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When I got my piano, I promised my family I wouldn't go crazy with it. So of course I immediately went out and started getting all kinds of accessories (like the coffee table for my morning brew).

I just got a tiny bluetooth thermometer/hygrometer to track the humidity, and I just set it atop one the beams/backposts right under the soundboard. I'm kind of blown away that these things are less than $15. What's more, Home Assistant just updated with an integration for it, so now I can see, track and utilize it in my little home automation setup. Alerts when temp/humidity go out of range, automated start/stop for connected fan/AC/dehumidifiers, etc. Pretty interesting possibilities here.

[Linked Image]

But for now, I'm just running it for a few days to calibrate against my standalone thermometer. This 60%RH reading isn't looking good eek


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I was surprised at the variation of RH in various locations around the room. I also hung a sensor right under the soundboard and compared that to the reading at the center of the room, on the floor and on the ceiling and in the corners. The temp difference between floor and ceiling explains some of the variation but I often had readings that varied 5%RH in different locations. It would be interesting to know if you observe the same thing.


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Interesting gadget. It would be interesting to know the precise name of it?

Humidity measurement is notoriously inexact. Do you have any idea how accurate this is?

Impressed that you can record temperatures to the nearest 1/10,000 of a degree!

I wouldn't necessarily worry about the 60%. More important is how stable this is. Can you chart the readings somehow?

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Originally Posted by MarkL
I was surprised at the variation of RH in various locations around the room. I also hung a sensor right under the soundboard and compared that to the reading at the center of the room, on the floor and on the ceiling and in the corners. The temp difference between floor and ceiling explains some of the variation but I often had readings that varied 5%RH in different locations. It would be interesting to know if you observe the same thing.


I read that these cheap RH meters aren't particularly accurate. The specs say +/- 3%, but I also didn't bother going through an initial calibration (what would I calibrate to? Do I have to pull a glass full of salt water in a ziplock bag or something?), and just turned it on.

I have a standalone RH meter under the top of the lid, which reads 47%. The logged bluetooth one reads 53.2% right now. I'll probably put them side by side for a while and see if they get close.

I'm not too concerned about absolute accuracy; so long as it's close and good enough to track up/down trends.


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David-G, missed your response earlier!

The model is the Govee H5174 (H5174001) on Amazon.

It claims +/- 3% accuracy, and also allows for manual calibration.

I got a kick out of the temp precision too laugh

It provides a 20-day chart in-device, will download the log to your phone, and Home Assistant can separately keep a perpetual log, which is mostly why I got it (so I can see hour to hour swings):
[Linked Image]


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@Gombessa - you're giving obssesive a bad name :-)

FWIW - the RH, when I was visiting Waldkirch, in Bavaria at this time of year, was routinely about 53%. I imagine the Vienna conditions would have been similar. My own piano studio here in the USA, in which I've installed a MiniSplit HVAC system sits right around 60% in the summer and 40% in the winter. I keep the temperature set at 74F all the time. Right now, the pianos (Bechstein K8 and the Steinert Artist Grand) are sitting about 7 cents sharp of A440. Come the winter and the humidity drop, they will go 10 to 12 cents in the other direction (that is 3 to 4 cents flat). Then they remain stable through the seasons. Last complete tuning of the Steinert was nearly a year ago. The Bechstein was tuned in May, and I suspect next time I tune it will be late October, early November. I have damp chaser systems on both instruments, and for me, they have made a difference. I tried disconnecting the one in the Bechstein, and it kept going sharp, day after day, as the board absorbed that extra humidity in the atmosphere. Once I plugged in the DC, that stopped, again, literally over night, and since then, it's stable. The 1929 Steinert is less subject to the up and down swings; I don't know why. Board is original.

Grist for your mill.

Last edited by Seeker; 08/05/22 07:07 PM. Reason: Clarification

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Well thanks alot. Now I have to get a hygrometer with app . Seriously have been putting it off but should probably take good care of this piano as I doubt I'll be able to afford another.


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Exact humidity value (in a reasonable range, of course) is not as important as its stability.
Even if the hygrometer is not very precise as long as it shows the same humidity you should be good.


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Originally Posted by Gombessa
...(what would I calibrate to? Do I have to pull a glass full of salt water in a ziplock bag or something?)
There are different salts that saturate at different RH. The one to use for piano is potassium carbonate, it saturates at 43%. The sensor I have is attached to a controller that allows an offset to be added, so the device always reads correctly and you don't have to add or subtract in your head.


