The efficiency of the blast furnace was improved by the change to hot blast, patented by James Beaumont Neilson in Scotland in 1828.  This further reduced production costs.  Within a few decades, the practice was to have a stove as large as the furnace next to it into which the waste gas (containing CO) from the furnace was directed and burnt.  The resultant heat was used to preheat the air blown into the furnace.