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Community and Q&A

Radon mitigation

Cme4thousits | Posted in Energy Efficiency and Durability on

Two story residence in WV with cold winters, mostly hot, humid summers, HVAC on both floors and lower level mostly below ground level. Plastic under concrete floor and some insulation on basement level walls. House is rather tight construction for the 70’s construction.. Have an installed pipe from below basement concrete floor to above roof with in-line radon fan. Had minimal effect on radon reduction which is at or just above recommended levels to take action. Intend to add exhaust ports in that stack in basement hallway. Would you recommend two entry ports or only one at about 12 inches below the ceiling? Would it be better to have two entry ports, one as mentioned and another at the floor level which would allow closing one during seasonal conditions, like during winter, closing the upper and leaving only the floor port open? Have one prepared for install, and it has a screw-in stop to close it down. Need someone’s recommendation. Thanks.

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  1. GBA Editor
    Martin Holladay | | #1

    A radon mitigation pipe should never have any openings within the conditioned space of your home. The pipe should connect the sub-slab zone (ideally, a volume of crushed stone under the slab) with an exhaust fan installed in your attic or above your roofing. All seams in this pipe should be carefully sealed and airtight. The exhaust fan should, of course, be ducted to the exterior.

    Your plan ("I intend to add exhaust ports in that stack in basement hallway") is not a good one. Don't do it.

    My guess is that either: (a) you don't have enough crushed stone under your slab, or (b) you haven't adequately sealed the air leaks between your slab and your interior space, or (c) your exhaust fan is not powerful enough.

    You shouldn't be doing this work yourself; you should consult a certified radon mitigation expert. Radon is a dangerous cancer-causing gas.

    For more information, see All About Radon.

  2. user-2890856 | | #2

    Radon system should be around entire perimeter with a tee terminating in the open air with the fan . Passive removal without a fan should have 1 vent through the roof for every 1500 sf of slab . this piping should be inside of a stone material deep enough that the bottom and top of pipe are within it .
    As Martin said , do not allow for any leakage inside the conditioned space or the unconditioned for that matter .

  3. Cme4thousits | | #3

    Martin, yes, I am aware that the Rn stack needs to be sealed all the way. But if it did mostly nothing toward reduction of the radon, I thought I might as well make it EOV system since all I have now are bath and kitchen fans periodically, and the HVAC moving the air around. You quote the sub-slab not having enough stone - it has at least 4 inches with plastic sheeting between that and the concrete. Can't quote the cfm on the fan but it was a larger more costly model. Insofar as any cracks in the floor, there were none when the lower level received floor covering years ago (and is now being removed room by room. I expect no cracking. Rn intrusion must be through the block walls and all those exterior walls have 2x4 studs, insulation and wall covering. You quote the exhaust fan is not powerful enough - I believe it is in the upper range but I will have to find my old file. I was going to use the stack as an exhaust system to study the effect, then re-seal it if necessary. The lower level is served by the HVAC and I run a stand-alone dehumidifier, mostly for summer conditions.

    Regarding doing the work myself, I have purchased an H/ERV system and intend to install it myself, but before I do I just read an article on the CERV system from Build Equinox. What do you know about this newer system? It is currently featured in an article in this month's JLC magazine. I am going it alone with studying every article I can including all the posts on GBA and other sources primarily because there are no certified radon contractors within a reasonable circumference and it would cost plenty to contract with someone in Morgantown, WV, etc.

    Richard McGrath also posted. He quotes installing the piping around the entire perimeter. Little late for that with a 70's construction. We did well to get a stack from beneath the concrete sealed all the way through the house w/o bends to 3 feet above the roof. The basement level is 1035 SF, thus one stack should be sufficient.

    Appreciate your comparison of this CERV and using a H/ERV. Thanks.

  4. GBA Editor
    Martin Holladay | | #4

    The three guesses I provided concerning possible causes of your problem were simply guesses (and that's what I called them). The only way to determine what is going on at your house is to visit the house with diagnostic equipment. I strongly suggest that you hire a radon mitigation contractor.

    You may well be right that radon is entering your basement through cracks in your CMU foundation walls. As I wrote in my article, All About Radon, "If the basement walls are made of concrete blocks (CMUs), or if the concrete walls are cracked, it may be necessary to parge or seal the basement walls."

    Here is a link to a GBA article about the CERV equipment that you are curious about: A Balanced Ventilation System With a Built-In Heat Pump.

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