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Here are hygrometer test results that I did a while ago where you can see which salts can be used for calibration at difderent RH. Some of these salts can be hard to buy depending on your location:

[Linked Image]


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Thank you VladK, super helpful. I don't have any potassium carbonate salts lying around, so I thought I'd give table salt a try. It's only been about an hour, but so far my BT hygrometer is hovering around 73-74%, and my other portable hygrometer went up to 75 and is now down to....50%?

Also, here's a bit of a funny discovery. I found a spot under the belly to temporary stick my portable hygrometers as a control/calibration for the BT unit (which doesn't have a screen, so I can put it anywhere):

[Linked Image]

However, it wasn't until this morning when I crawled under to fetch the BT and one of the other portable units for the salt calibration, that I noticed that I was not the first to discover this little hiding spot under the piano!

[Linked Image]


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Originally Posted by VladK
Here are hygrometer test results that I did a while ago where you can see which salts can be used for calibration at difderent RH. Some of these salts can be hard to buy depending on your location:

[Linked Image]

Good info.

The thing is these digital hygrometers are pretty accurate but they are *not* particularly linear. What that means is that you should calibrate your hygrometer using one of the above salts whose humidity is closest to the humidity you intend to keep your piano at. For most of us that means Potassium carbonate as it is in about the right range, is readily available and pretty safe to use. Be aware that, because these instruments do not have laboratory grade linearity, if you calibrate them with salts way away from your target humidity they are likely to be *less* accurate at normal ranges than they come out of the box where the manufacturer has calibrated them with (probably) Potassium Carbonate.

FWIW the govee mentioned earlier is pretty good. Mine was accurate out of the box to within 1.5% at 43% calibration which is certainly good enough for our purposes and, to be frank, as accurate as I can reliably calibrate in anyway. Other devices I measured were all also pretty good and would have been usable without messing about - the worst one was 5% out but it really was a cheap piece of junk, generally they were OK within 2% or so.

As mentioned earlier I also find RH in different parts of the room, especially at different heights, varies quite a bit. It also changes (or at least the hygrometers give a different reading :-) ) if there is air movement or if you are moving the hygrometer.

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Originally Posted by VladK
Here are hygrometer test results that I did a while ago where you can see which salts can be used for calibration at difderent RH. ...
Great data, thanks for posting


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Originally Posted by Gombessa
However, it wasn't until this morning when I crawled under to fetch the BT and one of the other portable units for the salt calibration, that I noticed that I was not the first to discover this little hiding spot under the piano!

That's where I keep my stuffed animals too.


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There are few notes to keep in mind if you want to do a salt test:
1. I put the salt solution and hygrometers into sealed ziplock bag nested in another ziplock bag to create isolated air tight area. Salt solution is in glass pot, and hygrometers are nearby without direct contact to the pot. The bigger the open surface of the pot the better - salt solution should interact with air.
2. The salt solution should be made from salt and distilled water mix as a gel (all the water should be absorbed by salt, and no salt crystals that do not have some water absorbed). The salt solution should be able to absorb moisture from air and to release moisture to the air to stabilize conditions. In my tests 1-2 tablespoons of salt was enough. You carefully agitate salt solution if you see the surface shows free water or dried salt, but do this without opening ziplock. I kept a glass wand in the pot during the test.

Last edited by VladK; 08/06/22 02:34 PM.

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Originally Posted by VladK
There are few notes to keep in mind if you want to do a salt test:
1. I put the salt solution and hygrometers into sealed ziplock bag nested in another ziplock bag to create isolated air tight area. Salt solution is in glass pot, and hygrometers are nearby without direct contact to the pot. The bigger the open surface of the pot the better - salt solution should interact with air.
2. The salt solution should be made from salt and distilled water mix as a gel (all the water should be absorbed by salt, and no salt crystals that do not have some water absorbed). The salt solution should be able to absorb moisture from air and to release moisture to the air to stabilize conditions. In my tests 1-2 tablespoons of salt was enough. You carefully agitate salt solution if you see the surface shows free water or dried salt, but do this without opening ziplock. I kept a glass wand in the pot during the test.

Yes, thanks.

