Archive for November, 2020

Radon Sensor Review: Airthings Wave Plus versus RadonEye RD200

November 28, 2020 3 comments

This is a continuation of this post.

Here we compare the radon readings from the Airthings Wave Plus and the RadonEye RD200 devices. For this comparison two Wave Plus sensors and one RD200 is used. There are no calibrated reference readings to compare against so conclusions are drawn based on cross-checking and environmental factors that can be controlled like opening windows and changing device locations. Conclusion: the RD200 device is fast and obtains good accuracy within an hour whereas the Wave Plus devices as described require >7days for accuracy and in practice produces readings that are confusing.

Beyond active radon mitigation, getting fresh outdoor air inside is effective at reducing indoor radon levels. The Seattle area is in a national Zone3 radon region which means <2.0 pCi/L levels are the average. However radon levels vary house to house significantly due to local geography and house construction and so it should not be assumed radon levels are guaranteed safe in even low to moderate risk areas. And even when radon levels aren’t high enough (>=4.0 pCi/L) to warrant active radon mitigation or strongly suggest mitigation (2.0 – 4.0 pCi/L) there’s still health value in keeping them as close to outdoor air levels as possible (0.4 pCi/L) as there is no known “safe” level of radon.

Our 1974 home is built into a hill with a daylight basement. When we moved into this hour earlier 2020 we brought our single Airthings Wave Plus sensor and started seeing slightly higher radon readings of 0.5 – 2.3 (average 0.8) pCi/L on the upper sleeping floor. Our prior slab-on-grade house was drafty and had no basement so it saw radon levels like 0.0 – 1.6 (average 0.6) pCi/L. While our new house didn’t have levels high enough to warrant mitigation, having a young family and spending significant time indoors working from home meant it was worth to double-check the data. At this point we acquired a second Airthings Wave Plus to get dedicated readings from the basement office. While it showed slightly higher readings than the upper floor I was still finding the radon readings from both Wave Plus devices to be non-responsive to the significant amount of fresh air being brought in with open windows and fans. This was suspicious as bringing in fresh air to dilute stale air is an effective way to reduce radon levels (page 11). At this point I started to question the Airthings Wave Plus radon readings altogether.

Here we see many times where closing windows and turning off fresh outdoor air causes the Wave Plus radon readings to strangely plummet and vice versa where opening windows and turning on fans causes the readings to skyrocket.

I started looking around for other data-logging radon detectors and found the RadonEye RD200. It uses the same radon sensor as their RadonEye Pro professional device which comes with certifications. Both devices are factory-calibrated and tested for accuracy of <10% at 10pCi/L in less than 60 minutes where as the Airthings Wave Plus is noted as only being +-10% at 5.4pCi/L in 7 days or +-5% at 5.4pCi/L in 2 months. That is the RD200 is significantly faster than the Wave Plus for radon measurements and in practice seems to operate even faster.

As soon as we purchased a RadonEye RD200 its readings made much more sense. Windows being opened and fans being turned on to bring in fresh air caused radon levels to drop and closing up windows correspondingly allowed them to rise back up.

Opening a window and turning on a fan causes fresh air to dilute stale air causing radon levels to drop. Closing windows and turning off air cycling causes radon levels to rise.

At this point, with a responsive radon measurement device on hand I paired it with the basement Wave Plus and moved them about the house to attempt to cross check their radon readings and to try to determine any patterns.

Devices were kept in the same room’s location from 24 hours to up to 4-days

LocationRadonEye RD200Airthings Wave Plus
Basement office0.08 – 1.84 (0.73 average)0.32 – 4.73 (1.09 average)
Basement bathroom0.14 – 1.28 (0.75 average)0.95 – 1.59 (1.27 average)
Basement den0.14 – 1.66 (0.85 average)0.24 – 1.11 (0.62 average)
Basement garage (very drafty)0.05 – 0.43 (0.26 average)0.46 – 0.59 (0.51 average)
Upstairs bedroom0.14 – 1.54 (0.63 average)0.14 – 1.24 (0.66 average)
Devices were side-by-side and readings were from same timespan.

Some conclusions from the readings:

  • Opening a window and turning on the fan to bring in fresh air into a room is very effective at reducing radon levels. When this is done open another window on the other side of the floor to allow air to vent out.
  • Upstairs bedroom averages were 0.5 – 0.75 pCi/L lower than corresponding basement readings
  • Airthings Wave Plus radon measurements move in directions opposite to expectations. Not a good device for short-term readings to determination if radon mitigation is working. Possibly adequate for medium-term analysis on the order of days/weeks.
  • Airthings Wave Plus can randomly record spikes in the data. When the spike in the chart below occurred I received a notification on my phone for exceedingly high radon levels at a pCi/L level higher than the data recorded. I recall it being a very suspicious value like 100+ but it didn’t occur to me to take a screenshot of it.
The recorded radon levels from the RD200 (green line) are much more responsive to fresh air mitigation and whether windows are opened or closed

Both devices detect radon levels independently of other environmental factors. Radon readings from the Wave Plus and RD200 devices were evaluated against other environmental factors to check if they were being biased. Initially it seemed like the RD200 was responding to temperature (a drop in temperature also showed a drop in radon) but this was checked by leaving the device in a temperature-stable location and there the readings still fluctuated based on air freshness. In the end both device’s radon readings appear to be largely determined based on how much stale air there is and existing sources of radon.

