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Radon mitigation and fresh air supply combined?

Griffin728 | Posted in Green Building Techniques on

Hello, if a home tests positive for radon and also would like to have an ERV & fresh air ventilation system, can these things be combined? In other words, can I tie a subslab depressurization system into a the ERV and fresh air system? Alternatively, is there any evidence that a moderate radon problem (4.1) can be mitigated with fresh air ventilation only?

Furthermore, if the radon test came back positive prior to any air sealing or insulation upstairs, is it logical to think that the radon value would increase once the home is further sealed up? The foundation is hollow concrete block with a poured floor, from 1946. It’s a mostly finished basement, but there is one area in the floor where the concrete is broken up for an unknown reason. Are there any basement air sealing techniques that could help with both thermal and air quality control?

Thanks for any info.
Minneapolis, MN

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  1. agurkas | | #1

    I had HRV in the house we bought and it has marginal effect on radon at best. Not sure why previous owner even wasted money on it. Radon in our house was at 11. After spending about $300 on supplies for the complete system, I was down to 2.4 in a week. Mind you, I am trying to mitigate 1500 sq ft basement. I am willing to bet, once I extend the system to crawlspace, I will be down in 1s

    It is fairly easy to put together, especially once you get the hang of glueing PVC. There is a lot of information out there.

  2. fitchplate | | #2

    Radon is heavier than air. It is a gas made of particles that will not be exhausted by an E/HRV unless the E/HRV is at the basement floor level (i.e the low spot where the Radon accumulates; and or the cracks where it enters the building). In other words, it cannot be pulled off the floor by the negative pressure of a fan on a wall. If you try this you will only create air currents that push the radon around the living area at the floor level.

    Radon mitigation solutions using tubing and fans intended to direct the gas (the cloud of radioactive particles) into the air elsewhere serve to transport it and diffuse or dilute the quantity of the radioactive particles for a given volume of air. The radon is still present, just fewer parts per million per liter or air. If you want to get rid of it safely, don’t put it into the air and potentially the breathing zone of people and animals. Instead, send it to a "well" where it is not bio-available.

  3. Griffin728 | | #3

    @Flitch Plate:
    Are you saying there is some form of radon mitigation that does not rely on exhausting to atmosphere? I'd be interested in hearing more about this technique.


  4. Tim C | | #4

    Combining an HRV and sub slab depressurization doesn't make sense. The point of sub slab depressurization is to make sure air under the slab doesn't enter the home; forcing it into the home would make things worse.

    HRV can have modest improvements in radon levels, particularly in tight homes. At 4.1, all you need is a modest improvement (if you really need anything at all, which is debatable if you don't smoke ), so the HRV would very likely be sufficient.

    Radon enters your home from the soil, through the basement. Radon can pass through a solid concrete slab, but it does so very slowly; most of the radon enters through openings or cracks in your basement. Repairing the broken up section of your slab will likely improve your radon levels, which again, considering your already low levels, may very well be sufficient.

  5. fitchplate | | #5

    Ryan ... I am saying that (1) an indirect and elevated exhaust like a typically installed E/HRV will not pick up and disperse radon due to the molecular weight and (2) that radon, no matter how it is captured and transported mechanically, should not be sent into the breathing zone of any human or animal. Conventional radon exhaust systems are not, contrary to the spin and the practice, a safe way to dispose of it.

    Using a radon well with a remote exchaust is better and here is an article that discusses it.

    Putting radon in a well allows for it to be transported away from human space where atmospheric exhausting, if done properly, is outside the proximity of human and animal breathing zones. The method is control pollution by dilution. It does not render radon and parents or daughter nuclides harmless, but it reduces risk of harm by a relative reduction in exposure vectors.

    Blowing it up onto a roof to cascade down the walls of a house and possibly into the bedroom windows is just plain dumb. But some folks here think roof top exhausting is perfectly fine.

  6. charlie_sullivan | | #6

    Air sealing could help or hurt--it could reduce stack effect airflow that brings radon up, but it would also reduce fresh air coming in. But the combination of sealing and providing HRV would likely land you slightly better off than before either.

    Tying the HRV and the sub-slab depressurization together could in principle work, but it's unlikely to work well and could make the radon worse. The balanced ventilation of the HRV is supposed to avoid depressurizing the areas it is exhausting from, so you'd end up pulling air from the other exhaust vents and not from under the slab. And if you did pull air from under the slab, the fact that it's cooler than the other air going through the HRV might degrade the performance of the HRV. So neither the radon nor the HRV functions would be optimal. And whenever the system was off, radon could come in through the exhaust vents.

    As Tim says, "Repairing the broken up section of your slab will likely improve your radon levels." That's probably where most of it is coming in. I'd be willing to bet that you would solve the problem completely if you corrected that. However, sealing up other cracks you can find is also a good idea, and you can also consider a sealer on the concrete (could wait and see on that, after the other work). You might put tubing for a sub-slab venting system in the broken up part before you pour new concrete so you have that available if you decide you need it, but I'm guessing you won't need it.

  7. charlie_sullivan | | #7

    I mean to add...sealing air leaks in the attic will reduce stack effect airflow that sucks air into the basement, including outside cold air and subslab radon-laden air. Sealing air leaks between the basement and the outdoors will actually make the radon worse--stack effect depressurization of the basement will be stronger without those leaks. Sealing air leaks between the basement and the first level would in theory help but there are usually so many leaks there that significant sealing is not practical.

    So the sealing priority is attic and and below grade cracks.

    Flitch, thanks for those interesting references.

  8. Tim C | | #8

    Flitch, where do you think the radon in the soil that doesn't have a house on top of it goes? It disperses into the air around it. There's no reason not to encourage the radon under your house to do the same.

    The weight of radon does not cause it to behave as you describe. If it did, it would never enter our homes in the first place, and continue to sit around in the soil. But at extremely low concentrations, diffusion forces are far more powerful than gravity. The radon will not "cascade" anywhere after leaving an exhaust vent, it will very quickly disperse into the surrounding air.

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