How did the ventilation furnace work?

Answer 1

The airshaft ventilation chimney and/or cupolas are rare structures these days, with at least some of those remaining being scheduled ancient monuments. The Nutbrook Colliery furnace ventilation cupola was designed to be remote from the airshaft itself, the furnace therefore being contained at the surface rather than at the base of the shaft. Connection to the airshaft itself would have been via a short inclined tunnel from beneath the base of the cupola. The furnace itself was accessed via an aperture in the side of the cupola, with the airflow (and thus furnace intensity) being controlled here according to the required up-draught. I've no idea whether the fresh air flow was mechanically assisted by the means of bellows, as was the case on similar installations elsewhere.

This method of ventilation was seen as a considerable safety improvement on the underground furnace type, identified by a chimney constructed directly over a shaft. The underground furnace types were implicated in the ignition of mine gases, and could also ignite underground timbers leading to oxygen starvation within workings. At least one of the cupola type furnaces elsewhere operated until the 1950s, whereas by then the Nutbrook structure appears to have acted only as an additional downcast fresh air shaft for the fan ventilated workings of Woodside.