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Austrian Eco Firebox Testing

This page was created on March 1. 2014
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June 18, 2014 update by Boris Kukolj


The heater in the lab has a replaceable firebox liner. The standard liner of  firebricks on edge was replaced with this one.
After the second course, the horizontal joints are shimmed open to create 5mm air slots.
See Austrian specifications for firebox.


For this testing, the grate air was shut off.
Underfire air could be used to burn up the coals at the end, to allow the chimney damper to be closed earlier.
In the Austrian system, the stove is airtight. Chimney shut off dampers are not permitted. 
The air is shut off when the load is reduced to a charcoal bed.




Cross section of supply channels is 26.25 sq. in.
Cross section of horizontal firebox air slots 27 sq. in.


Air enters air frame from below and is fed out the sides into the horizontal firebox 5mm air slots.
There are also 3 mm air slots cut into the 4 inside corner edges of the air frame, aimed 45 degrees towards the firebox.


View from firebox, showing air horizontal and vertical air slot in air frame, aimed 45 degrees at the fire.
Air frame is 3"x4" tubing. Total cross section of both legs is  20.6 sq. in.


View of top horizontal slot on air frame, aimed down at the fire at 45 degrees.


Click for video

Test Results



Runs GH-01 - GH-18 were by Homestead Heat, see below


Update from Lopez Labs member Boris Kukolj, June 18, 2014:


Gas graph 1,  Condar spreadsheet 1
Gas graph 2,  Condar spreadsheet 2









Homestead Heat Testing:


Double bell heater with eco-firebox, Homestead Heat
See testing summary, above

Time lapse of run GH-18


Heat-Kit Testing:

March 20/14 - HK-M34 click on test numbers for full data

Red oak cordwood, big pieces
Side ignition.  Newspaper 3/4 up the kindling pile.
58.3 lbs including 5.0 lbs kindling
19.7% moisture.

0.58 g/kg PM (Condar)
20.071 g/kg CO
75.09% overall efficiency

March 19/14 - HK-M33

Red oak cordwood, big pieces
Side ignition.  Newspaper 3/4 up the kindling pile.
60.7 lbs including 5.5 lbs kindling
16.4% moisture.

0.41 g/kg PM (Condar)
13.97 g/kg CO
75.35% overall efficiency

March 18/14 - HK-M32

Sugar maple cordwood. 
Side ignition.  Newspaper 3/4 up the kindling pile.
59.5 lbs including 5.0 lbs kindling
19.0% moisture.

0.47 g/kg PM (Condar)
13.92 g/kg CO
75.35% overall efficiency

March 17/14 - HK-M31

Sugar maple cordwood. 
Side ignition.  Newspaper 3/4 up the kindling pile.
68.2 lbs including 5.5 lbs kindling
18.3% moisture.

0.55 g/kg PM (Condar)
14.34 g/kg CO
74.52% overall efficiency

March 16/14 - HK-M30

White birch cordwood. 
Side ignition.  Newspaper 3/4 up the kindling pile.
50.6 lbs including 5.00 lbs kindling
15.5% moisture.
2 dry pieces on top caused too fast a start.

1.29 g/kg PM (Condar)
26.46 g/kg CO
71.36% overall efficiency

March 13/14 - HK-M29

White birch cordwood. Small wood, cold fuel
Side ignition.  Newspaper 3/4 up the kindling pile.
42.4 lbs including 3.75 lbs kindling
15.5% moisture.

0.96 g/kg PM (Condar) - estimated due to lack of 1 clean filter weight
16.04 g/kg CO
72.32% overall efficiency

March 10/14 - HK-M28

Data loss due to power failure. Photographic record only.

Red oak cordwood. Large wood. Average piece weight 5.4 lbs
Side ignition.  Newspaper 3/4 up the kindling pile.
71.2 lbs including 6.2 lbs kindling
23% moisture (est)

March 9/14 - HK-M27

Red oak cordwood. Small wood, higher moisture than HK-M26
Side ignition.  Newspaper 3/4 up the kindling pile.
67.8 lbs including 6.0 lbs kindling
22.9% moisture.

0.53 g/kg PM (Condar)
13.61 g/kg CO
74.75% overall efficiency

March 8/14 - HK-M26

Red oak cordwood. Large wood.
Side ignition.  Newspaper 3/4 up the kindling pile.
60.1 lbs including 5.2 lbs kindling
18.7% moisture

0.46 g/kg PM (Condar)
16.76 g/kg CO
74.35% overall efficiency

March 7/14 - HK-M25

White birch cordwood. Large wood, mix of wet and dry (see fueling details in Condar spreadsheet)
Side ignition.  Newspaper 3/4 up the kindling pile.
61.7 lbs including 5.2 lbs kindling
22.4% moisture
Cleanest burn to date on this heater.

0.46 g/kg PM (Condar)
13.39 g/kg CO
73.60% overall efficiency

March 6/14 - HK-M24

White birch cordwood.
4 lbs kindling on left side. Newspaper 2/3 up the kindling pile.
49.6 lbs including 4.00 lbs kindling
20 % moisure (estimated)
Very staged start.

0.89 g/kg PM (Condar)
15.33 g/kg CO
73.10% overall efficiency

March 5/14 - HK-M23

White birch crib. Crib turned 90 degrees from HK-M22
3.75 kindling on left side, as opposed to kindling on both sides, on HK-M22
37.1 lbs including 3.75 lbs kindling
15.1% moisure

Compare with HK-M22, below. It used the same crib and kindling, except the
crib was turned 90 degrees and the side kindling was on one side instead of both sides.

This test series has established the excellent repeatability of cribs for masonry heater testing, and
this is a good demonstration of how fuel and ignition geometry in the firebox affects emissions.
In particular, there is a dramatic effect on particulate (PM) emissions, but only a very small effect
on CO emissions in this example.

Compare with HK-M22, below

0.93 g/kg PM (Condar)
20.57 g/kg CO
72.63% overall efficiency

March 4/14 - HK-M22

White birch crib. Ignition from both sides.
40.6 lbs including 3.75 lbs kindling
15.7% moisure

Compare with HK-M22, above

2.68 g/kg PM (Condar)
23.81 g/kg CO
71.70% overall efficiency

March 3/14 - HK-M21

White birch cordwood. Large wood, top ignition
57.2 lbs including 4.0 lbs kindling
15.5% moisure
Stack temperature corrected for height.

Top ignition

1.35 g/kg PM (Condar)
17.31 g/kg CO
73.26% overall efficiency

March 2/14 - HK-M20

White birch cordwood
46.0 lbs including 4.0 lbs kindling
15.2% moisure
Stack temperature corrected for height.

Too much newspaper, too fast a start

1.46 g/kg PM (Condar)
16.01 g/kg CO
73.26% overall efficiency



This page was updated on July 29, 2014
This page was created on March 1. 2014