L in Larimer County (about 1.7× the US average of 1.8 and about 1.2× the Colorado average of 2.6). That is in the 2-4 pCi/L range where the EPA recommends considering mitigation. Ranked 32 of 64 Colorado counties.

Should I test for radon in Larimer County?

Yes, soon. With a predicted average of 3.1 pCi/L, many homes in Larimer County will test above the 4 pCi/L action level. Use a short-term kit first; if it reads 2 or higher, confirm with a long-term test or continuous monitor before deciding on mitigation.

What does EPA Radon Zone 1 mean for Larimer County?

Zone 1 - highest potential (predicted average > 4 pCi/L). The zone map dates from 1993 and classifies whole counties. The newer model's predicted average of 3.1 pCi/L does not line up with Zone 1, which is common - the EPA itself says high-radon homes exist in every zone. Neither replaces a test of your own home.

How much does radon mitigation cost in Larimer County?

A standard active sub-slab depressurization system typically runs $800-$2,500 installed nationally; Colorado quotes vary with foundation type (slab, crawlspace, basement), home size and local labor. Get two or three bids from certified mitigators listed by your state radon program or the EPA's find-a-professional page.

Radon levels in Larimer County, Colorado

ModerateEPA Zone 1

Predicted long-term basement average of 3.1 pCi/L (model estimate) across 17 ZIP codes - about 1.7× the US average of 1.8, about 1.2× the Colorado average of 2.6. Ranked #32 of 64 Colorado counties.

Test Larimer County, CO - the EPA says "consider fixing" in this range

The predicted basement average here is 3.1 pCi/L, in the 2-4 pCi/L band where the EPA recommends considering mitigation. Plenty of individual homes in a moderate area test above 4. Start with a short-term test; if it comes back at 2 or higher, follow up with a long-term test or a continuous monitor.

Get a short-term test kit →Or track it with a continuous monitor

Already tested at 4 pCi/L or higher? Find a certified mitigation professional (EPA). A mitigation system typically runs $800-$2,500 installed.

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Predicted (model estimate). The pCi/L figures on this page are long-term area averages from a peer-reviewed national model built on millions of real radon tests (2001-2021). They describe the typical home in this area - not your home, which can be several times higher or lower. The EPA radon zone is a separate, 1993 county-level classification. How the numbers work.

3.1 ± 0.07

pCi/L predicted basement mean (model SD)

2.2 ± 0.07

pCi/L predicted upstairs (above-ground) mean

2.0-3.6

range of ZIP-level basement predictions in the county

What this means for Larimer

The typical Larimer County home is predicted in the 2-4 pCi/L band. The EPA's guidance for this range is to consider fixing, because there is no known safe level and roughly one home in several in a moderate area will test above 4.

Note that the EPA classifies Larimer County as Zone 1 while the newer model predicts 3.1 pCi/L. The zone map predates two decades of test data; where they disagree, we grade on the model but show both. County figures weight each ZIP by its 2010 Census population, so they describe where people live rather than empty land.

Comparable Colorado counties: San Juan County (3.1), Custer County (3.1), Dolores County (3.1), Grand County (3.1). The state's highest is Pueblo County at 4.2 pCi/L.

ZIP codes in Larimer County

Predicted basement and upstairs means by ZIP (model estimate). ZIPs whose land is mostly in this county.

ZIP	Basement	Upstairs	Grade
80525	3.0 ± 0.06	2.1	Moderate
80526	3.0 ± 0.07	2.4	Moderate
80538	3.3 ± 0.06	2.2	Moderate
80537	3.1 ± 0.07	2.0	Moderate
80521	3.4 ± 0.08	2.6	Moderate
80524	3.1 ± 0.06	1.8	Moderate
80528	2.6 ± 0.07	1.9	Moderate
80513	3.1 ± 0.09	2.3	Moderate
80517	3.0 ± 0.07	2.1	Moderate
80549	2.8 ± 0.07	2.2	Moderate
80535	3.2 ± 0.05	2.4	Moderate
80512	3.2 ± 0.05	2.3	Moderate
80536	3.6 ± 0.08	2.6	Moderate
80515	3.4 ± 0.07	2.5	Moderate
80545	3.5 ± 0.06	2.6	Moderate
80547	2.0 ± 0.07	1.8	Moderate
82063	2.7 ± 0.06	2.4	Moderate

If your test comes back at 4 pCi/L or higher

Mitigation is a routine job: a fan-driven pipe that vents soil gas from under the slab to above the roofline, typically $800-$2,500 installed (typical range; local quotes vary). Use certified professionals: EPA find-a-professional. Read the full mitigation guide.

Larimer County radon questions

Is radon high in Larimer County, Colorado?: Moderate. The model predicts a long-term basement average of 3.1 pCi/L in Larimer County (about 1.7× the US average of 1.8 and about 1.2× the Colorado average of 2.6). That is in the 2-4 pCi/L range where the EPA recommends considering mitigation. Ranked 32 of 64 Colorado counties.
Should I test for radon in Larimer County?: Yes, soon. With a predicted average of 3.1 pCi/L, many homes in Larimer County will test above the 4 pCi/L action level. Use a short-term kit first; if it reads 2 or higher, confirm with a long-term test or continuous monitor before deciding on mitigation.
What does EPA Radon Zone 1 mean for Larimer County?: Zone 1 - highest potential (predicted average > 4 pCi/L). The zone map dates from 1993 and classifies whole counties. The newer model's predicted average of 3.1 pCi/L does not line up with Zone 1, which is common - the EPA itself says high-radon homes exist in every zone. Neither replaces a test of your own home.
How much does radon mitigation cost in Larimer County?: A standard active sub-slab depressurization system typically runs $800-$2,500 installed nationally; Colorado quotes vary with foundation type (slab, crawlspace, basement), home size and local labor. Get two or three bids from certified mitigators listed by your state radon program or the EPA's find-a-professional page.

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