Building a Hot Blast Stove — Preheating the Air That Tripled the Blast Furnace

For centuries ironmasters believed a blast furnace ran best on cold winter air, and blew their furnaces with air at whatever temperature the weather gave. In 1828 the Scottish engineer James Neilson proved the opposite: heating the blast before it entered the furnace slashed the fuel needed and raised the output enormously. The hot blast was one of the great efficiency leaps of the iron age.

The idea seems backwards but the physics is sound. Cold air entering the furnace has to be heated by burning precious fuel before it can do its work; preheating the air outside the furnace, using waste heat that would otherwise escape up the chimney, means far less coke is wasted just warming the blast. Neilson's first stoves cut coke use by a third, and later regenerative stoves did far better still.

A hot blast stove is a chamber of brick or pipe that the blast passes through on its way to the tuyeres, heated by the furnace's own escaping gases. Bolted onto the pig-iron blast furnace, it made iron dramatically cheaper — and cheap iron was the lifeblood of the Industrial Revolution.