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How can I use an air exchanger to reduce radon?

Soil depressurization is by far the most economical and energy-efficient way to reduce and prevent high concentrations of indoor radon, but what do you do when soil depressurization is not achievable?

Scenarios include: inaccessible crawlspaces (2’ high or less that cannot be sealed and covered); extremely porous soils like karst or old mine tailing fields (which let air flow freely into the home sometimes by the hundreds of cfm); extremely abnormal radon levels (100s of pCi/L).  Certain homes– “Houses from Heck” as we call them in the industry—just don’t respond to the traditional methods of soil remediation.

Sometimes the ‘solution to indoor air pollution is dilution’!  Air-to-air exchangers, HRVs or ERVs depending on your climate, are typically hooked up to your HVAC system.  Air exchangers take the “dirty” air from your home and send it outside, while simultaneously take fresh, clean outdoor air and bring it inside.  These two air channels pass through the air exchanger thermal matrix (from now on I’ll call them HRVs, since that’s what we use in Colorado).  The HRV (heat recovery ventilator) takes the thermal energy from the outgoing air and transfers it to the inbound air.  So in winter conditions, 32-degree air can be warmed as much as thirty or forty degrees before it enters your home!  These units typically only transfer thermal energy (sometimes moisture), but they’ll rarely transfer radon and other contaminants.  


Properly-sized HRVs can prevent radon indoors by replacing all the air inside a home several times per day!!  Outdoor radon concentrations average 0.3 pCi/L in most of the US, so your air exchanger can drastically reduce and prevent indoor radon with these systems running balanced. In extreme cases, you can damper the exhaust (“dirty”) air, which will positively pressurize your home.  If you’ve read my other articles, you know that “your house sucks”.  It sucks in air due to the stack effect and with that brings soil gasses like radon.  

Now think of your house as a leaky balloon.  Instead of sucking air in, with an imbalanced HRV you’re pushing air out through every crack and crevice.  Ex. 200 cfm in, but 180 out, that’s 20 basketballs of air per minute (cfm) that have to find their way out of the thermal envelope of your home.

Conceptually, this is very simple but in practice you need to take into account many other variables so you don’t backdraft appliances or cause other nasty problems.  It is always recommended you use a licensed radon professional and HVAC pro to perform set-up and installation of an HRV as a radon reduction measure.

For energy efficient HRVs, for radon reduction, see the Whole House Indoor Air Quality section of our website here.  Modern HRVs like Fantech’s HERO Series filter out other air contaminants like mold, pet dander, outdoor allergens, and more!

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What type of vacuum pressure does my radon system need?

Before you read this article, have you watched our video u-tubes on Youtube?  Click here

When we get this call by phone, most DIYers think that they need “higher” pressure.  They say their radon system “doesn’t have enough vacuum”.  I’m not sure where this need for vacuum came from, but in my experience, the opposite is true.  You need airflow.  If you’ve read my articles on fan sizing and fan curves, you know that vacuum and airflow have an inverse relationship.  So the higher your vacuum, the lower your airflow.

That’s not to say higher vacuum is always bad.  Sometimes you need a high suction fan to extend your pressure field (PFE) across the entire home.

As always, the best solution is to have a licensed radon mitigator perform proper fan sizing and PFE testing.  Make sure you ask for this service on your inquiry call, as it’s not a standard service all NRPP pros provide.  It may cost a little more, but in the long run, the energy savings will often outweigh the upfront costs.

So, Brent, what is a good vacuum pressure for my radon system? 

Well, more than zero.  That’s all I can say with certainty.  More than zero and less than the functional maximum listed by the fan manufacturer (see fan curves).

What happens if I have no pressure? 

No pressure could mean a few things: your fan is off or has no power; your system has a substantial leak (loose pipe, ripped barrier, etc.); or lastly your manometer is malfunctioning or disconnected.  These are typically easy fixes that any system inspection will reveal quickly.

What if I have pressure, but my radon levels are still high?

