Compatibility of formaldehyde sensor (Sensirion SFA40) with AirGradient One Indoor Monitor

Quic · February 25, 2026, 8:12am

Greetings,

Recently purchased a DIY indoor AirGradient One after seeing online reviews and I’m pretty happy with it overall. Easy to assemble etc. (although the bottom stand was a bit tight once it locked in and one stand nearly snapped when I tried to remove it to adjust something inside the case).

Only issue is that one reason for the purchase was to measure formaldehyde (HCHO/CH2O), and unfortunately the product doesn’t seem able to do that at present. However, AirGradient seemed a bit more reputable than run-of-the-mill sensors, and I like the extensibility and open-source support the company and product has.

Looking through some older topics on this, the Sensirion SFA30 sensor was mentioned for measuring formaldehyde, but it seems to have been recently deprecated in favor of their SFA40 sensor. I don’t know much about these circuit boards and the software, but squinting at some pictures of the sensor, it seems to have four pins at the back, just like the VOC sensor the AirGradient One shipped with.

Would anyone happen to know if this sensor can fit into the the current VOC sensor “socket”? And since this measures in ppb rather than the 0-500 index which AirGradient One uses for VOC, would there be any changes in the firmware required?

If it’s plug-and-play or “plug and play and flash some new firmware”, it should be easy enough to set up. Anything more complicated than that (e.g. editing code) might be a little challenging, though…

Thanks!

Altair_AirGradient · February 25, 2026, 1:51pm

Hi @Quic! We haven’t tested the SFA40 yet but from what I see I don’t think it is “plug and play” compatible with the current version of the AirGradient ONE. We are working on a redesign of the AirGradient ONE and trying to make it more modular so more sensors could be added as needed. I will share this with the engineer we have working on the redesign so this can be taken into consideration.

Thanks a lot for the feedback!

Quic · February 25, 2026, 3:57pm

Thanks for weighing in before I got one that wouldn’t fit
Yes, the modularity of such devices, though costing a bit more than single-purpose sensors, will definitely find a niche among the BIFL (buy it for life) community, since they have the flexibility to swap sensors as needed (Framework’s modular USB C inserts come to mind). If there’s standardization of some sort (e.g. connectors) in the sensor industry, that’ll make it even easier.

Looking forward to the re-design when it comes!

Altair_AirGradient · February 27, 2026, 4:28am

Hi @Quic - I want to correct my earlier reply here as I gave you incomplete information before.

After taking a closer look, it actually seems that the Sensirion SFA40 can be connected to the current AirGradient ONE v9 board, although it is not a direct plug-and-play replacement for the existing VOC module.

If we look at this version here that you shared: instead of fitting directly into the socket, the SFA40 could be connected via the VOC sensor header using male pin connectors / jumper-style leads there.

However, this would require firmware modifications, since the AirGradient firmware currently expects VOC data and the SFA40 outputs formaldehyde concentration so sensor initialization and data handling would need to be added.

So in short: hardware connection appears feasible.

Thanks again for raising the question and apologies for the earlier confusion on my side.

Tommi_S · March 11, 2026, 4:30am

So, is that so that in short there is no chance at the moment to order a HCHO addon to newest Airgradient One? The AI informed that that would be possible with at least SFA30 module, but it’s not? HCHO is very important indoor gas to be measured, much more useful than VOC, I agree.

Peter_Crona · March 12, 2026, 7:51am

I’m also quite keen on adding SFA40. But I guess one can’t just send new things to the API and have them displayed in the app/dashboard? So even if I got it to work and updated the firmware, I would only be able to use these values on-device? Alternatively, send formaldehyde as TVOC, and lose the SGP41 TVOC in the app/dashboard?

Beyond formaldehyde being an important pollutant, I like that the sensor seems fairly selective and is factory calibrated, so one will (hopefully) get a good idea of the absolute concentration. And perhaps that can sometimes even aid in interpretation of the relative VOC index.

I’m just waiting for the prices to go down a bit and might give it a try, although not sure yet if on my AirGradient or on a separate Arduino.

Reason for hoping prices will go down soonish is: https://sensirion.com/media/documents/3E98EA96/699FFBE9/SE_Flyer_Formaldehyde_EN_web_241016.pdf#:~:text=Page%204,Coming%20soon%20in%20Q2%202026

The leaflet says the sensor is coming in Q2 2026, so even though it is already available, hopefully it will be even more widely available (and cheaper) soon.