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Fuel Crib Testing
Feb. 2005

Summary of Results
Fuel Crib Description
Fuel Crib Calculation
Comments and Conclusions

See also: Alaska Research Heater


As part of the ASTM standards process, the masonry heater subcommittee is proposing a standardized fueling protocol that can be used
for emissions, efficiency and safety testing.

A first step is to qualitatively compare a firing using the current draft fuel crib with a firing using a typical fuel load, for several different
sizes of heater.

The first tests were done by Lopez Labs on a 22" Heatkit heater located near the Lopez facility in Shawville, Quebec.

The fuel was documented, and a photographic record was made of burns with a draft ASTM crib and a normal load.

The normal load in this case was 8 pieces of sugar maple, at 14.5% moisture, with a total weight of 65 lbs.

The test pieces for the draft ASTM fuel crib were rough sawn 4x4's which, unfortunately, got over dried to 8%.

Summary of Results:

Normal Run, 65 lb Sugar Maple
ASTM Draft Fuel Crib, 4 x 4 Spruce



Fuel Crib Description:

The fuel pieces are numbered consecutively 1 - 8 as follows:

First row: - left to right
Second row: - back to front
Third row: - left to right
Fourth row: back to front

The weights were as follows:

1: ___8 lbs
2: ___8 lbs
3: ___6.5 lbs
4: ___10 lbs
5: ___7 lbs
6: ___8.5 lbs
7: ___8 lbs
8: ___9 lbs

Kindling was 1 lb. of poplar, plus 3 double pages of newsprint.

See fuel calculation below.

Total weight:

Kindling: 4.7 lb

Main load: 32.3 lb

Description for ASTM draft test crib (right):

First tier of newspaper crib (.75" x 1.5" pieces) was calculated at 8.4" (allowable minimum). Because this heater has sloped inserts in the sides of the firebox floor, the pieces did not quite fit on a diagonal, as specified.

Calculated second tier of .75" x 1.5" newspaper crib requires 22" pieces. In order to make them fit, one piece was cut as shown, above on the right.

The specified three pieces of crumpled double page newsprint did not fit in the space provided. One piece was put in, and the other pieces were put off to the side as shown. Once the crib was stacked, some of them were shoved underneath, to provide an ignition path.

Second kindling tier of 22' pieces of 1.5" x 1.5" (2" x 2" actual). One piece was cut as shown.

First crib tier of 1.5" x 3.5" (2" x 4" actual), shown with .75" spacers nailed in place.

The spacers on the bottom are an error.

The specification calls for left-to-right orientation. However, this was judged unstable, and front-to-back orientation was used instead.

Two tiers of 3.5" x 3.5" (4" x 4" actual), with .75" spacers.

Each tier is 3 pieces. The specification called for a third tier of 2 pieces, but these would not fit and were not placed.

If the fuel pieces followed the specification exactly, the top of the crib would be 2.75" lower, and a top tier would just fit.

The fuel piece actual length was 16.75". The calculated length was 15.38"

The main deviation from the specification was the fuel moisture, which is supposed to be around 20%. The actual moisture was 8% for the main pieces, and 20% for the kindling tier. The fuel was purchased green from a local sawyer, and overdried by accident.


Moisture meter with calibration device.
All wood was taken from the same batch, which has been under cover for
4 years. In order to obtain a moisture value, several sample pieces were re-split and
the readings taken from a freshly split face.

Weight scale calibration. 2 kg bag of flour reads 4.4 lbs.

Typical piece of fuel. Weight: 8.75 lbs.


Heater doors were replaced with a piece of ceramic glass to allow photographing an unobstructed view.
In the photo sequence for the standard load, some soot is visible near the top of the glass in the 10 -30 minute range,
at which point it burns off. This could be avoided by adding a small gap between the top of the glass and the door
frame to create an air wash.

Photographs were taken with a Nikon Coolpix 995 digital camera set on a tripod, with a fixed exposure
of 1/60 sec at f-4.6, with an ASA equivalent of 200.

The camera was operated with an M-105 Palm Pilot running the freeware program "Palmshot".
It turns the Palm Pilot into a time-lapse controller for the camera through a serial cable connection.


Fuel Crib Calculation:

Note: the above is a screenshot of a fuel crib calculator developed by OMNI-Test and presented at the Feb. 26/05 ASTM masonry heater task group meeting in Atlanta.
It supercedes the manual calculation used for the first fuel crib test.

Comments and Conclusions:

This was the first attempt to run the draft protocol.

The fuel crib burned faster than the normal load. This can be partly attributed to the drier fuel. Therefore, a
repeat test is required in order to eliminate this variable.

Using 4x4 rather than the specified 3.5 x 3.5 fuel did not allow the full fuel crib to be stacked.

Some kindling stacking issues were highlighted, and should be addressed by the subcommittee.

Preliminary visual testing such as this should be done on several other heater models.


See also: Alaska Research Heater


This page was updated on March 4, 2005

This page was created on February 5, 2005