This is very common.  This means that you don’t have PFE, so your system is not covering the entire living space.  On suction pit systems, usually you need a bigger pit (see here) or larger pipe (4” rec.).  On crawl space systems, it needs to have a perf pipe or gas mat loop below the barrier to get PFE.  Is everything sealed?  Are there pony walls or multiple crawls?  Are these connected?  Lastly, and least common, is your fan just too small?  Did the contractor put on a cheap imitation fan or a low volume fan to save money?  Was any fan sizing or PFE testing performed or did they “poke and hope”?

If this article hasn’t given you a direction to work with, then it’s time to call an NRPP licensed pro.  Remember, most states have no licensing or training requirements, so just by making it down to this sentence, you may have more knowledge than the radon “pro” you found online.  Be safe; ask for credentials; and test for radon every five years no matter what!

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What is a passive radon system?

Passive radon systems or “radon-ready” systems—as they should be called—are pre-plumbed radon systems for a building. They do not function unless there is a radon fan added to them*. This is why it is my personal mission to remove the term “passive” from the nomenclature. It implies that the system works as is. If you have high radon levels, you’re gonna need a fan no matter what. See this new home my good friend built. He was under the impression that he had a radon system and almost didn’t test! Good thing he knew me. We tested his passive radon system and he had a whopping 11+ pCi/L, nearly three times the EPA action level! He could’ve lived decades in that home thinking he was safe.

Always perform a radon test on a passive home. This is why EPA recommended testing is important and can save your life. You don’t test a home once; you test at minimum every five years.

Why should you build a radon-ready home?

There are many benefits to building radon ready. In my opinion, the biggest benefit is: no loud, ugly radon fan on the side of your house. Yes, we know they’re loud, we know they’re ugly, but they’re better than stage IV lung cancer.

In Zone 1, high-risk states like Colorado, Iowa, or North Dakota, your chances of having dangerous radon levels are higher than having low levels. So if you’re a gambler, you’re betting against the house: literally. Even if you don’t have high radon levels, many homeowners choose to add a low-wattage fan to the system for the benefit of increased airflow under the slab. A dry slab is good for the home’s foundation and it can eliminate musty basement smells.

Other benefits of radon-ready homes are: more energy-efficient radon fans can be installed since you have perfect PFE; smaller fans are quieter fans; fan location is often in garages or attics away from occupants–again quieter; increased home value from having a radon system; and again, radon-ready systems are much more cosmetically appealing than post-construction radon systems.

Passive Radon-ready systems are the future of homebuilding. Don’t get left behind, ask your builder or realtor about radon-ready homes today! PDS offers free system designs at

*Passive radon systems can function in very specific weather conditions due to the stack effect. In North America, these weather conditions do not exist 12 months out of the year, which is why I believe the term is dangerous. If you insist on trying to use your system passively, I cannot recommend a continuous radon monitor more. Watch your radon levels fluctuate with weather patterns and see for yourself.  Passive radon systems include those called out in IRC Appendix F, ANSI/AARST RRNC 2020 and AARST-ANSI CC-1000-2018

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How to choose an energy efficient radon fan

Radon fans are already some of the most energy-efficient air movers in the marketplace.  However, a radon fan runs constantly, 24/7/365. Even the most efficient motors are going to use a lot of energy over their lifetime, so it’s in your best interest to choose an energy-efficient radon fan.

The first and most important way to get an energy efficient radon fan is to have it sized properly.  If you read my post on CFM and PFE, you’ll know that the marketplace drives radon pros to “poke and hope” in order to keep upfront costs low.  “Poking and hoping” may fix a radon problem, but it’s often going to do it with an oversized radon fan.  We’re talking 100+ watts versus 20-60.  Over the lifespan of the fan (5~15 years) that can mean hundreds of dollars in energy usage.

The next thing that an oversized radon fan can do is exhaust conditioned air from the home.  That’s air you paid for!! Radon fans are going to pull from the path of least resistance, and sometimes that means pulling from a tear in your crawl space barrier; or a hairline crack in a slab; or an expansion joint; or a poorly sealed sump; and so on, and so on.  When a large radon fan is moving 100+ cubic feet of air per minute and half of that is coming from inside your home, what do you think that does to your energy bill?  Your HVAC system has to replace that air and condition it to hospitable temperatures.  This is where the real energy costs come into play.

