Radon Testing in St. Louis: When to Test and What 4 pCi/L Means

Radon does not leave droppings, chew through a wall or announce itself with a suspicious noise in the attic. It is an invisible, odorless radioactive gas, which means testing is the only practical way to know the level inside a home.

The U.S. Environmental Protection Agency recommends testing homes for radon regardless of geographic zone. EPA guidance says homeowners should fix a home when the radon level is 4 picocuries per liter (pCi/L) or higher and consider fixing when results are between 2 and 4 pCi/L.

What does a radon test measure?

A radon test measures the concentration of radon in indoor air. The result is commonly reported in pCi/L.

The number is not a score where “close enough” is automatically safe. It is information used to decide whether additional testing or mitigation should be considered.

When should a St. Louis homeowner test for radon?

Testing is especially sensible:

• when buying or selling a home
• if the home has never been tested
• after major renovation or foundation work
• after changes to heating, ventilation or lower-level living space
• when moving into a basement or lower level full time
• after a mitigation system has been installed, to verify performance

Even homes next door to each other can produce different results, which is why a regional radon map cannot tell you the level in one specific house.

Why the EPA map is not a substitute for testing

EPA’s radon-zone map was designed to help governments and organizations target resources. EPA specifically cautions against using the map to decide whether an individual home needs testing.

That distinction matters. A homeowner does not need to prove the neighborhood is “high radon” before testing.

Short-term and long-term testing

Different test durations answer slightly different questions. Short-term testing can provide a quicker snapshot under controlled test conditions, while longer-term testing can provide a broader picture of average exposure over time.

For a real-estate transaction, timing and protocol matter. Follow the instructions for the test method being used and coordinate with the professional handling the transaction if a specific report is required.

What happens if the result is 4 pCi/L or higher?

EPA recommends taking action to reduce radon at or above 4 pCi/L. A qualified radon professional can evaluate the structure and recommend an appropriate mitigation approach.

Around The Clock Pest Control provides professional radon testing in Greater St. Louis. Testing and mitigation are separate steps: first understand the level, then decide what action is appropriate.

What can affect a radon reading?

Indoor radon levels can vary with weather, ventilation, foundation conditions and how the building is operated. That is why test placement and test conditions matter.

Do not move a device from room to room or place it wherever it is most convenient unless the test instructions say to do so. A test is only useful when the protocol is followed.

Frequently asked questions

Can you smell radon?

No. Radon is invisible and odorless.

Is 4 pCi/L a legal limit?

EPA’s 4 pCi/L figure is an action level used in its public-health guidance. Local rules or transaction requirements may differ.

Should I test if my neighbor had a low result?

Yes. A nearby result does not establish the level in your home.

Can a home with a basement have radon?

Yes, but foundation type alone cannot predict the actual concentration. Test the home.

For radon testing in St. Louis, call (314) 303-7240 or request service.

Authoritative source

U.S. Environmental Protection Agency: Radon testing and EPA Map of Radon Zones, epa.gov/radon.