Radon mitigation

Last summer we borrowed a radon tester from a friend and left it in the basement for a few weeks. We didn’t expect a problem because the old house, 400 feet away, had pretty low levels of radon in its basement. So we were alarmed to see the levels rising to around 18 pCi/L, more than four times higher than the amount the EPA says is its “action level”. We bought our own radon tester and it confirmed the high readings.

Then we moved the tester upstairs and things seemed pretty good all summer and into the fall: the level was around 2 pCI/L. But after the weather got cold and we closed up both the basement windows and the house windows, the level started rising and eventually reached 7.0 without any sign of slowing down.

So clearly we needed to do something. Radon mitigation systems typically cost up to $1500 to install, and consist of a pipe that runs from under the basement slab to a point outside the house, with the airflow driven by a fan that is constantly running. Usually the fan and much of the pipe are installed inside the house, hidden in attics or closets or behind walls, with the final length of pipe protruding through the roof. But this kind of installation would be difficult and ugly in a house like ours, with exposed wood everywhere and no attics or drywall. The idea of cutting yet another hole in the metal roof was too daunting, as was the idea of hiring a contractor to do the work.

So we decided to install the radon system ourselves. We had already done plumbing and electrical work on the house, so this new project didn’t seem out of the question. Fortunately, there’s a small company that offers free advice and sells all the parts (aside from the pipe) needed to install a system.

We already had a hole in the basement slab that was originally meant for a shower drain, and which went right down to the crushed ledge gravel under the slab. This was the perfect place to start the pipe. We capped off the opening and ran the pipe through the cap, caulking liberally to avoid leaks.

Then the problem was deciding where to run the pipe up the side of the house. We wanted the pipe to terminate at least 12 inches above the roof. But we didn’t want to cut a hole in the roof, which would have been necessary at the eaves because of the large roof overhang there. Also, running the pipe up one of the eave sides would subject it to pressure from snow sliding down the roof. So running the pipe up a gable end would fix those problems. But running the pipe up either of the two gable ends closest to the hole in the slab would require boring a 4-1/2 inch hole through a beam, and that seemed too extreme, as well as potentially unsafe.

The most workable solution was to put the pipe up the gable end of the one-story section, which has a walkout basement. This required installing a 40 foot length of pipe along the basement ceiling:

The pipe is sloped slightly downward towards the slab hole, so that any moisture will tend to head back to the gravel. Then the pipe exits the basement through a hole bored just above the basement door:

Outside the house sits the fan:

The fan pulls air from the pipe in the basement and sends it up the exterior pipe. The top of the pipe has two 45 degree joints that allowed us to avoid having to cut a hole in the roof:

The electrical work was straightforward and simple.

The system definitely works: after about five days of running the fan continuously, the radon level in the basement dropped to .9 pCI/L. As an experiment, we turned off the fan for 12 hours, and the level climbed back up to 1.4. So the fan needs to stay on.

This leads to one problem with the system, aside from the electricity usage: the fan noise. It’s hardly noticeable in the bedroom, at the opposite side of the house. But in the dining area, a few feet from the fan, the noise is a bit annoying. To help with the noise, we installed a Leviton RTF01-10Z capacitive ceiling fan control in series with the fan, and the “high” setting greatly reduces the fan noise and speed. But we’ll need a week or two of experimentation to know whether the reduced speed also reduces the system’s effectiveness at removing radon.

Update: The ceiling fan control works. The “high” setting reduces the airflow to about 1/3 the maximum, according the manometer we installed on the pipe, and after several days of running the fan at this speed, the radon level continues to drop slowly.