The problem of eggs that do not hatch, despite being fertilized, encountered by breeders gave me the idea of this topic.
The importance of the humidity level during egg development and hatching in our rearing rooms pushes us to find solutions to regulate it, especially during dry periods.
I use an ultrasonic humidifier, adjustable and ideal:
I also use, either in parallel with the humidifier or when there is only a need for a small adjustment of the humidity level, a much less expensive solution: Ceramic saturators (around 5 euros per unit in DIY stores) :
I hang them on the oil bath radiator (which dries the air less than electric radiators of the radiant type or commonly called "Toaster").
The principle of evaporation caused by heat from the radiator works well, however it takes about a day to see the effects.