A Modern Heating System

by Ellen Nielsen

(from The Unity Newsletter, July 2002)

When the Chase Tavern was built 200 years ago, it incorporated an elaborate heating system, based on the most recent design innovations.  The system survived, with some damage, and after being repaired, will be on display in the restored building.  It consists of eight Rumford fireplaces, built into two massive chimneys supported by brick barrel vaults in the basement.

The first account of Rumford fireplaces was published by Sir Benjamin Thompson (later Count von Rumford) in 1795.  But Benjamin Thompson was not an English aristocrat by birth; he was born in Woburn in the colony of Massachusetts in 1753.   In 1772 he married a wealthy widow, Sarah Walker, and lived in Rumford, N.H.  (The name was later changed to Concord, and the town became our State capital.)   Although he joined the New Hampshire militia in 1774, Benjamin Thompson was a Tory sympathizer, and served as a spy for the British Army unit commanded by General Gage. 

After the fall of Boston to the Revolutionary forces in 1776, Thompson fled to England.  Later he returned to serve as an officer in the British Army, but left the former colonies for good after the end of the war.  He was knighted by King George III and lived first in England and then in Bavaria, where he had a successful career in government service and was created Count von Rumford of the Holy Roman Empire in 1791. 

Thompson is now remembered, not for his political career with its twists and turns, but for his inventions and scientific achievements, most notably for his theory that heat is a form of motion.   His practical accomplishments included the invention of the double boiler, the drip coffeepot, and an early form of a kitchen range, as well as the introduction of the potato as a staple food.  He was an early promoter of James Watt’s steam engine.  And, along with other innovative thinkers such as Benjamin Franklin, he worked on the problem of heating interior spaces more efficiently while producing less smoke.

Franklin’s efforts led to the Franklin stove; Thompson’s led to the Rumford fireplace, a design which is still used, which combines a shallow firebox which radiates heat into the room, with exact proportions between the sizes of the firebox and the throat of the chimney in order to minimize smoke. 

According to historic preservation specialist Jim Kahn, Chase’s Tavern contains very early examples of these fireplaces.  The largest of the fireplaces is in the former kitchen, which will become the Town Clerk’s office, and has built-in ovens beside the firebox.  There are three medium-sized fireplaces in other first floor rooms, and four smaller fireplaces on the second floor. 

Down in the basement, two immense thick-walled brick barrel vaults support the weight of the fireplaces and the two brick chimneys.  The smaller vault is 4’8” wide by 8’ long and the larger vault, under the kitchen, is 7’ wide by 10’ long.  Now that the space underneath them has been cleaned out, it’s possible to stand inside them.  The walls of the vaults were laid up to the point where the arch starts to curve inward.  At this stage the original mason left notches in the brickwork to hold timber crosspieces, which supported wooden forms.  The brick arches were then built over the forms. Upstairs, half-arches were built, using the same construction technique, a method known to the ancient Romans, to support the hearths. 

The brickwork of the vaults, chimneys, and fireplaces was damaged by frost heaving during the winters the Tavern sat unheated, but the damage is being repaired.  Repairs to the barrel vaults are complete and it’s easy to see the difference between the modern gray mortar, made with cement, and the grainy cream-colored original mortar, made with lime.

Later in the nineteenth century, wood or coal stoves were installed in front of the fireplaces; the holes in the chimneys where the thimbles for the stovepipes were inserted are still visible, filled with cement mortar.   For safety reasons, the restored open fireplaces will not be used to heat the Tavern.  Instead, a modern oil furnace is being installed.  But this carries on the tradition—when they were built, the Rumford fireplaces were the latest thing!

Meanwhile, the addition to the building has been framed and will soon have a roof.  Plumbing and electrical work in the main building are well underway and a septic tank and leach field have been installed.  The new windows have just been delivered.  The fireproof vault for the Town records has been completed.

[Information for this article came from an interview with Jim Kahn and from the Encyclopedia Britannica.]

Pictures by Doug Lawson and Jim Romer