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I have a cheap hygrometer thermometer.
Also an automatic humidifier with built in hygrometer and thermometer.
The humidifier is on the floor and the hygrometer is on the piano.
The temperatures are within a degree or so of each other. Understandable being at different levels.
But the relative humidity readings are about 15% different.
What hygrometer would you recommend to get a more accurate reading?

Is the heating on? If yes here is a way that you can estimate the current indoors humidity.

Outside temperature is 7C (45F) & 55% humidity.
Inside is about 17C (63F).
That means my rooms humidity cannot be more than about 40% RH without using a humidifier.
My hygrometer is reading about 50%.
The humidifier is targeting 65% with a low setting, so it spreads the humidity more evenly through the house.

With those numbers I find it from the chart as 30% not 40%.

Thank you.
Looking again, you are correct. 30% looks more accurate.
So having my humidifier on is correct?
And the 50% reading of the hygrometer is probably more accurate than the 65% of the humidifier?
(The readings fluctuate a bit, 48-52%, 60-65% respectively).
Nothing feels damp and no condensation on windows.

You can use the below values for maximum indoors humidity for the respective outside humidity values, so that there won't be condensation etc.


For 63F indoors temperature you might be safer.

Sorry for the typo, it should be for the respective "outside temperature" values.

Fenner, the air has been particularly dry in the UK these last two weeks. If you have the heating on, I wouldn't be surprised if 30% indoors is correct. These frosty nights are precisely the time of maximum danger, when use of a humidifier is most important.

You should test your hygrometer with a bottle cap of slightly damped potassium carbonate in a sealed bag and calibrate it accordingly.

Until then your room could be at 50% or 65% or some other value depending on how much water the humidifier is putting into the room.

I don’t think I can calibrate my hygrometer. It’s a cheap one.
What one would you recommend that can be calibrated?
AcuRite and Caliber are 2 makes that get recommended by reviewers.

You do not necessarily need to calibrate. You just need to know the offset at few measurement points.

This one claims to have +/-2% RH accuracy with manual calibration option.

https://www.acurite.com/shop-all/we...or-temperature-and-humidity-monitor.html

Unfortunately, the web site just says:

"AcuRite.com is currently unavailable in most European countries. We are engaged with the issue and committed to looking at options that support our full range of digital offerings to the EU market. We continue to identify technical compliance solutions that will provide all users with our time, temperature, and weather solutions."

This is despite the UK not being in the EU market!

Hakki, could you tell us if there is a model number for this? Then I could try it on Amazon.

I can thoroughly recommend the Govee room thermometer/hygrometer which was accurate to 2% RH (within the range we are interested in) out of the box and is a data logger which pairs with a phone app as well. Having a conventional hygrometer is of relatively limited use because you don't look at it very often but you get pretty graphs showing how RH varies with time and seasons if you have this.

Alternatively if you don't want a logging facility it is worth considering the Inkbird humidity controller. That has an accurate hygrometer and high/low power outputs so you can connect it to humidifiers and stuff for a DIY damp chaser or whole room equivalent.


Both of those are available on Amazon.

P.S. It isn't really necessary to calibrate either of these as they are accurate enough out of the box (it is after all swings in RH we are really interested in not the absolute value). But if you do set it use Potassium Carbonate to calibrate at 43%, if you calibrate with normal Salt at 80% the non-linearity of the instruments means that at the 40->50% we are really interested in the device will be *less* accurate than as originally supplied. That was the case for the three instruments I tested anyway. Also of note is that the hygrometer on the Meaco dehumidifier I have is surprisingly accurate and there is also a surprising difference between the RH at floor level and that on top of the piano. I can give you some Potassium Carbonate if you just want a small quantity for calibration.

The model number is 01083. It appears on Amazon.

Actually we are interested in the correct Rh as well other than the swings.

So it is required to calibrate the hygrometer with the potassium carbonate method.

I do admit to being interested but the of the four digital hygrometers I checked two were within 2%, one within 3% and one (a really cheap one) within 4% so all were more than accurate enough already for piano keeping purposes. Admittedly they were all a lot loss accurate at 80% RH but that isn't of much concern.

I currently have a ThermoPro TP49

Might be worth investing in a wet and dry bulb hygrometer as they do not appear to be expensive.

Send me an SAE and you can have some Potassium Carbonate to check it. Then even if it cannot be calibrated you can allow for its innacuracy. Or just buy this
Logging Hygrometer

Note this isn't the actual model I own and have tested, but it is less than half the price of the WiFi version and (probably) does the same job.