Saltfire ST-X8 DEFRA Approved Wood Burning Stove. TheSaltfire ST-X8 is an DEFRA Approved Multifuel Stove. TheST-X8 is the largest stove of the ST-X range. Defra ApprovedYes. Ultra-Clean Burning. TheST-X8 has a particularlylarge firebox for an 8kW model allowing a greater range of heat output and forlarger logs to be burned.