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Rumford Fireplace: Lord of the Flues

Rumford Fireplace: Lord of the Flues
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When it came time to build a fireplace, Roger Wells told his mason that he wanted a Rumford — the single best fireplace design to come along in the last 200-plus years. Count Rumford, born Benjamin Thompson in 1753 in Woburn, Massachusetts, was a physicist and genius inventor, a Tory who fled Boston with British troops in 1776 (after he was accused of informing on the Minutemen).

In London, Thompson experimented with gunpowder and other explosives, developed new methods of signaling at sea, and published a treatise on how to build a fireplace that would heat but never smoke. King George III was so impressed with Thompson that he knighted him. Later, Sir Benjamin spent 11 years in Bavaria in various posts, including minister of war, and for this service was made a count of the Holy Roman Empire in 1791. Thompson took the name “Rumford” from his wife’s birthplace, now Concord, New Hampshire. The Rumford remains one of the most efficient fireplaces you can build.

Read Tim Clark’s review of a new biography of Count Rumford.

Detail, from Robert Kaldenbach

The well-tempered Rumford fireplace features a throat that is a bare four inches from front to back, running the full width of the chimney, all the better to keep heat down below and create a strong draft above. At the throat, where the fireplace becomes the chimney, a shelf (X-Z) has been built so that rising smoke meets and mixes with fresh air entering the chimney from above. A Rumford fireplace locates the fire toward the front, directly beneath the chimney, so smoke rises vertically to the throat without turbulence. Rumford narrowed the fireback, which allowed the sidewalls to be slanted. The fireback width (A-B) is the same as the fireplace depth(B-C), creating a square floor.

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5 Responses to Rumford Fireplace: Lord of the Flues

  1. Kevin Coughlin January 13, 2009 at 6:47 am #

    I believe the diagram published with this article is depicting a variation of a Rumford fireplace but not a true Rumford. The true Rumford has a plumb (straight) fireback and rounded streamlined throat. Please visit the Rumford.com website where you will find details about Rumford and the actual papers written by him complete with his original drawings. Jim Buckley does a fantastic job of covering all of the aspects of this fireplace design.

    http://www.rumford.com/

  2. Francis Casini March 15, 2010 at 12:47 pm #

    I have been building successful slanted back rumfords since I was handed a book written by Vrest Orton back in 1970.

    Rumford mentioned in a footnote that out of 600 fireplaces he altered, the single best heater was the slanted version which he was forced into building on a bedroom fireplace because his hearth layout was 12” to 13” deep and the back wall in rising plumb up to the top of the back of the throat which was most always 4″[and sometimes 3″ on the better drafting chimneys] and placed just behind the front wall.
    Normally he encountered thick front walls in those huge castle like homes so it worked out, and if the front wall was too thick to cause a greater than 13” depth for his smaller boxes,he’d simply have a recessed jamb so as so to indent the face adjacent to the firebox. But in this particular bedroom fireplace he would only have a depth of 8” [the front wall and the 4” throat, then plumb down to the hearth floor] and it wasn’t big enough.So he slide the fire back wall 4 to 5 inches back and came up plumb to 10” above the floor and gently leaned the back to the bottom back side of the 4” deep throat. He went on and experimented and was to release his results but never did and this is perhaps the catalyst to prompt certain people to make comments such as “not a true Rumford” and “prone to smoke”.
    Orton did note that Ben Franklin was publishing his writings on his stove around the same period and this probably side tracked Rumford, especially if he factored in the extra labor and cost that one would have incurred when incorporating the slanted version in those thick walled castles,for the mason would have to remove much of that front wall to [in some cases]up past the second floor as to gently lean the chimney back.

    There are certain do’s and do-not’s when deciding on a slant back and as in all fireplaces the ideal place is in the interior of a home, but if a slant back should be placed on the exterior, I always have the framer leave the opening at the box height 8′, to allow for an easy slope backward of the smoke chamber / flue, and let the plywood hang down till I build the exterior then I cut and frame to what I need,depending on if the chimney narrows,and where, or it just stays the same on up.
    Here again I’ll say that it’s best to keep the inside wall of the flue as close to plumb over the throat which is 8 to 9” back from the face and all the way up to the top of the chimney and if not possible, a gentle slope back is a must.In certain situations we had the entire section of wood wall left open right to roof and kept the chimney half into the room with flashing incorporated at the jambs,especially on cathedrals. We never set the throat back further to form a thick breasted wall that the straight back rumfords use, because it’s a sure recipe for eddys on a slanted rumford.

