This is just an overall question about home radon detectors. Where 10 years ago a topic like this might have seemed off topic (radon detection services sent specimen to labs - charcoal kits). It certainly seems now that the detectors can be accurate.

That is the nature of this question. How does a user get a detector for radon that is accurate? Not talking about bells and whistles but just the accuracy of the radon levels in the home and is there any agency (anywhere in the world) that has tested said accuracy.

Background on this...

Home inspector put a "detector" in the basement of a home I was about to sell. But its readings where high. I knew it was bunk, not because of the high ratings but because of the fluctuations. On day 3 - after it had been high the first two days - I aired out the basement. Opened all windows, big fans, opened the upstairs.

So I expected the levels to drop significantly. Then closing it off on day 4 to see them rise. Nope on day 3 the radon levels where the highest!

Then I am thinking, scam. So let's order the exact same detector from amazon... Comes in a day later. Plug it secretly 2 feet away. Radon levels within range - and vastly different from the other detector - on the EXACT SAME MODEL.

Long story short we had a radon testing service come out and measure. Radon levels were actually very low. Home inspector very embarrassed and I made him refund the buyers. But at same time I am like if I could get a detector for 100-200 I would rather just have them installed in the houses already. But then how do I know if they are accurate.....

  • I think the only way to know if a good tester(of anything) is if the makers show the tester is/has been tested by an independent lab/testing organization.
    – crip659
    Mar 11, 2023 at 19:40
  • 5
    lol cheap chinese testers off amazon marketplace... Mar 11, 2023 at 20:39

3 Answers 3


Well, on the one hand, radioactive decay is a statistical process, so the closer you look, the more variation you have. Longer averaging times smooth out that effect. Here's my last 100 hours with the fan working (in Bq/m3) at one-hour resolution: (100 Bq/m3 is the same as 2.7 pCi/l)

1 hour radon

Same data with 24hour averaging applied (including the 24 before this set affecting the first 24 of this set) - there is an effect of weather on the inflow rates.

24 hour average radon

The model I have claims to be:

Individually calibrated by equipments (sic) which are already calibrated to traceable international standards.

It claims to make 30 tests per hour, reports them locally at 10 minute intervals, and logs the average of those once hourly. The hourly result (and 10-minute result) does bounce around.

I got there by the opposite process - vaguely "overexposed" long-term alpha test, high short term charcoal test, {expletive} I need a way to keep track of this {different expletive}!

For 4 times the price they have a "professional" model, I don't know if that's directly traceable or what, I wasn't going to buy it. Hmm, I think it might have been more water resistant, for one thing - the home model mentions that exposure to high humidity might damage it or permanently alter product sensitivity. I think they also disclaim accuracy after 5 years someplace on their website, I don't see that on the product documents.

My issue, by the way, was a complete surprise - I'm easily 100 feet off bedrock and had no expectation that I'd have the humongous issue I do, especially given that I have no basement, and my county is only moderate concern (Zone 2) according to the EPA radon maps. It's a slab-on-frostwall at or slightly above outside grade level. The saving grace for immediate action was that I put in foundation drains becasue the trench was there - they've never run water, but putting a radon fan on them made a huge difference.

The monitor is far cheaper, and much more responsive*, than running a lot of lab tests, but an occasional lab test is needed to keep it honest, I believe. I'd guess the inspector didn't treat theirs very well and it went out of whack - less of an issue for one that sits in the same house.

*Here, we have my vent pipe frosting over (and being cleared out) when it went down to -15°F a little while back, on an hourly basis. Yeah, that fan is doing some good. Still Bq/m3

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  • I think most testing devices only have a certain time span or need to be tested and adjusted every so often.
    – crip659
    Mar 11, 2023 at 19:34

There are many factors that can affect the rate at which soil gasses come into a house -- shifts in the water table, for example -- so your results may not have been unreasonable.

However, the best answer if you want certified results is to purchase one of the longer-term sampling testers, which then gets sealed and sent to a serious lab for analysis. Used properly these should give you a more accurate reading of exactly what you're dealing with, there's no question of calibration, and they aren't expensive.


Professional devices cost just under $1,000 -$4,000. Any home inspector in a regulated state MUST use an approved device, have it calibrated yearly and conduct dupicates every 10 tests etc.

No device intended for consumers is approved for use by certified or state licensed professionals.

Radon is pressure driven and levels will fluctuate hour by hour and day by day.

Many of my clients have low cost devices and I invite them to place their device alongside mine to determine how their device is tracking.

Recently had a client who bought a home which I mitigated and conducted their own test with a $150 device and insisted my device was in error because their device was " new" and could not be wrong. Well it was wrong.

The inspector should clearly know of the existence of professional monitors and the fact that the inspector used a non appro

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