St Paul's original warm air convection heating system was designed by Hadens of Trowbridge and is understood to be one of the only twenty known still to exist. Four double grates in the nave allowed the warm air to circulate.
Twin portico-topped fires were stoked with coke (some fuel remains in 2009). The tall doors allowed access to clean out the smokeways before the flue gases reach the chimney.
The Hadens were known to be a religious, non-conformist family; it is understood that the architect, Gilbert Scott, and George Nelson Haden were friendly and Scott often gave Haden the commission to design and install new Church heating systems (John Ferris, Hevac Heritage)
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