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by Paul Tiegs

Initial OMNI Report - graphs
Full OMNI Report


Since it has been very difficult to get a general understanding amongst regulators of the issues between using the grams-per-hour (the reporting unit used for woodstove emissions) and the grams-per kilogram of fuel burned reporting unit most appropriate for fireplaces, I will keep the discussion in g/hr.

The U.S. EPA's 7.5 grams per hour (g/hr) emission limit for woodstoves is actually a calculated weighted average of four different tested burn rates (measured at four different times during a full burn cycle). Those measured rates may range from 1 kilogram per hour (kg/hr) to the maximum rate a stove will burn.

In addition to the g/hr limit, the EPA also stipulates a single, maximum burn rate test limit of 18 g/hr (Federal Register Volume 53, Number 38, page 5860, February 26, 1988), which applies to woodstove tests that produce single-measure readings of more than 1.5 kg/hr.

Fireplaces do not have burn rate control mechanisms, as do woodstoves. It is impossible, therefore, to "choke down" a fireplace to reach the lowest burn rate achievable by a woodstove. Therefore, when establishing a "fireplace equivalent" of the EPA woodstove test, it is reasonable to apply the EPA burn rate test limit cap of 18 g/hr.

The second conversion that is required when establishing a "fireplace equivalent" relates to the test methods used for measuring woodstove emissions and fireplace emissions, respectively.

One of the primary differences between the approved woodstove test methodology and the approved fireplace test methodology is fuel loading. When fueling a woodstove test, the prescribed test-fuel load (cite authority for fuel quantity/quality) is placed on top of a hot, burning coal bed. When fueling a fireplace test, the prescribed test-fuel load is placed in a cold fireplace and ignited.

Another significant difference relates to the timing of sample-capturing. For example, fireplace test sampling is begun immediately upon lighting the test-fuel load from a cold start. Woodstove test sampling does not begin with a cold start, but only after a hot burning coal bed is under the test-fuel load to be measured.

These differences, if not corrected, produce patently incomparable results. Well-accepted research by Shelton Research Laboratories (Santa Fe, New Mexico) has demonstrated 33% of total fuel-load emissions is produced during the kindling phase of the combustion cycle. In order to derive data that is useful and comparable, therefore, a "fireplace equivalent" of the EPA woodstove certification test must include a factor to neutralize the differences in the state of combustion at which sampling is initiated. Since the Northern Sonoma County Air Pollution Control District's protocols (which the BAAQMD approves unconditionally) prescribe a single test with three serial fuel loadings only the first of which are started with kindling, the adjustment factor proposed by OMNI is 11% (i.e., 1/3 of the 33% emission factor which has been attributed to the kindling phase), or 1.11 times the EPA 18 g/hr. cap.

Finally, there must be an adjustment to compensate for the differences in the way exhaust air samples from the respective woodburning devices are captured and measured. EPA woodstove certification tests use EPA's Method 5H (Title 40 CFR, Part 60. [Appendix A]) which is fashioned after EPA's standard Method 5 for measuring particulate emissions from industrial sources. Fireplaces are sampled using a high-efficiency sampling system (ESS) favored by the Northern Sonoma County Air Pollution Control District and endorsed by the Bay Area Air Quality Management District. In addition to capturing all the emissions captured by EPA's Method 5H, the ESS captures the semi-volatiles produced by woodburning, in an absorbent resin trap (designated as XAD-2). The effect of requiring this much more effective sampling technology -- designed specifically for maximum efficiency with woodsmoke sampling -- is that the captured-emissions readings are higher than they would be if EPA's Method 5H were used.

Thus, after adopting the EPA burn rate test cap of 18 g/hr, a truly transparent "fireplace equivalent" to the EPA woodstove certification test must include adjustment factors to neutralize significant disparities in both kindling phase sampling methods and emissions-capture efficiencies.

OMNI Test Laboratories proposes the following formulation:

18 g/hr x 1.11 (kindling phase factor) x 1.385 (capture efficiency factor) = 27.7 g/hr Emissions Cap for Fireplaces as measured by the Northern Sonoma Fireplace Testing Protocols.

OMNI is one of four national laboratories licensed by the EPA to perform the EPA woodstove certification test and site of recent comparative analyses sponsored, in part, by the BAAQMD and the Northern Sonoma Air Pollution Control District.


Pictures of the fireplaces being built and tested

Buckley Rumford Fireplace Emissions Test Results
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Buckley Rumford Fireplaces
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