I can find dozens of articles recommending some humidity level, like 60 % at most in winter, 55 % max in summer and so. The recommendations sometimes differ a bit, some say that humidity up to 70 % is OK, some say that it depends on the temperature. They however usually take humidity as it was a single value for whole room or even apartment, which is not always the case. As a result, I am not sure if my care about humidity (ventilation, dehumidifier control) is correct.
Humidity/temperature sensors:
At all the windows – they usually show the highest humidity. Keeping it under 60 % during night without running the dehumidifier seems to be impossible.
At the dehumidifier (even if it is not running) the humidity is much lower, mostly because of higher temperature. The absolute humidity is usually also slightly lower. Note that the dehumidifier is usually at one of the windows.
Bathroom – mostly stable humidity, with some spikes caused by bathing. (But they aren’t so significant when I turn the bathroom fan before bathing)
I plan to measure more, but the sensors haven’t arrived yet.
(I think that fridge and outside measurements aren’t relevant there.)
Objectives:
Elimitation of mold risk – some recommendations are as low as 60 %. I am not sure if mold can just extract the non-condensating humidity (i.e., under 100 %) from air, or if the recommendation is based on the fact that many people don’t measure the humidity at the coldest place, so 60 % at the middle of the room might mean nearly 100 % at the windows.
Health and comfort – I think values at windows aren’t important, just values in places where I am.
I consider adjusting the limits. Not only changing the threshold, but maybe also adjusting the threshold based on time. Before the bedtime, the upper threshold can be temporarily lower, during the bedtime the threshold can be higher. But I am not sure what numbers are OK.
I’ve found http://www.dpcalc.org/ . This allows you to compute various risks (mold, corrosion, …) for selected humidity and temperature. (Or you can use dew point instead of one of those variables.) I’ve primarily looked for range 10°C – 40°C, which is probably wider than neccessary.
Mold risk: It seems that DPCalc mostly follows max_acceptable_humidity_percentage = max(88.0 - temperature_celsius, 65.0). Sometimes, DPCalc is slightly more permissive (by 1 percentage point) than the formula. So the formula is slightly more on the safe side.
Corrosion risk: By DPCalc, I the maximum acceptable humidity varies from 56 % to 61 %. I don’t care that much. Metals are usually painted or stainless.
Other risks mentioned by DPCalc: I don’t understand them well, but some of them are rapidly restrictive when you are over 18°C. When you are over 22°C (which is often my case even with heating off), you would have the humidity under 40 %, which is probably not desirable. My furniture is probably not that expensive to justify both potential health issues and energy for dehumidification.
Health (various sources, not mentioned by DPCalc): I don’t understand it well, but it seems that I have to keep it under 60 % (or 55 % in summer) and over 40 %.
So, it seems that there are two/three strategies to use on various places:
Health – this gives me more narrow range for the humidity. It makes sense in places inside (not near the windows). In reasonable temperature range, healthy humidity seems to imply eliminating the mold risk.
Mold risk (+ some safety margin) – this gives me a wider range suitable for window parapets. The temperature there is usually lower, so the relative humidity is usually higher. Health risks from humidity over 60 % (whatever they are) aren’t much relevant there, as I usually don’t put my face at window parapet to breathe this air. So, taking care just about the mold risk seems to be enough.
Bathroom – I’d care about healthy air + mold risk in bath. However, with just one sensor, I might end up with more strict strategy. Or with adding a second sensor. Or moving the existing sensor.
(EDIT) Clother dryer – potentially a different strategy, maybe based on comparison to some other sensor. (Yes, I know, I am off-by-one.)
A few years ago, after moving to a colder city, I started getting sore throat quite often and the doctors couldn’t find anything (no inflammation). Then by a coincidence I installed a Tado TRV which humidity measurement and realized the humidity at my home was low and the app was saying that could be bad for my health, then looking for that I found somewhere about right levels, found lots of different information but, in the end (and I don’t remember exactly how I got to this) I’ve set a couple of humidifiers to keep the relative humidity with the target of 40% ±3%, controlled by Home Assistant, and the sore throat has gone since then…
As you came with this topic now, I will follow the discussions here and try to find more info in order the find for better set points for health and confort…
