It is a passive radon-resistant rough-in. It relies on natural draft, which the EPA rates at 30 to 70 percent reduction versus 50 to 99 for a fan system. Test the house; if it reads 4 pCi/L or more, adding a fan activates it.
More detail
Look for a 3- or 4-inch PVC pipe rising from the slab through a closet or utility room, often labeled, and for a junction box in the attic, which the EPA recommends for a future fan. Check where the pipe ends: one that stops in the attic instead of passing through the roof is not a working system in either mode. Activation is licensed mitigation work in Ohio (setting aside the owner exemption), and the finished system has to meet the Ohio standards: a fan in the attic, a garage not under living space, or outside; a monitor; labels; and a discharge above the eave and away from windows. On the site's price list, activation runs $700 to $1,200. See passive pipes in new Delaware and Union county homes.