Radon Level of ZERO?

OK so I recently did a test of a new build that had a passive system but the levels came back at around 10 pCi/l. They installed an active system and I conducted a 96 hour re-test. The re-test came back at 0 pCi/l! I’ve never had a zero reading before and didn’t even think it was possible. The highest recorded was 0.3 with many 0.0 readings (96 hour test). This was conducted with a recently calibrated RS800 with closed house conditions but I’m a little concerned that either my machine fouled up or they had the windows opened or something. No tamper or weird temp or humidity was recorded. Any suggestions?

Of course they’re anxiously awaiting my results as it’s the last thing for the deal…

Background is above zero

The radon rate drops a lot when a system is installed. Don’t second guess the 2nd readings if you didn’t 2nd guess the first. Trust your equipment.

Thanks I was just in a bit of a panic with a very particular buyer and I’ve never had my equipment read so low. I’m running a side by side comparison right now to make sure my machine didn’t crap out. I noticed the readings that were really low (i.e. 0.03 pCi/l) were thrown out by the system and recorded as 0. Anyway, client was cool with it and I even offered a re-test for confidence. I’ll post if anything weird shows up.

Thanks for your input.

What’s the margin of error for the machine? I don’t do radon mitigation but I do own a house that has it lol, and I test for it often and I would be surprised to see it go from a 10 to none or below 1 unless they went overkill on the system

Have you ever performed a “Long Term” test?

As in more than 90 days, no…

The fact that you “test for it often” infers that your climatic conditions change often enough to effect you readings. Run a 9-12 month longterm test to get a true reading of your homes environment. Use that reading as the basis for what you need to do next.

BTW I did an additional comparison test with 2 machines simultaneously and they were within 0.3 pCi/l of each other so I think they’re good to go. I learned the radon mitigation fellow put in a larger fan size and that may have contributed to this very low reading. I did recommend a Sentry Siren and long term testing.

I “tested for it often” ( I meant in general, but I did my home as well) just to build some experience with how tests can be influenced by all the above…sadly my house was a perfect testing ground to learn on lol, but a long term test wasn’t going to happen because mitigation was planned on day 3 lol…I agree that a true long term test would have given the best info but we weren’t going to wait ( especially when 3 weeks after the first test we found out we were expecting ( which turned into twins who showed up 10/20/17))