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Background: Test Description

We tested the six stoves side-by-side at the Alliance for Green Heat in a simulated “real-world” test lab located in Takoma Park, MD. The six stoves were anonymously purchased from several retailers in the United States in Maryland, New York, and New Jersey. The stoves were chosen based on interviews with scores of retailers about which were their best selling North American and European stoves. The stoves were first tested at Brookhaven National Laboratory, which will produce an academic report on their testing, which included emissions in grams per hour (PM 2.5) and the efficiency, based on CSA B415.

The stoves were tested in a screened-in porch that was open to outside air. The stoves were all installed with DuraVent brand PelletVent Pro venting systems, double walled piping with an inner wall of stainless steel and a galvalume outer wall that is sealed by metal-to-metal connection. In addition to venting pipe, the freestanding stoves were installed with a PelletVent Pro Tee for easy cleanout. The hole for the Testo 320 probe was drilled at 6 feet above the floor. (Eight feet, specified by ASTM, was not possible because the venting needed to exit the side of the structure below 8 feet on several stoves)

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Figure 2. Power setting distribution during 30-day testing
period (0=off, 1=low, 2=medium, 3=high) and most testing was done at the medium setting.

The six stoves were loaded with pellets, turned on and operated nearly 24 hours a day, 7 days a week, for 30 days. The 30-day period began at 2:30 on September 2, 2015 and ended at 2:30 on October 2, 2015. Testing of the six stoves began on September 5, 2015. Some stoves periodically burned only 20 – 22 hours if they ran out of pellets in the middle of the night, particularly at high burn rates. The stoves burned at high for 127 hours and 45 minutes, at medium for 262 hours and 33 minutes, at low for 281 hours and 50 minutes, and were off for 46 hours and 22 minutes (due to cleaning and more specific testing goals).

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Figure 3. After several hours of use, the filter in the Testo gets dirty and needs to be switched out with a new one.

All six stoves were tested in the same way to the maximum extent possible. Stoves were set to override room temperature settings in order to stay burning at a set heat output level throughout the experiment. Stoves were powered on and set at low, medium or high power setting, and operated for 1 hour at that setting before the start of testing. After burning for an hour to reach steady state, the stoves were tested for 15 minutes each using a Testo 320 Combustion Analyzer. The specific parameters were set on the Testo 320 (Flue gas analysis; 10% moisture wood), and it was zeroed in open air before each test. Zeroing of the Testo 320 ranges from a 30 second rinse to a 3-minute rinse and indicates on the screen when the instrument has finished zeroing. During each 15-minute test, the Testo 320 took readings each second, recorded on a computer using Testo EasyHeat software and averaged to obtain daily values.

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Figure 4. Comparing numbers from the Wohler 550 and Testo 320.

The Testo 320 was purchased specifically for this experiment, came with pre-calibrated sensors, and not used before the start of the 30-day burn period. Filters on the Testo 320 were visually inspected for soot build-up and changed frequently, and dates for filter changes were recorded. During filter changes, compressed air was used to clear the probe shaft. The condensate container was emptied every week before the start of testing but frequently had little to no condensate accumulation.

At the beginning of the 30 days of testing, we hired Biomass Controls, Connecticut, to simultaneously test with a Wohler 550 flue gas analyzer to verify readings on the Testo.

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