Radon readings compared to Temperature (F) and Humidity (%)
Radon readings compared to CO2
Radon readings compared to VOC

Two Airthings Wave Plus devices will read potentially very different radon values. Airthings only notes +-10% accuracy to occur within 7 days. In most of my household measurements between the two devices located on different floors the values have generally been no where close to each other. But by the end of the fourth day after keeping the devices next to each other we do see the values to start to move closer to each other so it’s possible with additional time they’d align. However it’s clear that Airthings Wave Plus radon sensors do not have the monitoring resolution to be responsive unlike the RadonEye. Being responsive is very helpful when testing different mitigation strategies.

Two Airthings Wave Plus sensors side by side read different radon values. Possibly corrects itself when left to calibrate after at least 7 days.

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Airthings Wave Plus vs RadonEye RD200

November 16, 2020 1 comment

We have a couple of Airthings Wave Plus devices to keep track home air quality metrics like CO2, TVOC (Total Volatile Organic Compounds), and radon levels. While the non-radon readings like CO2 and temperature have been accurate and responsive, over time it was noticed that the radon readings did not reflect environmental changes like the opening of windows to cycle air. Instead the radon readings seemed to raise and lower at their own volition, as if the readings were being pulled from some other house or based solely on the weather. I chalked it up to rain just having an outsized effect on radon levels but given I still wanted to track down potential radon sources (like was our open basement floor shower drain a source?) I knew the Wave Plus devices weren’t likely to be much help.

Given that a RadonEye RD200 was purchased to compare against the Wave Plus. It touts itself as being “>10x more sensitive and accurate than other home radon detectors“. The Airthings Wave Plus apparently takes 4 Radon readings an hour. The RadonEye device itself takes readings every 6 minutes (10 readings an hour) though the data export from their app only yields data in 1-hour increments, with each data point being a 60 minute moving average. Neither the Wave Plus or the RadonEye are certified, but the RadonEye Pro is “AARST-NRPP and NRSB” certified and both the Pro and non-pro version tout very similar features, including the sampling rate and touted accuracy, so there’s a non-trivial chance that the non-pro version is as good as the Pro version just without the certification backing it up. In fact, in an email exchange with Radon Corp it was confirmed that the non-pro RD200 device is factory calibrated just like the Pro version though the difference being you can’t re-calibrate the RD200 after purchase. (also it’s expected to remain accurate “for 7 years”).

The primary sensor location for testing is a basement office (11’x13′) with a single small 1’x4′ window that opens in half for a 1’x2′ opening. There’s a small but strong 9″ fan (Honeywell HT-800) inside the window bay that pulls in enough fresh air to easily turn over the room’s air several times over the course of the day with fresh air. The entire bottom floor is a daylight basement set into a steep hill where the backside of the house is fully below ground and the front side of the house is fully above ground. We live in a Zone3 radon region (where average indoor levels are noted as <=2 pCi/L) but more locally the risk is actually moderate. Both of the sensors are on a small shelf near each other about 4′ from the floor and 1′ away from the wall.

With only a couple of day’s worth of results to compare against the Wave Plus so far the RD200 seems to be much more responsive and seems to track well against changes in the environment. For the last 48 hours here is an Excel rendering of the data exported from RadonEye’s app and the same timeframe via Airthing’s

The RadonEye RD200 clearly follows whether there’s fresh air being introduced.

And a summary table for that same 48 hour period comparing the low, high, and average pCi/L readings for the two devices:

Low pCi/LHigh pCi/LAverage pCi/L
Airthings Wave Plus0.32.21.1
RadonEye RD20000.171.450.7

So if you squint the numbers are in roughly the same ballpark, it’s not like the Wave Plus measured pCi/L > 4 and RD200 measured <0.5. But still, the Airthings measurements are about 41-55% higher at any given time and seems to be moving with a 12-hour moving average or… something. For instance at 5pm today 11/16 the RadonEye noted levels of 0.17pCi/L, after a full work-day’s worth of a fan pulling in fresh air. However Airthings recorded it at the highest level for the 48hour period at 2.2pCi/L!

To be updated after a full week’s worth of data… See here for the update.

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