Radon testing and mitigation for Helena homes

How it works

1. Call or send a request

   Tell us your address and your situation: no test yet, a high kit result, a pending sale, or a system that isn't acting right.

2. We connect you

   We pass it to an independent radon testing and mitigation company that covers Helena and Lewis and Clark County.

3. They call you back

   That company looks at the house and gives you a test plan or a written mitigation proposal directly.

Who uses this site?

People who own, rent out, buy or sell a house in Helena, East Helena and the Helena Valley. That includes century-old homes near Last Chance Gulch, ranch houses with basements in town, and newer subdivisions north and east of the city. If the house sits on soil, whether through a basement, a slab or a crawl space, radon can get in. Testing is the only way to find out how much.

How common is high radon in Lewis and Clark County?

Common enough that every house here should be tested. The numbers below come from state and county sources.

• About half of tested homes ran high. In a Montana State University compilation for the state, 52.1 percent of 1,034 Lewis and Clark County tests in the 1997 data and 434 of 836 tests (51.9 percent) in the 2005 data were at or above 4 picocuries per liter (pCi/L).
• The county average is well over the action level. In 2012 the Lewis and Clark Public Health newsletter reported an average indoor radon level of 13 pCi/L in the county, citing the Montana State Radon Office.
• It's in the EPA's top zone. The EPA's 1993 map puts Lewis and Clark County in Zone 1, the category with the highest predicted indoor radon potential.
• Statewide, it's the same story. Montana DEQ says roughly half of Montana homes tested have levels at or above 4 pCi/L, and that the state's geology makes it prone to elevated radon.

None of that tells you your own number. The EPA says its zone map should not be used to decide whether a particular home needs testing, and DEQ notes that homes with elevated levels have turned up in all three zones. Next-door houses can test very differently.

What is radon, and how does it get into a Helena house?

Radon is a radioactive gas produced as uranium in rock and soil decays. You can't see, smell or taste it. Montana DEQ describes local geology as the main factor in how much radon an area produces. Between Helena and Butte lies the Boulder Batholith, a large body of granite (quartz monzonite), and a 1956 study published by the U.S. Geological Survey described uranium in veins in the northern part of it. That doesn't mean every house near the batholith is high, but it is part of why the state takes radon seriously.

Soil gas works its way in through slab cracks, the gap where the floor meets the foundation wall, sump pits, plumbing and utility penetrations, and bare soil in crawl spaces. A heated house usually sits at slightly lower pressure than the soil under it, so it draws that gas in.

Does Helena's winter affect radon levels?

Yes. Helena has long, cold winters. January averages a daily low of 13.5°F, and the coldest night of a typical January drops to about 12 below. With the furnace running and windows shut for months, warm air rising through the house pulls harder on the soil underneath. That's why a closed-house winter test tends to show something close to the worst case. Cold also matters for the system itself: exterior pipes and outdoor fans have to be set up so condensation doesn't freeze at the outlet.

How do I test?

Put a test on the lowest level of the house that is lived in or could be, keep the house closed up during the test, and get it to the lab on time. A short-term kit gives a quick read; a long-term test of 90 days or more gives a better picture of your year-round average. Montana DEQ's Radon Control Program runs a toll-free hotline at 1-800-546-0483 and has offered discounted mail-in kits, most recently during National Radon Action Month in January 2026, while supplies lasted. For a home sale, a radon professional with a continuous monitor is the usual route. More on the radon testing page.

What should I do if the result is high?

The EPA recommends fixing a home at or above 4 pCi/L and suggests considering it between 2 and 4 pCi/L. DEQ advises testing twice before acting on an elevated result, so if your first test was a single short-term kit, confirm it. The standard fix is a sub-slab depressurization system: a sealed suction point under the floor, a pipe and a continuously running fan that vents soil gas above the roof. Details are on the radon mitigation systems page, and crawl spaces are covered on crawl space radon.

Does Montana license radon contractors?

No. Montana DEQ keeps a list of radon providers who hold certification through the National Radon Proficiency Program (NRPP) or the National Radon Safety Board (NRSB), but it states that it doesn't certify those contractors or require proof of certification. Separately, Montana's Department of Labor and Industry requires construction contractors with employees to register. The Montana radon guide for Helena explains what to check and links to every source.

What will it cost?

It depends on the house: the foundation type, how easily air moves through the fill under the slab, where the pipe can run, how many suction points are needed, and whether a crawl space needs a membrane. The radon company you're connected with gives you a written quote after it sees the house. We don't set or quote prices.

Are you a radon company?

No. Helena Radon Removal is a referral service. We connect you with an independent radon company that serves your address, and that company does the testing, design, installation and any warranty work. Before you hire anyone, read our tips for choosing a radon contractor.

Areas we cover

• Helena
• East Helena
• Helena Valley

Planning ahead? Read our Montana radon guide.