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There have been a number of threads pointing out that you cannot trust a relative humidity gage unless you calibrate it periodically with a wet bulb hygrometer, which is quite easy to do. The same would go for most, if not all, humidifiers or dehumidifiers that represent a scale on a dial. So, the search will probabaly not be for a machine that has relative humidity printed on a control dial, which would be in error and need calibration. You need to find a reliable machine at a decent cost. You then test the relative humidity with a wet bulb hygrometer after you set the machine and give it a day to equilabrate. Adjust as needed, until it appears stable. The machine will change efficiency with temperature and other factors, so you need to recheck with the wet bulb periodically, even if you think things are stable. You should also have a small electric fan running continuosly.

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I use a mid-range domestic Hinari Dehumidifier that can draw up to 40 litres a day- On the full setting it can bring a room down to acceptable RH in one hour. Because up in the Midlands, the RH is pretty constant, I have the dehumidifier on a timer switch for certain times of the day.

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