    In other words don’t expect the heat and smoke to be cast forward, but not past that thick front wall,”rounded breast or not” when it suddenly has to change direction and go backwards as it goes up,especially on those bad draft days. Some think that the thick breast wall is not an issue but it places the throat too far back to retrieve the upper smoke that is cascading along the very hot sloped wall ,of which already wants to come forward, and without the help of a sudden change in wind direction or other that causes a temporary draft pause.So where would one want the exhaust port in this sluggish time,..towards the back, or the front.

    Orton has done a nice job for a person with no hands on experience and having limited knowledge, and deserves better than some have written about him. His notable mistake of which would effect function is his mentioning that the fire back can rise 15”. Rumford was smart in noting that the slant should be as close to the fire as possible[I foud out the hard way in the early 70’s] therefore 8 to 10” and I think it was do to what he had seen around his home and about.

    I am a 3rd generation mason contractor in CT. and have developed a nice damper some 35 years back when I built a rumford in Westport,CT., that I’ve been meaning to patent,..but we all know how life can “slope” ones priorities otherwise.
    My son just started a web site that is in it’s beginning stage meanwhile If anyone needs some advice they can email casini25@aol.com. . http://www.casinimasonry.com/casinimasonry.html

    Also I have just placed a video of my 48” slanted rumford that works flawlessly and is used much used for days on end for over15 yearst It has the same damper. At the full open positiion it’s 3-1/4” by 48” but I can and do lower it to around 2″ when all is hot and I don’t want a large fire [one more than 4 logs. This is contrary to the statement of a slanted rumford having almost twice the size damper area that his true straight version has thereby resulting in excess loss of heat,and the prone to smoke statements and others. I am not the writting type but as of late in reading certain statements floating around out there with regards to what is true and what is not in the world of Rumfords I am compelled to tell my version of true not smoke and mirror tactics that bolster the wheel invention with that steel rim while we now have the rubber one…
    I am about to start heat testing it with a thermometer set at the throat and at other key spots and already easily achieved 600 degees at the back middle of the throat/damper,but more importantly I value the heat that radiates forward into the room, above that of a straight back and I think it obvious, as did the count. I’ll continue to put the vidios on youtube as I do them.

    http://www.youtube.com/results?search_query=fcasini25&search_type=&aq=f

    Frank Casini

    Count Rumford’s Foot note ;
    *
    Having been obliged to carry backward the fireplace in the manner here described, in order to accommodate it to a chimney whose walls in front were remarkably thin, I was surprised to find, upon lighting the fire, that it appeared to give out more heat into the room than any fireplace I had ever constructed. This effect was quite unexpected; but the cause of it was too obvious not to be immediately discovered. The flame rising from the fire broke against the part of the back which sloped forward over the fire, and this part of the back being soon very much heated, and in consequence of its being very hot, (and when the fire burned bright it was frequently quite red-hot,) it threw off into the room a great deal of radiant heat. It is not possible that this oblique surface (the slope of the back of the fireplace) could have been heated red-hot merely by the radiant heat projected by the burning fuel; for other parts of the fireplace nearer the fire, and better situated for receiving radiant heat, were never found to be so much heated; and hence it appears that the combined heat in the current of smoke and hot vapour which rises from an open fire may be, at least in part, stopped in its passage up the chimney, changed into radiant heat, and afterwards thrown into the room. This opens a new and very interesting field for experiment, and bids fair to lead to important improvements in the construction of fireplaces. I have of late been much engaged in these investigations, and am now actually employed daily in making a variety of experiments with grates and fireplaces, upon different constructions, in the room I inhabit in the Royal Hotel in Pall Mall; and Mr. Hopkins, of Greek Street, Soho, Ironmonger to his Majesty, and Mrs. Hempel, at her Pottery at Chelsea, are both at work in their different lines of business, under my direction, in the construction of fireplaces upon a principle entirely new, and which, I flatter myself, will be found to be not only elegant and convenient, but very economical. But as I mean soon to publish a particular account of these fireplaces, with drawings and ample directions for constructing them, I shall not enlarge further on the subject in this place. It may, however, not be amiss just to mention here, that these new invented fireplaces not being fixed to the walls of the chimney, but merely set down upon the hearth, may be used in any open chimney; and that chimneys altered or constructed on the principles here recommended are particularly well adapted for receiving them.

