Buckley Rumford Fireplaces
Draft Masonry Fireplace Method
Notes & Issues


Preliminary OMNI Test Result Evaluation, 4/12/07

Need to stick to consistent units.

Weight/volume of crib:

Crib by opening area - Fuel-load cribs shall be determined by the fireplace opening area. The weight of each crib in pounds shall be three times the opening area of the fireplace in square feet (calibrated to E-36), less one tenth of the weight of fuel over 12 pounds to adjust for the advantage of larger fuel loads. The fuel length shall be half of the firebox dimension in the direction of fuel placement with fuel lengths no less than 16" nor greater than 24" except for one piece that may be any length shorter than all the rest of the pieces as needed to achieve the required crib weight. Three separate fuel-load cribs shall be prepared. The first fuel crib shall be made up of nominal 1.5- x 3.5-inch (38- x 89-mm) fuel pieces. The second and third fuel crib loads are made entirely of 3.5- x 3.5-inch (89- x 89-mm) fuel pieces.

Crib by volume -

Crib by algorithm - Too complicated. If "adjusted" volume of std fireplace is 5.09 cu.ft (actual volume is 7.08 cu.ft.) and loading factor is 15% then volume of fuel is 0.7635 cu.ft. - or 1,320 cu.in - which weighs about 30 pounds.
3.5"x3.5"x107.75"=1,320 - six 18" 4x4s
I piled up 30# of dry Doug Fir and it's volume was 1,577 cu.in. yet weight of fuel in run numbers 7-12 are around 15 to 19 lbs. Is it somthing about the "square rule" that goes disjunctively from nine 4x4s to four and won't allow six?

Scaling by Opening Area, volume and Algorithm

Heatilator E-36

    E-36 firebox: 30" wide, 16" to smoke shelf (opening is 18 tall), 14" deep, 20" wide fireback
    Opening area 30"x18"= 540 sq.in. or 3.75 sq.ft.
    Firebox volume: hearth area (30+20)/2=25x14=350 sq.in.x16"=5600cu.in/1728= 3.24 cu.ft.

    Crib by opening area: 3.75 x 3 = 11.25 lb.
    Crib by volume:
    Crib by algorithm: 0.37 cu.ft. (10.6 to 11.5 lbs.)

36" standard firebox:
    36" wide, 24 tall, 17" deep, 24" wide fireback
    Opening area: (36"x24" = 864 sq.in. or 6 sq.ft.
    Firebox volume: hearth area (36+24)/2=30x17 =510 sq.in. x 24" = 12,240 cu.in / 1728 = 7.08 cu.ft.

    Crib by opening area: 17.6 lbs (6 x 3 = 18 lb. - 1/10 (18 - 12 = 4) = 17.6 lbs.)
    Crib by volume:
    Crib by algorithm: 1.3 cu.ft. (38.4 to 49.4 lbs.) at 25% loading factor or
    Crib by algorithm: 0.5 cu.ft. (15.1 to 18.7 lbs.) at 15% loading factor

    Note: "adjusted" volume = 5.09 cu.ft. at 25% a loading factor each crib has a volume of 1.2725 cu.ft. or, using a 15% loading factor, 0.7635 cu.ft. - from Bruce's notes during testing.
    1.3 cu.ft. at 25% loading (with weights from 38.4 to 49.4 lbs.) and 0.5 cu.ft. (with weights from 15.1 to 18.7 lbs.) according to Tiegs, 7/07 but arithmetic doesn't work out.

36" Rumford "Rumford Fireplace was not tested. Fuel load volume was calculated at 0.44 cubic feet with .25 loading factor." - Tiegs, 7/07
    36" Rumford firebox: 36" wide, 36 tall, 14" deep, 13.5" wide fireback
    Opening area: (36"x36" = 1,296 sq.in. or 9 sq.ft.
    Firebox volume: hearth area (36+13.5)2=24.75x14 =346.5 sq.in. x 36" = 12,474 cu.in / 1728 = 7.22 cu.ft.

    Crib by opening area: 25.5 lbs (9 x 3 = 27 - 1/10 (27 - 12- = 15) = 25.5 lb.)
    Crib by volume:
    Crib by algorithm: 0.44 cu.ft. (about 15 lbs) at 25% loading factor

    Note: Why 25% loading factor? Note less fuel than smaller 36" std fireplace.

Advantage of large fuel loads
Fireplaces are single burn-rate appliances - can't build fires too small or too large. Optimum fires are good. If it turns out that the larger the fireplace opening the larger the fire and the better the emissions results, we could figure out how much advantage that is and adjust for it by reducing the fuel load for larger fireplaces by using a formula sort of like this: "The weight of each crib in pounds shall be three times the opening area of the fireplace in square feet, less one tenth of the weight of fuel over 12 pounds to adjust for the advantage of larger fuel loads." Could be, after testing, that the adjustment should be one eighth or one twelfth. If you allow negatives, the formula would allow larger fuel loads for fireplaces with less than 12 pound cribs.

Load more often to maintain more even fire.
If we reloaded at 35% or even 50% O2 recovery there would still be some flame and unburned fuel (typically the time anyone would reload a fireplace). Tiegs cites two objections: 1) real world is in conflict with reproducibility and 2) the fuel will keep getting larger and more unmanageable. Firstly, reloading at 50% recovery is even more precise and reproducible than reloading at 70% since the margin of error of 10% in O2 readings is less critical when the fire is stable than it is at a time when the O2 levels are near ambient and the fire may be nearly out, and secondly the fuel load won't keep getting larger and the unburned fuel would not just accumulate because the burn rate would increase slightly and the fire would stabilize. Yes it's a way to get a larger cleaner fire but it avoids both the overfire objections of loading too much fuel at once and the nearly out problem of reloading too late.

Fireplaces are different than stoves and masonry heaters. That's why we have recognition of the need for a separate fueling protocol. If not why are stoves and masonry heaters allowed larger fuel loads because they are different? If real world isn't an objective then let's keep the standard fuel loading the same as it is in heaters and stoves at 25% or so - or require stoves and heaters to use 15%. The whole issue is whether a batch loading protocol suits an open fireplace or not.

Other Issues


Issue is more method of heat transfer
Radiant Efficiency
ANSI standard
Stove and masonry heater efficiency

Difference in perspective or nefarious objectives, cooked science and deception?

All the studies done by people more familiar with and who stand to benefit from closed combustion chamber appliances
The AP42 Study
Graph in SCAPCB

Standard 36" Masonry Fireplace
Buckley Rumford Fireplaces
Copyright 1996 - 2007 Jim Buckley
All rights reserved.