Case studies from leading radon professionals and educators show that merely sealing hairline cracks in a foundation on an average-sized single family home can save over $1,000 over the life of the radon fan.  If you choose a licensed radon mitigator that performs proper PFE testing and radon fan sizing you can’t go wrong.  The upfront cost of using an educated pro will be made up 10X over with the efficiency in your system.

Leading fan manufacturer, Fantech, has also introduced EC motors to the radon marketplace.  EC stands for electrically-communicated.  These motors operate more similarly to DC motors than AC.  They have built-in speed controls and run about 20% more efficiently than AC motors with similar fan curves.  With the speed control, you can also “dial in” the fan to exactly what your home needs.  A radon professional in Minnesota recently used an EC fan to depressurize a home using less than 5 watts of electricity!  EC radon fans can be twice the price of AC fans, however, over the lifespan of the fan you recoup this costs and then some.

For the most energy-efficient radon system possible: use a radon professional that specializes in PFE testing, proper system design, and sealing; and also uses Fantech’s EC fans.  Be sure to sign up for a professional maintenance plan or follow my guide to maintaining your system to keep it running efficiently for decades.

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What do I need to know about Colorado’s new radon laws?

Colorado is one of only three zone 1, high-risk states in the US.  Legislators have seen the data and decided to pass consumer protection and awareness laws.  These laws have no mandates for homeowners, but they do raise awareness of this Class A carcinogen.  If your dwelling touches the soil anywhere in the US, please follow the EPA guidance and perform a laboratory test for radon every five years for the life of your home.

If you live that sweet, sweet van life; then party on!  No radon testing for you.


Is your radon pro licensed?  Check with the state by clicking HERE

In May of 2023, Colorado passed SB23-206 which raises radon awareness for new home buyers and renters.  Click the link above to read more.  The new law requires landlords and home sellers to give written disclosures on the risks of radon to future occupants.  No mandates for testing or mitigation.  More information below:

Does SB23-206 require me to do a radon test?

No, there are no mandates with this law.  Like lead or asbestos, this is an awareness piece designed to educate buyers on the dangers they may face in their new home.

Does SB23-206 force a seller to pay for a radon test?

No, the sellers’ only responsibility is to follow the disclosure notices.  However, if they do not give these documents to the buyer, they can be sued and forced to pay for court costs, radon testing, and mitigation.

When does this law take effect?

Both radon laws are now in effect in the State of Colorado.  Please visit DORA’s webpage or call DORA for more information.


HB21-1195 information below.

In July of 2021, Governor Polis signed HB21-1195 into law*, making Colorado one of only a few “licensed” states. The law is regulated by DORA: the department of regulatory agencies for the state of Colorado. These Colorado radon regulations are part of a sunset law, so it will be in place for ten years. If the citizens demand it’s kept, it will have to be voted into law again in 2031. If its deemed superfluous, it will expire in ten years.

How does the new radon law affect Coloradans?

Colorado’s new radon law is a consumer protection law. Stakeholders in Colorado, including myself, have seen an unprecedented number of consumers with “bad mitigation systems” or having professional radon tests being performed with substandard procedures and equipment.  These systems do not meet industry best practices and put the homeowner in significant danger. Imagine you bought a furnace and it was installed by someone with no training or experience. That furnace could break, maim, or even kill you. That’s why HVAC professionals are licensed. We see the same need for radon professionals.

Radon is a class A carcinogen. It is estimated that nearly two Coloradans die every day as a result of prolonged radon exposure. Radon in Colorado is a serious matter and Colorado Radon professionals have fought to treat it as such. We want to see homeowners safe, and in order to do that we need to penalize contractors acting in bad faith. When a homeowner buys a radon system, it should work. Our hope is that this new Colorado radon law will curb the installation of bad systems and prevent needless disease in our fellow citizens.

What do contractors need to know?