  3. Francis Casini March 16, 2010 at 8:11 pm #

    Try this link for the video http://www.youtube.com/user/fcasini25?feature=mhw4

  4. Francis Casini March 16, 2010 at 10:45 pm #

    This is Rumford’s preceeding paragraph to the footnote [I already posted] discussing the bedroom with the thin front walled fireplace that prompted his slanted back invention.

    [353]

    Of Chimney Fire-places.
    When the wall of the chimney in front, measured from the upper part of the breast of the chimney to the front of the mantle, is very thin, it may happen, and especially in chimneys designed for burning wood upon the hearth, or upon dogs, that the depth of the chimney, determining according to the directions here given, may be too small.

    Thus, for example, supposing the wall of the chimney in front, from the upper part of the breast of the chimney to the front of the mantle, to be only 4 inches (which is sometimes the case, particularly in rooms situated near the top of a house), in this case, if we take 4 inches for the width of the throat, this will give 8 inches only for the depth of the fireplace, which would be too little, even were coals to be burned instead of wood. – In this case I should increase the depth of the fireplace at the hearth to 12 or 13 inches, and should build the back perpendicular to the height of the top of the burning fuel (whether it be wood burned upon the hearth, or coals in a grate), and then, sloping the back by a gentle inclination forward, bring it to its proper place, that is to say, perpendicularly under the back part of the throat of the chimney. This slope (which will bring the back forward 4 or 5 inches, or just as much as the depth of the fireplace is increased), though it ought not to be too abrupt, yet it ought to be quite finished at the height of eight or ten inches above the fire, otherwise it may perhaps cause the chimney to smoke; but when it is very near the fire, the heat of the fire will enable the current of rising smoke to over-

    A A 3

    [354]

    Of Chimney Fire-places.
    come the obstacle which this slope will oppose to its ascent, which it could not do so easily were the slope situated at a greater distance from the burning fuel*.

    * Having been obliged to carry backward the fireplace in the manner here described, in order to accommodate it to a chimney whose walls in front were remarkably thin, I was surprised to find, upon lighting the fire, that it appeared to give out more heat into the room than any fireplace I had ever constructed. This effect was quite unexpected; but the cause of it was too obvious not to be immediately discovered. The flame rising from the fire broke against the part of the back which sloped forward over the fire, and this part of the back being soon very much heated, and in consequence of its being very hot, (and when the fire burned bright it was frequently quite red-hot,) it threw off into the room a great deal of radiant heat. It is not possible that this oblique surface (the slope of the back of the fireplace) could have been heated red-hot merely by the radiant heat projected by the burning fuel; for other parts of the fireplace nearer the fire, and better situated for receiving radiant heat, were never found to be so much heated; and hence it appears that the combined heat in the current of smoke and hot vapour which rises from an open fire may be, at least in part, stopped in its passage up the chimney, changed into radiant heat, and afterwards thrown into the room. This opens a new and very interesting field for experiment, and bids fair to lead to important improvements in the construction of fireplaces. I have of late been much engaged in these investigations, and am now actually employed daily in making a variety of experiments with grates and fireplaces, upon different constructions, in the room I inhabit in the Royal Hotel in Pall Mall; and Mr. Hopkins, of Greek Street, Soho, Ironmonger to his Majesty, and Mrs. Hempel, at her Pottery at Chelsea, are both at work in their different lines of business, under my direction, in the construction of fireplaces upon a principle entirely new, and which, I flatter myself, will be found to be not only elegant and convenient, but very economical. But as I mean soon to publish a particular account of these fireplaces, with drawings and ample directions for constructing them, I shall not enlarge further on the subject in this place. It may, however, not be amiss just to mention here, that these new invented fireplaces not being fixed to the walls of the chimney, but merely set down upon the hearth, may be used in any open chimney; and that chimneys altered or constructed on the principles here recommended are particularly well adapted for receiving them

  5. Francis Casini March 18, 2013 at 7:18 pm #

    As of recent I have been testing my Orton Style Slanted Rumford with my damper at just 1-1/2” which is a 1 to 30 ratio “throat to opening”. This now has about 150 hours of fires in all types of weather even heavy fog with no movement. I’ll soon show a up close video with throat opening verification. The normal ratios from what I read at Buckley Rumford and all over the internet, are best-ed at 1/20th for straight backed Rumfords which prowdly boast only 1/17 to 1/20. Meanwhile videos and info and pics can be seen at casini masonry at facebook. http://www.facebook.com/pages/Casini-Masonry/159609824086030?ref=hl

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