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Radon fan location: outside via drain tile?

SwitchgrassFarmer | Posted in General Questions on

Per the oft cited recommendation, we installed a passive radon pipe in our home during construction. It’s piped off the foundation Form-A-Drain and incorporates a top of the house area with electrical circuit and enclosure for the radon fan. We are now at the point where it probably makes sense to install that fan. In fact the fan is here ready to be plumbed in. (I have good reason to believe the passive radon pipe vent works, at least to some degree; certain times of the year you can see frozen water vapor near its output.)

Our radon results hover around 4 to 6 pCi/L. This a composite of a series of readings the last three years that include 2 short term charcoal tests from Air Chek, 2 four month long canister tests from AccuStar, and a Corentium real time radon meter running since last November 1st. These measurements all taken on the ground floor.

Important note: The aforementioned tests were largely taken during the winter where it is generally assumed radon is at its worst due to stack effect, wet and frozen soil outside, and general sealing up of the house. A spot check with the Corentium late summer / early fall indicates levels below the 4 pCi/L recommended action level. One of the late spring charcoal tests corroborates that trend coming at 2 pCi/L. (I have a late spring first floor test charcoal test that, as expected for an upper level, was much lower, .7 pCi/L.)

So now to the question, do I plunge forward and put the fan in the existing radon piping, with a radon alarm nearby in case it were to fail? Or, do I install it outside?

As it turns out, due to a change in how we wanted the land graded near our home, our Form-A-Drains daylight into “wells” near the home. My intention was to fill the wells with 2B stone, and then bury them as we do our final landscaping near the house. Here is the thing, one of those wells happens to have a conduit direct to the electric panel. Not only that, this well has connectivity to a separate perf drain run under the center of the house. Ostensibly that secondary perf drain, buried at ground level under a few triaxles of clean 2B stone, could perform significantly better than the main Form-A-Drain as a radon exhaust pathway.

I found an example of a somewhat similar outdoor radon venting scheme. Anyone have experience with same?



PS 1: Yes, I am aware of the “hire a radon expert” clause.

PS 2: I spend 99 percent of my indoor time on the 1st floor. One of the cats does sleep downstairs a few hours a day though.

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  1. charlie_sullivan | | #1

    As I understand it, the option to try to install a fan on the footing drain is a second best option to try to solve a problem without installing a proper sub-slab system. So I would be surprised if that was a better option than using the proper radon vent you have installed. Am I missing a reason you are considering that?

  2. SwitchgrassFarmer | | #2

    Charlie, right now the radon vent riser runs off the eastern foundation footing Form-A-Drain. This portion of Form-A-Drain exists for roughly 1/2 the house including a center bearing wall. (We are built into a hill.)

    What I was pondering was whether to use (or also use) the additional sub-slab perf drain that I put inside the western walk-out portion of the foundation, where the footing level is approximately 3' lower.

    The "air-flow" connection between those two footing levels is mainly via the gravel in-fill underneath the entire basement slab.

    I may be answering my own question as I write this. The suction path to the existing radon vent from our western underslab section isn't as direct as it could have been.

  3. GBA Editor
    Martin Holladay | | #3

    There are several issues here.

    1. One possible approach is to do nothing, since your radon levels are relatively low. For most of the year, your radon levels are safe. Perhaps you could increase the ventilation rate (not the radon exhaust rate) during the coldest weather of the year if you are worried.

    2. You shouldn't consider your suggested approach unless someone remembered to install a check valve (called a "reverse flow valve" in the illustration you linked to) in the drain pipe leading to your dry well.

    3. Remember that a radon exhaust fan can't be located inside your home's thermal envelope.

    -- Martin Holladay

  4. GBA Editor
    Martin Holladay | | #4

    I wouldn't worry about the occasional very slight depressurization that occurs when your HRV goes into defrost mode. For more information on this issue, see Exhaust-Only Ventilation Systems and Radon.

    If you do end up installing a radon fan, you should install an exterior model. That's the standard solution in homes without a vented attic. For more information, see All About Radon.

    -- Martin Holladay

  5. SwitchgrassFarmer | | #5

    That Exhaust-Only Ventilation Systems and Radon article is spectacular. (Chuckled at the "retired engineer ...did his own radon mitigation system..." section.)

    Yea, when Charlie Sullivan asked if there was some other reason I was considering not utilizing "the proper vent you have installed" I should have told him the fan location/envelope issue.

    I just ordered four more AccuStar test kits. Going to put two on the ground floor and two on the first floor and let them run for the full year term. Will check back in March/April 2018!

  6. SwitchgrassFarmer | | #6

    Martin, good thoughts. Talking this through is providing me some clarity.

    Per your issue list, in reverse order.

    3. Well you know this is one more of the downsides of a SIP home versus one with a traditional attic (as you favor). The radon fan location is underneath the SIP roof panels and so inside the home envelope. Hence my view the only way that could work would be to install an active radon alarm near it in case the fan or associated piping were to fail.

    2. I still have the capability to install the check valve if warranted. No matter what I do I have to reconcile this issue since my footer drains are "daylighted". My original thought was to fill the wells with stone, cap the risers, and then put a layer of soil over the top. Hopefully that would minimize the amount of "fresh air" short circuiting into the footers.

    1. Been looking over EPA's radon measurement protocol while I have my morning oatmeal. I thought I had enough measurements in quantity and timeframe to establish a direction, but I was likely wrong.

