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Radon mitigation or ERV for old home with dirt wall basement?

scottiev7 | Posted in General Questions on

Home was built in 1935 and has 5′ dirt and rock walls with a small crawl space above that to the bottom of the upstairs floors which are hard wood when your in the in the basement. Radon measured at 7.7 upstairs above that space. I have a thermopride oil furnace down there also. Radon guys telling me it could cause neg. pressure situation with possible back draft or pull exhaust fumes out of the furnace in the basement area. There is an open walking area the size of a regular sized room where the stairs come down and the furnace and water heater are all easily able to work on

An ERV was recommended for creating a positive pressure situation and hopefully pushing the radon out. They had some plastic put down years ago which is mostly just hanging over the wall and not sealed at all.All vents are sealed off to basement from outside also.

I have very small crawl space and because of the age of the house and the way the house is sitting on rocks and so forth down there, a real good seal will be difficult which is what concerns the guy that I had look at it for the regular radon mitigation. He thinks it will create a whole area of neg. pressure down there, not just behind the plastic where it is suppose to be. Should I have them put the plastic down and do as best they can and then put the ERV in??

Radon guy is reluctant to install a neg. pressure radon removal.

I am confused what to do.. Any suggestion or remedy would be helpful.

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  1. GBA Editor
    Martin Holladay | | #1

    First of all, most basements and crawl spaces are at negative pressure with respect to the outdoors (especially in winter) due to the stack effect. This is normal.

    Second, an ERV can't be used to create positive pressure in your home. A properly installed ERV is a balanced ventilation device -- it exhausts the same volume of air as it introduces, so it has no effect on whether a space is pressurized and depressurized with respect to the outdoors.

    If your radon mitigation contractor is worried that a radon mitigation fan will cause so much depressurization that it will interfere with the draft on your furnace and water heater, then the best solution is to replace these atmospherically vented appliances with new sealed-combustion appliances.

    If you have radon concerns, and you have a dirt-floored basement and crawl space, I don't think there is any alternative to making efforts to seal your dirt floors, using either polyethylene, concrete, or both. I understand that this work can be complicated and expensive, but that's often the case with many jobs that need to be done in an old house.

  2. Expert Member
    Dana Dorsett | | #2

    Where are you located, and how much oil does that beastie burn in a year?

    The very smallest Thermopride puts out about 50,000 BTU/hr and is oversized for a lot of houses. There may be heat-pump options better-matched to your actual heat loads, with lower operating costs and zero backdrafting issues to be concerned about.

    Putting down a non-structural rat-slab with an EPDM or polyethylene vapor barrier under it on top of 4" of 3/4" screenings, with the vapor retarder extending up to the foundation sills, then depressurizing the rat-slab (under the poly) to deal with the radon can work. In a cool climate you may want to insulate both the crawlspace floor & walls.

  3. scottiev7 | | #3

    There is a concrete floor down in the basement. Would not like to replace the furnace at this time due to expense. Looking for the most inexpensive way to get rid of radon. Estimates are coming it between 2800 and 4800 dollars.Two mentioned ERV's and the most expensive guy did not mention an ERV. Because exhaust is gravity feed out, he is concerned of sucking that back into the basement from the furnace. Really do not want to spend more then 3K to get rid of radon. Thank you for all you answers.

  4. GBA Editor
    Martin Holladay | | #4

    In your case, it sounds like the right way to proceed is going to be expensive. It sounds like you have an existing basement slab in poor condition and a dirt-floored crawl space. These areas need to be sealed with new concrete or heavy-duty plastic.

    If you can afford that work, and can install a sub-slab radon mitigation fan, you may find that your existing furnace works fine, without any backdrafting problems. But if there is any hint of backdrafting, the correct solution is to replace the old furnace with a new sealed-combustion model, or (as Dana suggested) switch to an entirely different method of heating your home.

    For more information on radon mitigation, see All About Radon.

  5. scottiev7 | | #5

    The concrete floor is in good condition. The radon is there no matter what furnace is installed. Yes a new enclosed furnace eliminates any back draft problem, but now I have radon still and the expense of the new furnace. I appreciate all you help. It is tough with out seeing my downstairs. I think sealing the walls and crawl space is a good idea which I will have done. The next issue is the ERV or the mitigation fan and piping. How does making a few vents from basement to outdoors for some circulation and a ERV unit cleaning up all that air down there. Hope fresh air will dilute the radon to safe levels.

  6. Richard Beyer | | #6

    Scott Van Der Veer,

    Your situation is exactly what I ran into with my old 1890 home. Radon was 7.2 all of a sudden after years of 2.0-2.6 picocuries. (Spiked after spray foam installation)

    Radon guy's wanted to install 6 mil poly haphazardly over a dirt crawl @ a cost of $2.50 per sq. ft., shove a pipe under the 6 mil laying on the dirt crawl, run a cheap exhaust fan with a final cost of $3800.00 to $4800.00. This was the price to run the pipe outside of the building. Knowing this felt wrong and would look horrible from the outside, I followed my instinct. Since I own more tools than Bob Vila and Norm Abram combined, I had options. Learn the process and install it myself.

    After studying the Rutgers college program for radon mitigation I came to the conclusion this system does not have to be so complicated and costly, because it's not. If your capable of performing your own plumbing you can install this system with ease. By taking the initiative to learn I eliminated the hackers from screwing me out of hard earned money once again.

    In the end, I left the dirt crawl alone (not the case in most homes) as it was left by my former hacker spray foam insulator with a goal of reducing the radon without tampering with evidence and creating back-draft conditions for my furnace exhaust line. My basement space is @1400sq ft. with rubble stone foundation walls. First I mapped out a plumbing plan after studying the radon course. Then the work began.

    I drilled a hole to accommodate a 4 inch PVC pipe through the existing basement slab, removed 20 gallons of sandy soil from beneath the slab with a 3" auger (attached to a drill) and shop vac, installed the pipe just below the base of the slab (no lower), cleaned the cement and sealed around the pipe with backer rod and polyurethane caulk, ran the rest of the pipe straight through the roof boring through closet space, installed a manometer as the instructions called for (basement), installed a Fantech 220 (sealed) radon fan in the attic exhausting through the roof and opened a vent in the basement deck hatch to allow make up air to enter the basement to prevent any worries of back-drafting. For several days the radon level dropped to a steady level which has maintained at a constant @ 2.3-2.6 picocuries in the basement. I know I could get the radon level lower by sealing up the dirt crawl but, that's not an option right now. Best of all the furnace does not back-draft and the radon level is at a safe level in the living space.

    Cost @$1200.00 with college course, all parts, a digital radon meter (long and short term readings) and no headaches of wondering was this job done right. I should also add I have a ERV and dehumidifier in this basement space. The ERV alone did not manage the radon.

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