Radon 101
June 15, 2021
Radon 101
June 15, 2021

Radon 101: What is it? Why do I care?

By now you may know that at Kensa Inspections we have 3 main themes in home inspection:

  1. Safety
  2. Water
  3. Big Ticket Items

“Radon is a radioactive gas that comes from the ground. Learn about the risks it poses, how to test your home for it, how to fix high radon levels, and what guidance is available.

Radon is known to cause cancer. While there are many sources of radiation, radon remains the largest source of exposure. Because we spend so much time indoors, radon in the home represents the biggest concern. The Massachusetts Department of Public Health (DPH) recommends all homes and schools be tested for radon.”

- Massachusetts Department of Public Health

Clearly, radon falls into the first category – Safety.

Where does radon come from?  

When naturally occurring minerals in the earth decay they give off radon gas.  When a house is placed on the ground that gas gets trapped inside, creating the possibility of concentrating the exposure.

It doesn’t matter how old the home is, how it was built, whether the basement is finished, or anything similar.  The thing that determines how much radon is in a home is literally what is in the ground below it.  That’s why your prospective home could have a very low level but your neighbor right next door has higher levels requiring action.  

Radon is odorless, tasteless, invisible, etc.  The only way to know how much radon is present is to test the air.  That’s why we always recommend adding a radon test to your home inspection service.  However, radon gas can dissipate as it rises, so if you’re looking at a condo on the 5thfloor of a large building then a radon test would not make much sense.  But any area from the second floor down should be tested.

Test Types

Here is an overview of the test types.  Both tests require a minimum of 48 hours to be considered a valid sample.


Your inspector places two cannisters in the appropriate location.  These are passive (unpowered) devices that absorb air over time.  The lab specifies a maximum of 54 hours, giving you a six-hour window of time in which to get those cannisters sealed.  Upon completion of the test, it is your responsibility to return to the home to seal the cannisters, place them in the postage-paid box provided and mail them to the lab.  

Mail delivery usually takes a day or two, and the lab takes a day or two to process the cannisters.  After that you can go online to get the test results, and the information needed to do that is included in your inspection report.

For a cannister test, the results consist of one number per cannister, and the average of the two.  That average number is your radon test result.  There is no other information provided.  The cannister test has a lower cost because it gives less information and Kensa does not return to pick up the cannisters. 

Electronic Monitor

In contrast, the electronic monitor is a device owned by Kensa.  We place it the same way as the cannisters, but at the end of the test period we return to pick it up.  

Here is where the monitor has several advantages:

  • You will get a multi-page report the same day the monitor is picked up by Kensa.
  • You get a lot more data.  The monitor takes a reading every hour, giving you a much better overall picture of the radon levels during the test.
  • It also takes several weather-related readings, including temperature, humidity, and barometric pressure.  This information helps you understand whether the appropriate test conditions were maintained during the test timeframe.  For example, if a window was opened it could affect the temperature or humidity.  Weather in general can also impact radon levels, even when proper closed-home conditions are maintained.
  • The monitor also has a motion sensor that will indicate if the device has been disturbed or moved.
  • Another advantage of the electronic monitor is that it has no meaningful time limit on the test duration (a minimum of 48 hours is still required). This gives you added flexibility in the process if needed.  

The passive cannister does not provide any of the above features.

Test Results

If the result meets the EPA threshold for taking action (described as 4.0 pico Curie per liter of air), you can then pursue having a mitigation system installed.  Radon reduction is typically a straightforward process that involves the one-time installation of a specialized ventilation system and subsequent testing to ensure it is working properly.  However, you don’t know if you need to incur that cost unless you have the home tested.

So getting a radon test helps not only with understanding the safety of the home, but also any costs that may be incurred to make it safer.  Kensa provides options that are cost effective and detailed to help you understand the health safety of your potential future home.  

Test Requirements

Please note that there are prerequisites to a successful test which must be maintained for 12 hours prior to and for the duration of the test:

WINDOWS & EXTERIOR DOORS: Keep closed at all levels except or momentary use to enter and exit

CENTRAL HEATING &COOLING: Set to normal, keep between 65° – 80°

WINDOW AIR CONDITIONERS: Operate in recirculation mode only

FANS: Do not operate whole house fans or window fans

OUTDOOR AIR VENTILATION: Do not operate systems that temporarily ventilate with outdoor air for seasonal comfort or energy savings

FIREPLACES & WOODSTOVES: Keep dampers and doors closed and do not use, unless it is the primary heat source

VENTILATED APPLIANCES: Normal operation of clothes dryers, range hoods and bathroom fans permitted (avoid excessive use)

Additional Information

Mass DPH - About Radon in Massachusetts

Mass DPH - Radon in the Home

EPA - Radon Overview

EPA - A Citizen's Guide to Radon