Former Lewis Merthyr Colliery fan house

The former Lewis Merthyr Colliery fan house is a single-storey rectangular gabled structure built of sandstone rubble and rockfaced stone, with brick and stone evasees and ducts to the north, and a Welsh slate roof. The building has seven bays on the sides and one bay on the gable ends. The south elevation features sandstone rubble with rockfaced dressings, which includes four round-headed windows with 26 panes, each having voussoirs, a keystone, and a sill, along with three similarly shaped doorways, the central one flanked by pilasters. The east elevation, made of snecked rockfaced sandstone, has a single blind round-headed arch with voussoirs, a keystone, and a sill between pilasters, topped with an oculus. The north side has blocked windows and blocked yellow brick basement arches. A louvred ventilator is present on the roof.

To the west, the building is extended by a gabled corrugated metal roof that connects to the Trefor pitbank. The fan chamber to the north is a flat-roofed structure made of yellow brick and stone, extending at eaves height and connected from the west by a sloping duct made of rubble sandstone with a corrugated metal covering. A square red brick evasee is attached to the northeast corner of the fan chamber.

Inside, the roof is open and supported by corbels on the side pilasters, with brick dressings around the windows. The area that would have housed the fan engine has been converted into a classroom, but the 14-foot (4.28 meters) diameter Schiele iron fan from 1891 remains in place. Its shaft features a pulley wheel with grooves for ten cotton belts, which were used to transmit power from the engine. The bearing of the shaft can be seen on the north exterior of the building in a recess under a timber lintel. The interior of the fan drift is made of yellow brick with round-headed arches, some of which have deep brick intrados, and includes an access passage.