You tested your home and got something like 2.6, 3.1 or 3.8 pCi/L. It is not over the line, but it is not low either. In the Upstate, this is one of the most common situations we hear about, and it is a fair question: do you spend the money or not?
There is no single right answer for every household. But there is a sensible way to decide, and it starts with what the EPA actually says.
What the EPA says about 2 to 4 pCi/L
The EPA's guidance has two thresholds:
- 4 pCi/L and above: the EPA recommends fixing the home.
- Between 2 and 4 pCi/L: the EPA recommends that you consider fixing it.
For context, the EPA estimates the average US home at about 1.3 pCi/L and outdoor air at about 0.4 pCi/L. A result of 3 pCi/L is more than double the national indoor average. The EPA also estimates that radon is the leading cause of lung cancer among non-smokers and the second leading cause overall. The 4 pCi/L action level is a practical line for when action is clearly recommended, not a point below which radon stops mattering.
Why the 2 to 4 range is so common in the Upstate
South Carolina's radon program reports county averages from initial tests through mid-2022. Three of the five Upstate counties average right in this band:
- Greenville County: 3.4 pCi/L average
- Pickens County: 3.0 pCi/L average
- Spartanburg County: 2.6 pCi/L average
Oconee County averages 5.0 and Anderson County 1.7. So if you live in Greenville, Easley, Clemson, Spartanburg or the towns around them, a result between 2 and 4 is a pretty typical outcome. See our county-by-county radon data for the full picture.
Step one: make sure the number is real
Radon levels move around. They change with weather, season and how the house is being used. A single short-term test is a snapshot, and a reading of 3.5 one week could be 2.5 or 4.5 another week. Before you make a spending decision, confirm the result.
Was the first test done right?
- Was it placed on the lowest lived-in level of the home?
- Were windows and exterior doors kept closed for 12 hours before and during the test (normal coming and going is fine)?
- Was it away from drafts, exterior walls, kitchens, bathrooms and direct sunlight?
- Did it run for at least the minimum time on the kit instructions?
If the answer to any of those is no, retest.
Consider a long-term test
Short-term tests run 2 to 90 days. Long-term tests run more than 90 days and give a much better estimate of your year-round average, which is what actually matters for long-term exposure. If your first result was in the 2 to 4 range and you are not under a deadline, a long-term test is the most reliable next step.
If you are under a deadline, such as a home sale, a second short-term test or a continuous monitor can help. Our DIY vs. professional radon test guide covers the options, and our radon testing page explains how we do it.
Step two: weigh your situation
Once you trust the number, these questions usually settle it.
How close to 4 is it?
A confirmed 3.8 is a different conversation from a confirmed 2.1. The closer you are to the action level, the stronger the case for fixing it.
Who lives there and where do they spend time?
If people spend a lot of hours on the lowest level, such as a basement bedroom, home office or playroom, that matters more than a level measured in a room nobody uses.
Are you about to change the house?
Finishing a basement, enclosing a crawl space or doing major foundation work can all change how air moves through the house. It is often easier to plan a radon system before walls and ceilings go up than after.
Are you selling soon?
A buyer's inspector may test. A result just under 4 can easily come back over 4 on a different test. If you are planning to list, see our guide to radon when buying or selling in SC.
How long do you plan to stay?
If this is your long-term home, you get the benefit of a lower level every day you live there.
Step three: compare cost and benefit
A radon mitigation system is usually a one-time install plus a small ongoing electricity cost. Typical ranges in the Upstate:
| Item | Typical range |
|---|---|
| Sub-slab depressurization (slab or basement) | $900–$2,500 |
| Crawl space sub-membrane system | $1,500–$3,500 |
| Combination foundation (crawl + slab/basement) | $2,200–$3,800 |
| Electricity to run the fan | about $30–$300 per year |
These are estimates; your final price comes after an on-site look. Fans are commonly replaced every 5 to 10 years, which is covered in our post on radon fan electricity cost and lifespan. For a full breakdown, see the radon mitigation cost guide.
The benefit side is not something we can put a dollar figure on. A well-designed system typically brings levels down substantially, and many homeowners in the 2 to 4 range decide the one-time cost is worth having a lower number for as long as they live there.
Want to know what it would take for your house? We will look at your foundation, explain the options in plain language and put the price in writing. No pressure if you decide to wait and do a long-term test first. Get a free quote.
If you decide to wait
Waiting is a reasonable choice for some households, especially at the low end of the range. If you do:
- Run a long-term test to get your year-round average.
- Retest after any major renovation, foundation work or HVAC change.
- Retest periodically, since levels can change over time.
- Keep your test results on file for when you sell.
If you decide to mitigate
Most Upstate homes get either sub-slab depressurization or crawl space radon mitigation, depending on the foundation. A typical install takes a few hours, and more complex homes can take up to a day. After the system is running, retest to confirm the level came down. You can see how a job goes from start to finish on our process page.
Frequently asked questions
Should I mitigate if my radon is between 2 and 4 pCi/L?
The EPA recommends that you consider fixing a home between 2 and 4 pCi/L and recommends fixing at 4 or above. Before deciding, confirm the result, ideally with a long-term test of more than 90 days. Then weigh how close you are to 4, how much time people spend on the lowest level, renovation plans and whether you plan to sell.
Can a radon system lower a level that is already under 4?
Yes. Mitigation systems are not only for homes over the action level. A properly designed sub-slab or sub-membrane system pulls soil gas from beneath the house before it gets inside, and it typically lowers levels in homes that start in the 2 to 4 range too. Retest after installation to confirm the new level.