Hello again, folks! I just got the radon test back on my new (to me -- built 1925) house, and at 6.5 pCi/L it came in 1.5x higher than the actionable level. The test has an uncertainty of +/- 15%. The test location was a room in the finished basement where my wife plans to have an art studio. Since the same ductwork serves upstairs and downstairs, I have to assume some of the radon is circulating upstairs as well.

If I were not a former energy auditor, I would slap on a radon mitigation system that exhausts air from the foundation of the house 24/7 and not think one second about where the make-up air comes from. But since I am, I'm trying to decide where to add ventilation to bring in filtered fresh air to replace the radon.

Before I go down that road, though, I wanted to ask whether any of you have had documented success mitigating radon with an HRV or ERV rather than an exhaust-only system. Is that a reasonable approach? Or should I just suck air from the foundation like everyone else?

Thank you in advance for your advice.

Tags: HRV, radon

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There are a couple of important items in your post that started this thread.   

First,  you believe you already have an indoor air quality problem (excluding the radon issues).

Second, your wife is planning on having an art studio in the basement.   No mention of the type of art studio,  oil paints,  sketching, water colors,  photography,  pottery,  metal work?  The type wasn't mentioned.  

Third,  it means the basement area will become a heavily used work space.   Not an area that may have been originally planned only as the location for the heating plant in the house.

For the two reasons above - you should include an HRV/ERV to help ensure the air quality (again ignore the radon) is acceptable. 

Now add-on the radon,    as noted above by others -- trying to solve a radon problem by dilution of lots of air is likely to be a wasted effort.  Several including a few that have lots of experience solving the problem that you described are recommending seeking outside help to plan and implement a mitigation plan.   Companies that have done mitigation/remediation activity in your area are likely to be able to quickly spot and suggest solutions to the common problems that they've seen before.

Radon can come from all kinds of locations - mostly under the slab - frequently from river rock or bedrock that has the "normal" trace amounts of uranium in them.  The radon mitigation folks in your area probably have maps which show the local areas which have a higher risk and the reason for the risk.   I'm an engineer (electrical) and tend to do my own projects.  One of the other writers noted that he'd also helped an engineer that gave up on mitigation activities -- and that was -- because that person focused on the wrong problem.  It's easy to get nerd sniped and go down the wrong path.

What you've described above and previously - suggests that you really need to include the HRV/ERV but not as a tool to mitigate the radon,  but to ensure that the basement AND the rest of the house has a good air quality. The radon mitigation contractor may want to or need to know about plants to install an HRV/ERV such that they can correctly plan their portion of the system.

If this is an older house with ducts in the basement that haven't been looked at for a long time... You may also really want to think about the sizes of those ducts.  If they are from the almost original heating plant - then they would not have been designed for use with an air conditioning system or perhaps a heat pump.  If you are planning on building an art studio in the basement - you really don't want to seal up the ducts and systems overhead --- only to be required that you rip out that ceiling so you can upgrade the duct work.

Hey Ben, long time no see.  Since the old Efficiency Kansas days, I've specialized in radon mitigation.  With the building performance background, installing energy efficient radon systems has been super important to me.  The discussion is interesting because it gives me some ideas to try out.  I'll give you my 2 cents based on my experience and research, as well as, some other folks well documented research.  First, as has already been explained, reducing radon levels is dependent on one of 2 things: 1) ventilation 2) controlling the pressure between the soil and the house. 


If you install a balanced ventilation system, you will basically have to double the ventilation rate to half the radon level.  If you already have a leaky house, this is a terrible idea, as you know.  You want your final level to be as low as possible.  You don't want to 3x your ventilation rate to get below 2.0pCi/L.  Ventilation is more commonly used in tight houses when there are other air quality issues.  The bad thing I have seen with HRV's is that people forget to clean the intake grill, then the house is depressurized and the radon level goes up.  Not to mention HRV's are more expensive to install and operate than even a poorly installed soil depressurization system.  The ERV discussion about radon passing through the core is interesting.  I had never considered that, but I have to think radon would go through.  It's a noble gas and doesn't stick to anything...it can diffuse through concrete if there is a concentration or pressure gradient.

