The Northern Sonoma fireplace standard fueling protocol rules require that the weight of the fuel be proportional to the inner hearth area. The rules also require that the fuel be placed horizontally within the firebox. These rules put the tall shallow Rumford fireplaces at a severe disadvantage.
By any meaningful measure the Rumford fireplace is a larger fireplace by about one third than the other three masonry fireplaces and one metal fireplace tested yet the fuel load permitted in the Rumford, based on hearth area, can only be a little more than two thirds of that permitted in the other fireplaces.
For a couple of hundred years the design guides, currently reflected in all the national building codes, determine the throat and flue cross-sectional areas based on the cross-sectional area of the fireplace opening. The cross-sectional area of the opening (or perhaps the firebox volume) - rather than hearth size - should be the basis of the fuel load.
The rules also restrict the placement of the fuel in the way most beneficial to a Rumford fireplace. The Rumford is a tall, shallow, vertical firebox. Firewood is most advantageously placed in the fireplace vertically. Even though the fuel can be placed horizontally, placing the logs vertically leaning against the straight and narrow fireback results in a cleaner, more efficient and structurally more stable fire.
We considered splitting the wood into smaller pieces (which is permitted by the rules) so that it would burn faster - about as fast, albeit for a shorter time, as the larger fuel loads in the smaller fireplaces - but in the end to give the rules a fair test, OMNI staff convinced us to use 4"x4"s wired together like the fuel loads in the other fireplaces.
We also decided to pay for another test with a fuel load appropriate to the Rumford.
We recalculated all the fuel loads based on firebox volume rather than hearth area. The fuel load for each fireplace was determined in Kilograms by multiplying the firebox volume in square feet times 3.5. This did not change the fuel loads for the two fireplaces that had fireboxes 24" tall. It increased the 27" tall fireplace only slightly but resulted in a 50% increase in the fuel load for the 36" tall Rumford fireplace.
We also split some of the dimensional 4"x4"s and, of course, placed the fuel on end, tipi style - the way it burns best in a Rumford. George Erdman at Northern Sonoma was quoted as saying, "I don't want any teepee fires or other fueling tricks." Here are a couple of pictures. Which set is more "tricky"?
NS Rules: Fuel (kgs.) = hearth area (sq.ft.) X 7 - length between 1/2 and 5/6 average firebox width
4"x4" dimentional lumber wired together in attempt to be as consistent as possible fell out of both conventional and Rumford fireplaces.
Proposed Rules: Fuel (kgs.) = firebox volume (sq.ft.) X 3.5 - length between 1/2 and 5/6 average firebox width
4"x4" dimensional lumber (some split) standing vertically was stable and needed no wire and minimal tending.
Letter to George Erdman and response from Barbara Lee
Emission and efficiency results to be announced
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