  1. Take and pass an NRPP* accredited course (*National Radon Proficiency Program)
  2. Pass your exam, obtain your national credentials
  3. Register your credentials with DORA
  4. Follow industry code, which includes being licensed and bonded

If you take the reasonable four steps above, you’ll be in the clear. Accredited courses are inexpensive, ranging from $500-2,000, and can often be completed in a few days in person or a few weeks online.

What happens if I don’t get licensed?

Unlicensed radon mitigation and testing contractors open themselves up to criminal liability under Colorado’s radon laws and regulations. Fines and misdemeanor criminal charges can be brought against them immediately. There is no grace period for this act. Licensing starts July 1st, 2022.

How will someone know I’m not following protocol?

Unlicensed or bad work can be reported by anyone. This means anyone can report their competition.

For more information, visit DORA’s radon site, or call RMAARST 720-629-9819

As an industry stakeholder, I’m proud of the steps we’ve taken and happy the State legislature of Colorado agrees with our assessment that we need help. Homeowners still must be savvy consumers and check the credentials of any contractor performing work on their home. However, our hope is that soon enough, contractors wouldn’t dream of going to work without training. Licensed pros are proud of their work. See for more information on how to choose a radon mitigation or testing contractor, and keep up with radon news and safety tips on our blog.

*This page is intended for general informational purposes only and is not intended as specific or legal advice relating to bill SB-23-206, HB 21-1195, or any other statutes, regulations, or ordinances.  Please consult your legal counsel and the State of Colorado to ensure that you are operating within the parameters of the law.  PDS Radon Supply is not responsible for your actions.

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How do I maintain my radon system?

Far too many people think radon systems last forever.  I get calls like this every week: “uh, yeah I need a new radon pump.  It died.”  “When?”  I ask.  “I don’t know, it’s been dead since we moved in in 2006.” Long pause while we contemplate the carcinogen exposure over 15+ years.  “Let’s get you a radon test and an NRPP certified mitigator!”

Have you checked for RED FLAGS yet?  Red flags are a sure sign you should hire a certified pro to fix your system.  CLICK HERE to view the most common RED FLAGS

If you read this blog, you know that the easiest way to avoid dead fans and reduce your lung cancer risk is to test for radon every two years, as recommended by the US EPA.  A digital continuous radon monitor is NOT a replacement for a laboratory test (read why here)

After that, here are some tips for continuing radon system maintenance:

First, check the U tube. We devoted a whole video to this on our YouTube channel. A U tube manometer is a pressure gauge (named for its shape). It reads how much pressure is in the system using “inches of water column.” This is NOT a radon level.  The only “bad” readings on a U tube is zero, equal lines, or max pressure (fan specific).  See my article about radon fan curves for more information. The big thing to watch for is a zero or even reading. Next you want to see if there have been any major changes in pressure. Pressure drops indicate leaks or a dying fan. A significant pressure drop could mean your crawlspace barrier ripped or your PVC pipe is loose. Pressure increases typically mean the system is jammed with something. Did it rain recently?  Has the water table risen? Have you checked your pipe for debris?  

Since pressure drops often indicate a malfunctioning radon system, new standards now require an audible alarm for radon systems. These alarms do not detect radon, but they detect pressure drops (like a dead fan). See our featured products page for radon system alarms!

After checking your U tube, you’ll want to ensure you have no leaks in the system. You can use a smoke bottle to test for rips in crawlspace barrier or sump lids that you cannot see with the naked eye. Check for leaks, especially inside the home, and at all PVC junctions. Are there any cracks in your floor or foundation? Seal them with NovaLink 35 sealant. You will see significant energy savings over time if you have a well sealed floor.

An important part of radon system inspection is to check for debris inside the system.  An easy way to do this is to first cut power to the fan. Then you can remove the fan couplings and pull the fan off the system. Use a flashlight to look up and down the pipe. If you see debris, remove it with a shop vac. Take your fan, while disconnected from power, and flip it upside down, then burp it like a baby. Seriously, manually spinning the fan impeller from underneath and tapping your fan can get rid of all sorts of debris. Leaves, dead bugs, dust, etc. all these things can increase fan noise and impede your system. Once all debris has been removed, reinstall your fan and power it up!