Control building to soil pressure

Pressurization of your basement (not the sub slab zone) will prevent radon entry. You can pressurize the basement with outside air, or with air from the upstairs.  You can supply air from a HRV to a basement and exhaust from the main floor.  Probably the best HRV setup for radon reduction, but still expensive and to purchase and operate compared to a soil depressurization system.  I tried to pressurize a basement (relative to the soil) once in a 1960's house (with upstairs air, no hrv).  It took 900 cfm.  There were just too many leaks between the main floor and the basement to make it reasonable.  And you can't do it if there are any combustion appliances on the main floor.  

Soil depressurization is the most commonly used approach, because it is low maintenance and low initial cost, and if done properly low operational costs.  In theory, all of the air comes from the soil in a soil depressurization system, but in reality that isn't the case, as you suspected.  Omaha, like the middle of Kansas is likely going to fairly tight soils.  If that is the case, you won't have to move much air if you can seal cracks in your slab.  We fix houses regularly where the total air flow is below 10 cfm, using a 15 watt fan.  However, if we don't seal cracks, we might move 70 cfm and still not be able to depressurize the whole sub slab zone relative to the house, with a single suction point. In tight soils, a significant portion of the total air moving through a radon system is going to come from the house, because the path of least resistance is through the cracks, even surprisingly small cracks, like seemingly tight cold joints.

Final thought...it's possible your CO2 problem is coming from the soil.  A Rn system may solve that problem.

Thanks, Chad! Thanks to your comments and many other helpful ones above, I think I'm going to call a general basement contractor who also does radon work rather than a specialist who only does radon. I think the major leak in our basement may be the floor drain, which could also partly explain the VOC readings.Sealing the basement leaks to the ground, wherever they may be, would seem to be the first step (along with getting a professional quality reading of the radon level). Thanks again.

Ben, forgot to mention  - you should not be smelling sewer gas around the drain.  If you are, it could be that the cast iron building sewer has rusted out (very probable based on age of house, if sewer has not already been replaced) and needs replacement (otherwise you would be just draining a lot of your sewage to the ground below your slab and contributing to unhealthy indoor air quality).  You should have a plumber send a camera down the pipe to see shape.  You may be looking at a bigger job, that will require cutting through the slab in places anyway, so that would be a good time to put in the sub-slab radon mitigation. A functioning drain with proper water filled traps will not allow sewer gases to enter home.

Was thinking plumbing drain pipe when responding.  Floor drain makes more sense and totally agree with Brad to add tbl spoon of mineral oil to prevent evaporation of water in trap.

If the VOC and CO2 is coming from the basement floor drain... that's easy to test the hypothesis... move your Uhoo down next to the drain...because of the close proximity to the drain the gases would not have diffused as much and it should go wild for both the CO2 and VOC.

Then pour some water down the drain... to make sure the trap hasn't just dried out... and repeat a few hours later.

Methane from sewers is not something we can generally smell... that sewer gas smell comes from other gases in the system...but it's the methane that is perhaps the most dangerous.

For floor drains that rarely (if ever) see water, pour some mineral oil in the trap to seal out any gases from entering the house. It won't evaporate like water.

OK, I put the uHoo air quality monitor down by the basement drain, and... immediately its CO2 and VOC readings dropped down to baseline. So the drain is not the source of whatever the heck it is detecting, my wife and I are. But I can smell the drain, so it's not off the hook. The trap has water in it because the AC is still running every day, but I'll get it checked out by a pro.

Ben, Using an ERV/HRV works well as I personally know. What your doing are air changes diluting the radon out of the home thus reducing or eliminating continuous Radon exposure. There are variables to consider like which one provides enough cfm for the volume of the home and intermittent vs. continuous ventilation and do you duct it independent of HVAC (which I prefer) or not. Other benefits are improved IAQ and health so good luck!


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