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Count Rumford Fireplaces

Count Rumford cooking fireplace with bake oven

When we were looking for a house in 1976, one of the items on our wish list was a fireplace. We had already learned some fireplace cooking and brick oven baking in a "Crafts at Close Range" program at Old Sturbridge Village Museum and had practiced in an historical society museum.

As it turned out, the house we purchased was built when fireplaces were no longer used for cooking or heating. By then, only well-to-do people might include a fireplace for nostalgic value. The house we bought had three chimneys for wood or coal stoves.

The warmth of a glowing fireplace

From the very beginning, as we restored the home, we had set aside the space in the kitchen for the future fireplace. In 1983, we designed and built a 20' x 26' two story timber frame addition to the back of the house next to the "ell" kitchen. A 9' wide x 4' deep x 7' high foundation was poured for two fireplaces, an oven and two stove flues. The 1st floor, 2nd floor and roof were also framed for the future fireplace structure.

As time went by, I purchased the following books:

The Forgotten Art of Building and Using a Brick Bake Oven by Richard M. Bacon, 1977, Yankee, Inc. The book describes the "technical aspects of brick bake oven construction" as well as its history and use.

The Forgotten Art of Building a Good Fireplace by Vrest Orton, 1974, Yankee Inc. This book was my bible for fireplace design! It tells of an American Tory, Benjamin Thompson, who fled to England during the revolutionary war where he was knighted in 1784. Among his many contributions to science, Count Rumford (an honor granted by the Monarch of the kingdom of Bavaria) wrote a treatise on fireplaces in 1795. He discovered the principal of radiant heat and understood that the heat radiating from the fireplace is what warms the room and everything in it. Count Rumford designed the ideal fireplace to maximize radiant heat.

The large walk-in fireplaces of Europe were soon being "Rumfordized" to have more heat go into the rooms than up the once massive flues. By 1800, Americans were also "Rumfordizing" their inefficient fireplaces by either tearing down to the first floor base and rebuilding them or building the new smaller and more efficient fireplaces inside the older walk-in style brought over from England by the early colonists.

Though far more efficient than the earlier styles, the hay day of the Rumford fireplace was short lived as cast iron stoves with their far higher efficiency began to become common by the 1830's and soon took over for heating and cooking. What happened to the Rumford design? Within a few short years it was forgotten to the extent that when people started building fireplaces later for pure enjoyment, Rumford's principles were not employed and complaints about smoky fireplaces began and have continued to this day.

Here are the basic principals of a Rumford fireplace:

Kitchen fireplace waiting for first fire

-A plum-line dropped from the middle of the fireplace throat will end up exactly in the middle of the floor of the fireplace.

-About 12" above the bottom of the lintel, the smoke shelf should be 4" deep and the flue opening in front should be 4" deep by the width of the fireplace. Ex: My small fireplace is 3' wide, so the opening is 4" deep by 36" wide and the smoke shelf behind is also 4" by 36". The 4" dimensions remain the same for any size fireplace.

-The back wall of the fireplace is equal in width and height to the depth of the floor. Ex: My 3' fireplace is 12" deep so the vertical back wall is 12" wide by 12" high at the point at which it starts to slant front wards towards the smoke shelf opening.

-The front opening should be three times that same depth. Ex: The small fireplace is again 12" deep so the opening is 36". As the front width is 36" and the back wall width is 12", then obviously the side walls must be angled. It is these side angles and the slanted back (above the back wall) which cause the heat to radiate into the room.

- Ideally, the height should be the same as the width. Ex: The front opening is 36"W x 36"H.

Preparing a Thanksgiving meal

 

People think that with such a tall shallow fireplace, the smoke will come into the room. In actuality, it is the faulty design of most modern (post 1880's) fireplace smoke shelves that causes the smoke to enter the room!

The cooking fireplace I built in the dining room is back-to-back to the smaller kitchen one. The dimensions of the front opening are 48"W X 48"H. The back wall should be, therefore, 16" from the front and16" x 16" square. Actually, I chose 20" and 20" x 20" square because the additional depth is necessary for a cooking fireplace and minor changes are allowable in larger fireplaces.

Using the above information, I began drawing out the design for the fireplace structure within the limitations of the space allowed when I built the addition. I used a simple CAD program on my Mac computer. A lot of time was spent on it as I felt it was best that I get it right on the drawing rather than to have to fix mistakes once construction was started.