Lastly, perform a radon test! Oh I already said that? Then it must be really important!

Once you’ve done all of the above and your test results have come back under 2.7 pCi/L, your maintenance is complete. Many NRPP licensed pros now offer subscription based radon system maintenance and monitoring. Be sure to ask your local NRPP certified pro if they do follow up testing and maintenance.  Let them take it off your plate and give you peace of mind!

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How much CFM do I need for my radon fan?

We get this question a lot. The true answer is 1+. If you’ve depressurized your soil under your home, you’ve typically solved your radon problem. However, that’s not really what people are asking when they call. They want to know, “what radon fan should I buy?” Without doing PFE testing using professional equipment (pressure field extension), you can’t size a radon fan properly, and radon fan sizing is a complicated process. 

You see, in other industries that use in-line fans–like HVAC–fans work with known inputs and outputs. Duct size, wattage, amperage; all these things can determine a fixed CFM that a fan will run at to do its job. In radon mitigation, there are too many variables to post a consistent CFM. What is your radon level? What are your soils like? Are you using 3” PVC or 4” PVC? Are you connected to a perimeter drain, a crawlspace, a suction pit, or something else? The same fan in any one of these configurations will pull a different CFM every single time. This is why in radon we talk about the fan curve and pressure field.

A fan curve is a chart of airflow versus pressure. The greater the pressure (resistance) the lower the airflow. I like to use the “milk shake versus beer bong” example. A milkshake is thick and hard to pull (high resistance), whereas us college grads know the beer bong is fluid and easy to pull (low resistance). That’s kinda how the fan curve works. Using a manometer like the U tube, or digital professional grade micromanometers, you can estimate your fan’s current CFM by plotting it on a fan curve chart provided by the manufacturer. These charts are also listed on our How to Guides and Data Sheets page.

However, even if you know the CFM, you’ll still need to know how far your pressure field extends to know if you’ve gotten rid of the radon problem. Many radon pros can provide pressure field extension testing these days, however few provide it in every job due to the cost-competitive nature of the business.  It’s cheaper to “poke and hope” and provide a radon-reduction guarantee than it is to do extensive PFE testing on every home.  Ask your NRPP licensed mitigator if they can do PFE testing for effective radon fan sizing that will get the most economical energy use.  You may pay more up front, but having a more energy efficient radon fan will save you in the long run.  You can dive into the specifics of PFE testing by watching the instructional videos at

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Why are radon concentrations higher in the winter?

In short: the stack effect. The stack effect, sometimes called the “chimney effect”, is a term to describe the airflow patterns in buildings. When outdoor temperatures drop, warm indoor air rises inside a building. This in turn pulls colder air from the lower floors. Soil gas is then pulled into the building to replace this air.

In our industry, the joke is: “your house sucks”. What we mean by that is: your house sucks soil air and pulls it inside for you to breathe. Soil air contains radon, a Class A carcinogen.

Ever wonder why radon action month is in January? Simple: the coldest month of the year is typically when radon levels are highest, since the stack effect is strongest. If you’re safe in January, you’re typically safe in August, but rarely vice versa. So January is when you should test for radon.

Radon-222 decays every 3.8 days, so leaving your windows closed all winter is not the reason for the spike. Radon in your home has to constantly be reintroduced. Closed-house conditions can increase levels temporarily, but they will level out. This is why ventilation is not a good long-term solution to a radon problem. First, when radon levels are high enough, even ventilation cannot lower them to a safe level. Second, ventilation without an air exchanger is extremely energy inefficient. That air you just paid to heat or cool, now it’s out the window. Soil depressurization is the simplest, most effective and most energy efficient way to reduce radon levels.

The absolute best way to maintain your radon system is to perform a lab-certified short term or long term radon test every two years during the winter months, when radon levels are highest. This has been the EPA recommendation for over two decades. Just because you have an existing system, does not guarantee it works. The first step is to test and ensure your levels are acceptable.

Read our next article on radon system maintenance for the next steps, but the first step is always test, test, test, especially if we are at a time of year when radon levels are highest!