How To Look At A House

McGarry and Madsen's home inspection blog for buyers of  

site-built, mobile/manufactured and modular homes

Do I need a radon test for a house with a radon mitigation system?

Monday, March 23, 2020

Unfortunately, the fact that a house already has a radon mitigation system does not guarantee that the radon level in the home is below the Environmental Protection Agency (EPA) maximum for indoor air of 4.0 pCi/L (pico curies per liter of air). So a homebuyer should go ahead and test to be sure. Here’s three reasons why the indoor radon level may have risen since the system was installed:

1) A mitigation system uses a fan to pull the radon from the ground to a pipe that extends above the roof to keep it from entering the home. The fan’s cfm (cubic feet per minute of air flow) may have deteriorated if it is older, or the fan may no longer even be functional. 

    A simple way to check if the fan is functioning at all is to check the manometer that is required to be installed as part of the system. A manometer is a U-shaped tube on the side of the exhaust pipe at eye level filled with a colored liquid. It is usually located in the corner of a closet in a Florida house, or in the basement of northern house. When the exhaust fan for the radon mitigation system is operating, the air suction will cause the column to rise on one side, and the tube will have inch markings on it so that a viewer can check the number of inches of differential between the equilibrium point of the twin columns in the U-shaped tube. An example is shown below of mitigation system piping installed in a bedroom closet. 

2) The fact that a manometer verifies that the fan is functioning, does not mean everything is alright. Most radon mitigators guarantee to get the indoor air below 4.0 pCi/L when their work is done; but, if the flow of radon from the ground has gone up since installation, the system as installed may not be able to keep up with the higher radon emissions.

3) Also, the EPA standard for any radon system is to check the radon level every two years anyway, and that is not often done by homeowners. So it probably hasn’t been tested in a while.

• • • • • • • • • • • • • • • • • • • • • • • • • • • • •

Here’s links to a collection of our blog posts about “RADON":

• Is a radon test required to sell a house? 

• Should I buy a house with a radon mitigation system?

 Is a radon mitigation fan required to be on a dedicated circuit breaker/fuse in the electric panel?

What happens to a radon test result if the windows were opened, the test device moved, or there was any other evidence of tampering during the test? 

Where do I find the Florida laws regarding radon?

Can I test vacant land for radon before building a house? 

Is radon mitigation possible for a condominium?

Do radon mitigation systems require maintenance?

What is the average life expectancy of a radon mitigation system?  

Do older houses have higher radon levels than new houses? 

Can the seller tamper with a homebuyer's radon test to change the results?

How long does it take to get the results of a radon test? 

Will opening the windows reduce the radon level in a house?

How was it determined that between 15,000 and 22,000 lung cancer deaths each year are caused by radon?

Can a homebuyer do their own radon test for a real estate transaction with a self-test kit?

What is the danger of radon in well water?

What are the symptoms of radon poisoning? 

Does Florida have radon?

Where does radon come from? 

For how many years does an old radon test result remain valid?

Should homeowners get a pre-listing radon test before selling their home?

What are a homebuyer's options when the radon test comes back high (4.0 pico-curies/liter or more)? 

Do granite countertops emit radon?

How can I tell if a house has a radon mitigation system? 

Can a mobile/manufactured home have a high radon problem?

Do I need to test for radon when buying a condominium? 

What does a radon mitigation contractor do to lower the radon level in a home?

How can not testing for radon be an expensive mistake for homebuyers? 

Will the radon test come back sky-high in a house that has been empty and closed-up for months? 

What is radon? Should I be concerned about it?

Should I buy a house with a high radon level? 

What is the average radon level of indoor and outdoor air in America?

What is the operating cost of a radon mitigation system? 

• Does the buyer or seller of a home pay for radon mitigation when the radon test comes back high? 

• What is the probability of having high radon in a Florida house?

• How quickly do I need to reduce a high radon level in my house? 

Does a home inspector check for radon?

What are the problems with underground return air ducts? 

What is the probability of having high radon in a Florida house?

• What factors can change radon test levels up or down? 

• How do I know if a radon mitigation system is working? 

Can I sell a house with a high radon level?

• Does heavy rain change radon levels? 

Does barometric pressure change radon levels?

• Do high winds affect radon levels? 

What radon level is dangerous?

    Visit our RADON page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.

Water Heaters

Water Heater Age

"What Are The

Signs Of..."

Septic Tank Systems

Structure and Rooms

Plumbing Pipes

Termites, Wood Rot

& Pests



When It First

Became Code

"Should I Buy A..."

Park Model Homes


Shingle Roofs




Wind Mitigation

Roof and Attic

"Does A Home


Pool and Spa

"What Is The Difference Between..."




Concrete and

Concrete Block

Metal Roofs


Modular Homes

Rain Gutters

Mold, Lead & Other Contaminants


Older and

Historic Houses

Crawl Spaces

Mobile-Manufactured Homes

Building Permits

Life Expectancy

Clay Soil





Exterior Walls

& Structures


Common Problems

HUD-Code for

Mobile Homes

Garages and Carports

Flat (Low Slope) Roofs

Electrical Panels

Sprinkler Systems

Electrical Receptacle Outlets

4-Point Inspections

Hurricane Resistance

Frequently Asked Questions (FAQ)

Home Inspection

Heating and Air Conditioning

Building Codes

Fireplaces and Chimneys

Inspector Licensing

& Standards

Energy Efficiency

Washers and Dryers



Doors and Windows



Electrical Wiring

Click Below  

for Links

to Collections

of Blog Posts

by Subject

Plumbing Drains

and Traps


Smoke & CO Alarms

Aging in Place

Top 5 results given instantly.

Click on magnifying glass

for all search results.






Air Conditioner & Furnace Age/Size


Electrical Switches





Water Intrusion

Electrical - Old

and Obsolete


Foundation Certifications

Tiny Houses

About McGarry and Madsen



Buying a home in North/Central Florida? Check our price for a  team inspection by two FL-licensed contractors and inspectors. Over 8,500 inspections completed in 20+ years. In a hurry? We will get it done for you.

Moisture Problems

Crawl Spaces