    EPA says: "An initial short-term test, which lasts for two to 90 days, ensures that residents are informed quickly should a home contain very high radon levels. Long-term tests, give a better estimate of the year-round average radon level. The closer the long-term test is to 365 days, the more representative it will be of annual average radon levels. "

    Based on what I have seen so far, I am fairly certain lower spring/summer/fall levels would average out the higher winter levels. My yearly average probably will be well below the 4 pCi/L action level.

    BTW, as to increased ventilation. Of course I run an HRV, but interestingly I think it may not be of the style most advantageous for a home where radon might be an issue. During subfreezing weather 5 out of 40 minutes the unit goes into defrost mode where it shuts off the supply fan. Consequently the house is somewhat depressurized at that time, exactly what you wouldn't want. Fortunately last winter I installed an outside wall relief damper that opens during those defrost cycles

  7. Expert Member
    Michael Maines | | #7

    There is nothing special about the 4 pCi/L threshold that makes it a safe level. It's like saying that two or three cigarettes a day are perfectly fine. Natural outdoor levels are around 0.4 pCi/L. I recommend power venting when over 2 pCi/L.

  8. Expert Member
    Dana Dorsett | | #8

    The EPA remediation levels are only a recommendation, not a regulation. In Europe the regulated limit is 6.7 pCi/l and the risk is still "in the statistical noise". In reality anything in single-digits can be considered "pretty safe".

    The notion that the increased risk from inhaling 4 pCi/l air vs. .04 pCi/l air is like "...two or three cigarettes a day..." is not supported by any well controlled statistical study. Other background sources of ionizing radiation unrelated to radon add up to about the same dose as that, and life has evolved with the same order of magnitude of background level of radiation, with mechanisms that give considerable tolerance to radiation levels that low.

    For some perspective, the OSHA limit (which IS a regulation) is 100pCi/l for 40 hours per week. In a (7x24=) 168 hour week that's equivalent to a continuous 40/168 x 100pCi/l = 24 pCi/l six times the EPA recommended level for remediation. Does that mean the OSHA limit is the same increased risk of smoking a pack a day? (Don't think so!) An additional 4-8 pCi/l of radiation rate from the radon decay in the indoor air doesn't produce a measurable increased risk- it's largely theoretical, unlike the increased risk of smoking a couple of cigarettes per day. But when you're at 40 pCi/l (which is above the OSHA dose limits, and several times the background radiation dose) the risk is coming out of the statistical noise and definitely worth taking action on.

    The EPA model (as well as the European regulation) uses a linear extrapolation from risk studies of underground miners at exposure levels between 100x & 1000x the 4 pCi/l, which isn't really valid. It's known that at low levels the human health risk from radiation isn't linear, and 4 pCi/l in the air would represent only fraction of the total background radiation. The increased radiation hit airline personnel take from cosmic rays flying several hours per day at 30,000' of altitude is large by comparison, with an enhanced risk that's very difficult to tease out of the statistics. They aren't required to wear radiation protective clothing or use cumulative radiation dose badges, even though some may hit annual dose levels comparable to or higher than some nuclear plant workers.

    There is some reason to believe you're damaging your body's radiation resilience by smoking it may make you more susceptible to the radiation damage of 4pCi/l air, but there isn't a good way to tease out the radiation damage from the chemical damage of the smoke in the statistics.

    Where you live makes a much larger difference in the total background radiation dose per year than 4pCi/l vs. 0.4 pCi/l indoor air. A resident of Denver at 5000' gets ~80% more total exposure than an average Boston resident, primarily due to the increased cosmic rays even at that fairly modest altitude. That's a bigger difference in radiation hit than the 0.4 vs. 4. Is living in Denver instead of Boston the risk equivalent of a couple of cigarettes per day? (That should be pretty easy to prove, if it were true.)

    A resident of the state of Kerala in southern India gets something 10,000% (100x) the annual radiation dose of a Boston dweller (despite much higher ventilation rates in the typical Indian house) due to the prevalence of radioactive thorium in the soil there. Is that like smoking 10 packs/day? Should they declare the entire state a hazard zone?

    The health risk from cooking smoke in the villages is higher in Kerala than the background radiation risk- they have bigger problems to worry about. And if your radon decay radiation rate of the air volume in your house is in single digits pCi/l, so do you.

    BTW: There is some evidence in the scientific literature from large scale epidemological studies that the correlation of home radon levels and lung cancer is NEGATIVE between 1pCi/l and 50pCi/l (lung cancer rates fall with increasing radon levels in homes up to about that level, implying that the radon may be providing a protective effect at 50pCi/l in a home environment ) and rises back to background rates when the radon level hits 80-100 pCi/l. The mechanisms for that effect aren't 100% clear, but the size of mujltiples studies showing a similar effect have been large enough that it can't be ignored, even though the effect is small. It could be that applying abatement measures even at OSHA limit levels measured in homes could be hurting more than it's helping, but if it turns out that it's hurting the effect is pretty small, and the potential affects on other cancers is unknown. Spending any money at all to duck from 6 pCi/l to under the EPA recommended 4 isn't necessarily warranted, but it's probably pretty safe to drop it from 40pCi/l into single digits, and "worth it" if it makes you stop worrying about it. Getting it under 4 may make it easier to sell the house if the EPA never updates it's recommendations to reflect the data from broader studies on residents rather than miners.

    The dose you get breathing low-radioactive air in a house while sleeping or binge watching Orange is the New Black is very different from the dose somebody gets digging ore or operating equipment laboring in a mine, even at the same radioactivity levels, and the risk factor from dust inhalation in a mine is very different from that of the residential couch spud or hard-sleeper. There's very little that's "right" about model the EPA came up with for the recommended mitigation level. It needs a serious overhaul.

    Granite countertop radiation, anyone? :-)

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