 

 

Drawings for Count Rumford style fireplace structure

Work on the fireplace structure began in the summer of 1994 when I took out the permit and took down the walls where the fireplace was to be located. Forms for the base were built on top of the foundation which had been poured when the addition was built. The hearth part of the base is cantilevered out from the main base and the total size came to 9'W x 8'D. After mixing and spreading a 3" layer of concrete, I tied together a grid of re-bar for reinforcement and pored the remainder of the concrete.

 
Cooking fireplace half completed
 
Bake oven dome almost finished
& oven floor ready for the bricks
   

Working on top of the dried base, I laid out the shape using strong colored string and began building the structure. I mixed the mortar in small batches in a five gallon pail combining the masonry sand and mortar and using a large drill with a big mixer blade. All the bricks were soaked in a bucket of water first because dry brick would suck the mortar dry. Continuing upward, one full layer of bricks at a time, the fireplaces slowly took shape. When it came time to build the outward slanting back of the fireplaces, templates were constructed and used to get the right slopes.

Reshaping flat stone
which will support oven floor

Dampers would not have been used on the original Rumford fireplaces but are a necessity

now. I was able to use 36" and 48" standard dampers in such a way that Rumford's 4" throat and smoke shelf requirements were not compromised.

Upon reaching the height for the floor of the oven, a large, thin rock was found which fit over the nearly 2' x 3' opening for the floor of the oven. A 2" bed of reinforced concrete was pored over this and a final layer of brick laid flat. The air space under the oven acts as insulation, keeping the heat stored in the oven floor. Solid fill under the oven would have acted like a heat sink removing heat from the oven.

The dome of the oven is made of two layers of brick, laid down in much the same way as an eskimo would build an igloo. Most of the bricks had to be split into trapezoids to form the oval shaped layers which, with each succeeding layer, became smaller and angled so that the smooth side of the brick always faces inwards towards the center of the oven. Otherwise the inside would look like a reverse stairs and would not radiate heat back into the oven well. The overhanging bricks falling in were never a problem as only one layer was done at a time along with each succeeding layer of the whole fireplace structure.

The original oven door with built in damper was found years ago in an antiques store. Lucky for us, as I haven't seen one in good condition for sale since.

Reaching the roof
Flues reach 2nd floor

A coat of mortar is spread over the top of the oven structure once it is complete. Again, to avoid the heat sink effect, I built a brick arch (vaulted) ceiling above the oven. As it is important to have access to inspect and, if necessary, re-coat the oven, a door was built in the kitchen wall and a built-in cabinet placed in front to hide the access door.

Near the end of winter of the second year, I had reached the ceiling of the second floor and had to wait for summer vacation to go through the roof. At that point, the chimney structure was 4' square accommodating one 20" flue for the large cooking fireplace, two 12" flues for the other fireplace and the oven, and two 8" flues for one stove upstairs and another in the basement.

In the spring I designed and built a platform, staging and a crane on the roof. The crane ran on a carriage attached to a 20' was attached. With this, I could lift approximately 200 pound clay flues, brick, sand, mortar, etc. Once clear of the roof, I pulled the carriage along and set the load down on the platform. In this way I was able to build the chimney with a minimum of help. My wife would fill the 5 gal. bucket with bricks and I would pull it up.

 

4 foot square chimney
Scaffolding was erected with overhead sliding
crane to lift and position the materials and flues.

The design for the chimney was chosen from a house in

Freeport Maine which I saw from a second floor window of LL Bean. Once finished, the chimney (as were the two fireplaces) was washed with muriatic acid to clean the efflorescence, etc. which water couldn't completely remove. Then the exterior brick and mortar were sealed with a commercial sealer so that water would not get in and freeze in the winter months.

After two years of part time work and final inspection, we were able to build our first fire!

Eventually, It proved necessary to place a stainless steel cap on top to to keep rainwater from coming down the flues. The cover comes off easily when the chimney is cleaned and the screened sides keep animals out.

We especially enjoy the kitchen fireplace on cool saturday mornings and often keep it going all day. The larger dining room/parlor fireplace is used when we have guests over and when cooking a special meal. Sometimes we bake bread and pots of beans in the brick oven. The small Jotel wood stove in the upstairs den is lit on many winter evenings.

 

Before and after views of the fireplaces:

Ready for plaster, wainscoting and mantel

 

Finished kitchen fireplace

 

Partially finished chimney structure in den

 

Finished den with Jotel stove

 

During construction
Preparing a meal in the cooking fireplace

Enjoying the cooking fireplace and oven:

22 lb turkey roasted in 'tin kitchen' in front of fire
Cooking Spanish Paella over coals
Pots of beans baked in the brick oven over night

 

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