In 1885, when you could still buy a milk cow for $29.70, Albert Butz, a Swiss immigrant living in St. Paul, Minnesota, invented what he called the damper-flapper. He patented it the following year. The flapper opened a damper that allowed outside air to enter a coal-fired home furnace. This increased the oxygen in the furnace and made the fire burn hotter. When the temperature rose to a desired point, the damper closed.