If I was working in a lab environment I think I could produce pretty consistent results but at home I struggle and it is harder than it sounds. The mechanics of stirring salt solutions inside ziplock bags without spilling anything and maintaining suitable and reasonably constant separation between the solution and hygrometer and the bag itself isn't exactly easy - doubly so if the hygrometer you want most to calibrate accurately is a mains powered controller so you use up most of the ziplock bag space sealing it around the cables.

Still, it can be done sufficiently accurately for our purposes I think. But it is a fiddle and I did get some differences between test results as great as the accuracy of the better units so I do come back to my original viewpoint that it seems most of the calibratable digital hygrometers seem to be good enough 'out of the box' for our purposes and you aren't necessarily going to improve them with calibration. Not unless you use a suitable salt, do the calibration carefully, and do several calibrations so that you can throw out outliers and average them. Even then what doyou gain if your hygrometer reads to within 1% rather than 2%?

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You can purchase calibration kits made for different humidity settings. Takes a lot of the home chemistry lab challenges out of the process.


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So I tried a calibration over the weekend, using what I had (table salt, tap water):

1. All my hygrometers, are portable/wireless, so it was easy to put everything in a zip lock bag.

2. A soda bottle cap isn't enough salt. The humidity spiked to 75% but then quickly dropped to 65%. So I used a ramekin with 2TBS salt, which worked.

3. I put 3 hygrometers in the ziplock bag. Turns out that the new Govee bluetooth one I got, which reads the highest out of all three, is the most accurate, pegging at 76.1% in the bag (which the others were 71% and 69%). 76% is close enough to 75.x% that I didn't bother changing the software calibration.

4. This morning (and normally), there's a huge discrepancy between all the hygrometers, even sitting right next to each other. BT Govee reads 58.2%, Hygrometer 2 reads 52%, Hygrometer 3 reads 50%. Since the 58.2 was the most accurate in the salt bag, I'm just going to with that.

I'll pick up a room dehumidifier and see if that makes a difference.


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Originally Posted by Seeker
@Gombessa - you're giving obssesive a bad name :-)

So Seeker, you may want to sit down. No, no on second thought, you'd better strap yourself in. smile

It turns out I have 5 hygrometers. 4 tend to agree, but the one I really care about, the connected bluetooth Govee, reads 5-8% higher all the time. And when I stuck it in a salt bag, it resolved to 75% which sounds right, so I didn't want to just offset it in software. So I got 2 more.

Now I have 7 hygrometers.

My original Govee definitely reads the highest out of everything. The two newer ones are consistently lower than it, but only by 1-2%. So that suggests to me the original is more or less in spec. I probably should have let it be. Right now, I'm seeing readings of 40, 41, 42, 43, 45.7, 46.8, and 47.7 (the Govees have decimals).

[Linked Image]

I'm trying out a whole room dehumidifier. I'm pretty sure I won't be able to tolerate it...but will give it a fair shake at a few days. Even with low fan speed, it's quite loud, it warms the whole room all the time (and this is summer!), it fills up its tank at least once a day, and I think it takes 600-800w of power as it runs....24/7. Wow.

But it works amazingly well. Normally, during the course of the day the humidity spikes to 63% on the Govee (55% on everything else). With the dehumidifier on, within an hour the RH dropped to 55, then 45 (40 according to everything else), and just stays there. Here's 4 days' RH output, the red arrow below is when I turned the dehumidifier on for the first time:

[Linked Image]

But at what cost?? Look at that temperature spike during the same time.


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Originally Posted by Gombessa
But at what cost?? Look at that temperature spike during the same time.

What type of in-room dehumidifier do you have? A dessicant dehumidifier is going to be more efficient in cold condition and will give some welcome heating as well. Above about 27 degrees centigrade or so the condenser/compressor based models become more efficient and shouldn't have much effect on room temperature - as an example mine only runs at 250w max and is usually doing nothing at all and is helpfully quieter as well. The dessicant model I use in winter does run up to 600w but I need that as, in an unheated room in winter, the compressor model is spending most of its time/energy in defrosting the condensor coil.

The best type is going to depend on your climate and temperature levels - but from your comments I'd suspect a compressor model might be best for you.

P.S. I'll repeat my old offer in this thread here as well (for any new readers living in the UK), send me an SAE I'll give you some Potassium carbonate from my spare stock.

Last edited by gwing; 08/11/22 09:18 AM.
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