Indoor Radon Mitigation Effectiveness Calculator

Dr. Mark Wickman headshotMedical review by: Dr. Mark Wickman

Introduction: why indoor radon mitigation estimates matter

When you are planning radon mitigation, the useful question is usually not just whether the number goes down, but how far it may fall after the fan, vent, or depressurization system has had time to work. This calculator turns a starting pCi/L reading, an ACH estimate, a mitigation percentage, and elapsed hours into a post-treatment concentration you can compare against your goal.

Because radon does not behave like a simple on/off setting, it helps to keep the assumptions visible. A strong system, a modest one, and a room with more or less air exchange can produce noticeably different projections, so the calculator is most useful when you want to compare those cases side by side.

The sections below explain which numbers belong in each field, how the page combines them, what the projected concentration means, and where the estimate can be misleading if the real house does not match the model.

What this radon mitigation calculator helps you compare

The calculator answers the homeowner or inspector's version of a forecasting question: if a basement or living space starts at a known radon reading, what concentration might remain after mitigation and normal air exchange have been running for a while?

That makes it easier to compare options such as a weaker versus stronger mitigation setup, or to judge whether a follow-up test is likely to show a meaningful drop from the baseline reading. If your real-world decision is about a basement, crawlspace, utility room, or lower level, use the reading from that same space rather than a different floor.

How to use this indoor radon calculator

  1. Enter Initial radon concentration (pCi/L) with the unit shown beside the field.
  2. Enter Air changes per hour (ACH) with the unit shown beside the field.
  3. Enter Mitigation reduction (%) with the unit shown beside the field.
  4. Enter Hours after mitigation with the unit shown beside the field.
  5. Choose Estimate Post-Mitigation Level to refresh the results panel.
  6. Check the projected pCi/L and the risk percentage before comparing scenarios.

If you are comparing two remediation plans, keep a note of each input set so you can revisit the same radon scenario later and see exactly which assumption changed.

Radon inputs: choosing values that match the room

The calculator's form collects the main factors that shape post-mitigation radon levels. The most common mistakes are using a test result from the wrong room, confusing hourly ventilation with a longer time total, or entering a reduction percentage that is more optimistic than the system can actually sustain. Use the following checklist as you enter your values:

Common inputs for Indoor Radon Mitigation Effectiveness Calculator are:

If a value is uncertain, compare a cautious case with a stronger-performance case. For radon planning, a bracketed range is usually more useful than a single number you might over-trust.

Radon decay formulas: how the calculator turns your inputs into results

In this model, mitigation acts first and air exchange acts over time. The starting radon reading is reduced by the mitigation percentage, and the remaining gas then decays exponentially as the hours pass.

The calculator's core estimate can be written as:

C f = C 0 ( 1 - m ) e - a h

Here, C0 is the initial radon concentration, m is the mitigation fraction, a is the air changes per hour value, and h is the elapsed hours after mitigation began to influence the room.

After that, the page adds a small 0.2 pCi/L offset and converts the adjusted concentration into the displayed risk score:

r = 1 1 + e - ( C f + 0.2 - 4 )

That risk score is a smooth logistic scale centered on 4 pCi/L, so it rises as the projection moves higher and falls as the projected concentration drops.

Worked example: using your own radon measurements instead of a fake sample

Because the result depends on the room you are modeling, a believable example has to use that room's actual baseline reading, mitigation expectation, and elapsed hours. A made-up mix of unrelated values would not tell you anything useful about indoor radon.

Instead of treating this area as a numeric demo, use it as a checklist: confirm the baseline pCi/L, decide how strong the mitigation is likely to be, and check whether the projected pCi/L still lines up with the room you care about.

If the projection seems off, the most influential inputs to recheck are usually the starting reading and the mitigation percentage. Air changes per hour still matter, but in this model they act more like a modifier on the decay curve than a standalone driver.

Radon scenario sensitivity: how the projection changes when one input shifts

Because the calculator uses an exponential model, changing one input at a time is the clearest way to see how the forecast behaves. A lower starting reading leaves less radon to remove, while a higher mitigation percentage lowers the remaining concentration before the decay step even starts.

More elapsed hours give the air exchange term more time to work, so the projection continues to fall as long as the model assumptions stay the same. Higher ACH values also push the number down faster, while lower ACH values slow the decline and keep more radon in the space for longer.

When you compare conservative and aggressive cases, keep every other input fixed so you can see which assumption actually drove the change. Otherwise the comparison stops telling you whether the mitigation system, the room ventilation, or the baseline reading mattered most.

How to interpret a radon mitigation result

The results panel is meant to summarize the forecast, not to dump every intermediate value. The projected pCi/L tells you the concentration after mitigation and decay, and the percentage beside it is a rough risk score derived from that adjusted result.

Use it as a comparison tool, not as a substitute for a follow-up measurement. If two scenarios differ only slightly, the better choice is usually the one whose assumptions you trust most, not simply the one with the lowest number.

If you can say yes to three checks—does the unit fit the decision, is the magnitude believable for the room, and does the output move in the expected direction when you change a major input—the estimate is probably useful enough to compare mitigation plans.

Radon model limitations and assumptions

No indoor radon model can capture every foundation crack, weather swing, soil gas change, or seasonal ventilation pattern. This page is designed to be practical: it keeps the math simple enough to use while still reflecting the major factors that affect a mitigation forecast.

If the projection will inform a health, property, or contractor decision, pair it with a follow-up test or local guidance. The best use of a radon calculator is to make the assumptions visible so you can adjust them, explain them, and compare them honestly.

These starter values are only rough context for a radon mitigation estimate. Use the reading from the room you care about, your best ACH estimate, the reduction you expect from the system, and the hours since it started affecting the space.

Enter the home's radon, ventilation, and mitigation details to project the post-treatment level.