Holding 45–55% RH in a print hall
19 August 2026Application4 min read
Paper changes dimension with humidity. In a press hall the working band is narrow, and both drying and humidifying may be needed in the same week.
Paper and board take up moisture from the air and expand or contract as a result. Registration errors, curling and static are the visible signs; the cause is a relative humidity that moves outside the working band.
A band of 45–55% RH is the usual target for offset and digital press halls. Holding it means controlling both directions: drying in wet weather, humidifying in winter or under heavy air-conditioning.
Where the moisture comes from
In a press hall the load changes through the day. Ink and fountain solution add moisture, drying equipment removes it, and outdoor air brought in for ventilation shifts the balance again.
- Measure at the press, not only at the wall: the paper stack and the feeding area see different conditions.
- Keep the band narrow enough that paper is conditioned before it reaches the press.
- Plan storage and press hall as one zone, or accept a settling time between them.
Equipment combination
A condensing dehumidifier covers the upper end of the band. For winter operation an ultrasonic or wet-film humidifier adds moisture without wetting surfaces. Both are usually controlled from one humidity sensor so the hall does not fight itself.