So far, we’ve talked about spies and condensed milk, Vaseline and the Civil War. This month, we’ll go further back in the country’s history, fudge the date a bit, and talk about one of our most famous citizens. On June 14, 1742, Benjamin Franklin invented his Franklin stove.
Up until then, houses were heated with fireplaces. This was an inefficient method, as much of the heat simply escaped up the chimney. Franklin’s cast iron “Pennsylvania Fire Place” was a metal-lined fireplace that had rear baffles for improved air flow and provided greatly improved heating with less smoke and less wood used. The stove heated the entire room evenly and the metal walls absorbed and radiated heat even after the fire went out.
Baffles in fireplaces weren’t a new idea, but Franklin’s stove baffles performed two functions at once. The idea behind a baffle is to lengthen the amount of time the air spends in contact with the stove, thus transferring more heat to cooler air and from the smoke. The Franklin stove’s baffle was positioned inside and to the rear of the stove. It was a wide but thin cast iron box which was open to the room’s air at the bottom and at two holes on the sides near its top. Air entered the bottom of the box and was heated by both the fire and the fumes flowing over the front and back of the box. This warmed air then rose inside the box and exited through the holes in the baffle’s sides. This pathway both lengthened the pathway the fire’s fumes followed before it reached the chimney, allowing more heat to be extracted from the fumes, and placed a duct near the fire, which heated the air by convection.
Franklin’s stove also made use of what he called an “aerial siphon” or “siphon revers’d.” This was a U-shaped duct connecting the stove to the chimney which drew the fire’s smoke and fumes first downward through one leg of the U, then upwards through the second leg and the chimney. This functioned to extract even more heat from the fumes before they exited via the chimney. In order for this design to work, the U-shaped duct was installed beneath the home’s floorboards before connecting to the fireplace chimney.
In Franklin’s own words: “In Order of Time I should have mentioned before, that having in 1742 invented an open Stove, for the better warming of Rooms and at the same time saving Fuel, as the fresh Air admitted was warmed in Entring, I made a Present of the Model to Mr. Robert Grace, one of my early Friends, who having an Iron Furnace, found the Casting of th Plats for these Stoves a profitable Thing, as they were growing in Demand. To promote that Demand I wrote and published a Pamphlet Intitled, An Account of the New-Invented Pennsylvania fire places: Wherein their Construction and manner of Operation is particularly explained; their Advantages above every other Method of warming Rooms demonstrated; and all Objections that have been raised against the Use of them answered and obviated. &c. This Pamphlet had a good Effect, Govr Thomas was so pleas’d with the Construction of this Stove, as describ’d in it that he offer’d to give me a Patent for the sole Vending of them for a Term of Years; but I declin’d it from a Principle which has ever weigh’d with me on such Occasions, vis. That as we enjoy great Advantages from the Inventions of others, we should be glad of an Opportunity to serve others by any Invention of ours, and this w should do freely and generously.”
Benjamin Franklin was a true genius who invented and created many of the things we still use today. He was only 36 when he invented his fireplace, and was inspired by two other inventors: Franz Kessler, who invented the inverted siphon, and Jean Desaguilliers, who utilized metal in his fireplaces. Benjamin’s design was improved upon by others, including David R. Rittenhouse, who added an L-shaped chimney in the late 1780s. He called his appliance the Rittenhouse Stove—but the public continued to call it a Franklin Stove. Your characters, if they have one in their home, would call it the same.