Heating is effected by means of hot-water pipes below the beds, and against the side ventilators.
the closing of ventilators (accompanied by syringing and damping of surfaces to produce a humid atmosphere) has for its object the conservation of as much solar heat as practicable.
In large roofs, ventilation can be improved with ridge ventilators.
About 1850, efficient ventilators of the centrifugal type were first introduced, and are now almost universally employed where the circulation of large volumes of air is necessary, as in collieries.
The use of small auxiliary blowing ventilators underground, for carrying air into workings away from the main circuits, which was largely advocated at one time, has lost its popularity, but a useful substitute has been found in the induced draught produced by jets of compressed air or high-pressure water blowing into ejectors.